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In 2024, which is now slowly drawing to a close, we have spent a lot of time adjusting the quality of our brewing water so that it is reproducible. The background to this is that Stadtwerke Clausthal installed two new waterworks in 2023 and is now liming the water to a hardness of 5-6 °dH. This process obviously required a certain learning phase, but for a good 3 months we have been measuring largely constant values of 5-6 °dH in our tap water. We have installed two reverse osmosis systems that supply us with demineralized water at an acceptable flow rate of 3 liters per minute, and we can now mix our brewing water as required.
With the water now very soft again, we have made a few attempts to brew Pilsner beers, as a Pilsner requires very soft water in order to emphasize the hop aroma. As a result, we currently have a relatively large number of rather simply brewed pilsner beers for upcoming events. On the other hand, sales of Pilsner beers are declining at industrial breweries and we are finding that the keg of Pilsner is always the last to be emptied at events, if at all.
As we are slowly having to start designing and brewing the beers for Clausthal University of Technology's 250th anniversary celebrations, we will once again be concentrating more on dark beers with a strong character, black beers, subtly fruity and aromatic Helles and Pale Lagers, low-alcohol Bock beers and, in particular, Pale Ale beers. With the latter, the flavors can be varied almost at will, and with the latest hop products and the odd "trick", the alcohol content of our pale ale beers remains low.
With a few exceptions, we always brew using the isothermal high-temperature mashing process, with which we achieve alcohol contents of between 2 and 2.5 % vol. at an original wort of 11 °P, depending on the mashing process. From time to time, we will also brew non-alcoholic beers with maltose-negative yeasts, but they will remain the exception due to the high price of these yeasts and the very high effort involved, including pasteurization. For the 250th anniversary celebration, we will brew a non-alcoholic pale ale with a maximum of 0.5% alcohol by volume and a pale ale with only 0.5% alcohol by volume. We will also be producing small quantities of gluten-free beers, one of which will be a fruit-flavored cold-hopped pale ale made exclusively from quinoa.
The Journal of the American Society of Brewing Chemists has accepted for publication our latest manuscript entitled
"Mashing isothermally at high temperature compared to infusion mashing for the production of full-bodied, alcohol-reduced beer"
. In this work, we brewed Pilsner beers using three different mashing methods and carried out each experiment three times to ensure statistical reliability.
We mashed once using the standard high-short method, once using a simplified high-short method (heating to 72 °C immediately after mashing), and once using the isothermal high-temperature mashing method at 72 °C, always mashing for one hour. We obtained almost identical original wort in all trials. The finished beers were all sensory evaluated at the Research Center for Brewing and Food Quality at the Technical University of Munich (aka "tasting"), and the conclusion was:
"The beers were rated on a scale of 1 to 5 (the tasters are only allowed to give whole marks) by the certified tasters according to the hypothetical ideal type of this beer type in all aspects, with 1 representing the lowest ranking and 5 representing the ideal value. It should be noted that a value of 4 still means that no off-flavors could be detected and it would still be possible for the beer to be bestowed an DLG award in Gold. The results show that all three beers scored well above 4.0 in all five attributes and the descriptive results showed very similar results (data not shown). Interestingly none of the certified tasters missed the alcohol content in the low alcohol beers done with isothermal mashing procedure."
The trials for this publication were carried out in summer and fall 2023 based on numerous preliminary trials from fall 2022, in which the malt pipe technique showed a lack of reproducibility. After an extensive evaluation, the manuscript was submitted for review at the end of June 2024. If you look a little at the older literature, our result is not really surprising, because the aroma build-up by conventional yeasts is completed after reaching approx. 2 % vol. alcohol, after which only alcohol is formed. This means that we can now answer the frequently asked question "Do your half beers even taste like real beers?" with a verifiable YES.
On 15.7.2024, we were looking for yeasts at two locations in the Harz Mountains with the support of the state forestry department, and on 3.8.2024 reports appeared in various local newspapers. We received many calls pointing out very old oak trees. You can estimate the age of trees very roughly based on the trunk diameter or circumference, and there are websites on the Internet for this purpose. 600-year-old oaks, which are often found in Sweden, have a trunk diameter of 2.5 meters, 200-year-old oaks about 1 meter, although these values should only be taken as a guide.
The oaks we sampled were a good 200 years old, and we found different yeasts at two different locations. We don't want to anticipate the results of our colleagues at the Technical University of Munich, but we found (at least) two different beer yeasts as well as wine yeasts - but unfortunately not Saccharomyces Eubayanus. As we still lack a fundamental understanding of which yeasts occur on which trees under which climatic conditions, we will be looking for yeasts in other places again in September with our lecturer and the state forests. And there is a very old ash tree just around the corner from the institute that could also be interesting.
At the TU Munich in Freising-Weihenstephan, Priv.-Doz. Dr. Mathias Hutzler has been supervising the "Yeast Hunt" project at the Research Center for Brewing and Food Quality there for many years (search terms: TU München; Hefejagd; Mathias Hutzler).
The colleagues are driven by scientific curiosity because of the estimated 1 million naturally occurring yeasts, perhaps 100 are used for the production of beer, and even fewer on an industrial scale. In the successfully completed dissertation by Dr. Yvonne Methner, numerous aroma yeasts were examined at the Technical University of Munich with regard to their potential for the production of beer. Today, most bottom-fermented beers in Germany are produced with the so-called W34/70. This is a yeast that gives the beers a harmonious character and, thanks to its very good sedimentation behavior, makes the large-scale brewing process through to final filtration very efficient. We also have excellent experience with this yeast and with Diamond from Lallemand Brewing, especially with the filtration of our beers. So why should we even bother looking for new yeasts when the subject of beer seems to have been researched beyond the brewing sciences, and why are there actually degree courses or lectures on the subject of beer if there is nothing left to research? This is how the author of these lines began a conversation with a journalist in August 2023, who was very interested afterwards. For details on yeasts, please refer to the work of Mathias Hutzler; here we will only summarize a few thoughts on the subject.
In the USA, the course is currently being set strongly in the direction of low-alcohol, low-alcohol and alcohol-free beers, and the brewery "Athletic Brewing" has made a clear statement on this in a recent press release. All trends in the USA will reach Germany sooner or later. At Clausthal University of Technology, we have observed a high level of interest in our beers with only approx. 2.5% alcohol by volume at the events we supply. With maltotriose-negative yeasts, we are now even achieving alcohol levels of just 1.7% vol. at the typical original gravity of around 11 °P. We ourselves only know of two commercial maltotriose-negative yeasts for the production of beer; there are certainly more in the yeast banks. Some yeasts do not even fully utilize maltose and glucose, although they generally do, and with such yeasts the alcohol content of beers can be further reduced.
There are also numerous so-called maltose-negative yeasts that are suitable for the production of non-alcoholic beers with less than 0.5% alcohol by volume, such as Saccharomycodes Ludwigii, Cyberlindnera Misumaiensis or Cyberlindnera Saturnus, which produces a strong aroma of pears. If Pichia Kluyveri is fermented in a controlled manner in the presence of oxygen, it metabolizes the glucose, forming aromatic substances and carbon dioxide, but without producing alcohol. With these yeasts, which are still far from being fully developed, less or no alcohol is produced from the outset, which means that it does not have to be removed with a high energy input. Our isothermal high-temperature mashing process in turn reduces the formation of fermentable sugars with the accumulation of unfermentable sugars, making a combination with such yeasts a good idea.
Another aspect is that the W34/70 may one day suffer the fate of penicillium camemberti. This fungus is used in the production of Camembert, and there are those who fear that this noble mold, which gives Camembert its typical aroma, could become extinct in as little as 15 years. Whether this will happen is still unclear, but the cheese industry is already looking for alternatives, which will, however, be accompanied by a different taste. It is therefore also of fundamental interest to look for new yeasts in nature that could be suitable for the production of beer.
There is also another question that needs to be clarified. Bottom-fermenting yeasts such as W34/70 evolved from Saccharomyces Eubayanus and Saccaromyces Cerevisiae at some point during the course of evolution. Our lecturer, Dr. Martin Zarnkow, deals with this topic in his lectures with us. So far, Saccharomyces Eubayanus has been found in several places around the world, but not yet in Germany. Like molds, yeasts are ubiquitous and can be found in the bark of numerous trees such as oak, ash, elm, hornbeam and others. For a summary of the life cycle of yeasts, please refer to the habilitation thesis by Dr. Mathias Hutzler, which can be obtained directly from him.
On the one hand, the Harz has not been sampled so far, on the other hand, there are very old oaks in the Harz, some of which are over 400 years old. Together with Carsten Pfeil from the Zellerfeld Brewing Academy and two employees from the Lower Saxony State Forestry Department, we therefore set out on July 15, 2024 in search of yeasts using a sampling kit put together by our colleagues from the Technical University of Munich. The employees of the State Forestry Department, whom we would like to thank very much at this point, took us to areas around Goslar that are not actually accessible to the public, where we were able to sample trees. We were able to take samples of the bark of sessile oaks, hornbeams, ash trees and a sycamore maple, in some cases down to the cambium.
From the outside to the inside, a tree is made up as follows: Bark, bast, cambium, sapwood, heartwood and possibly pith. A tree grows as the cambium expands outwards and inwards. The bast transports the nutrient solution from photosynthesis in the crown of the tree to the roots, the sapwood transports water and minerals upwards into the crown. Yeasts are therefore preferably found in bark and bast, because the sugar-containing solutions are transported in the bast and the bast transforms into the bark on the outside. Yeasts are trapped in the bark by this process. This also explains why bark beetles and spruce bark beetles cause devastating damage to the spruce trees in the Harz Mountains. The beetles damage the cambium and bast, the roots are no longer nourished, and as a result the trees dry out due to the disrupted flow of nutrients to the roots and of water and minerals to the crown.
The oaks we sampled were 200 - 210 years old. We also took soil samples from the two different locations we sampled. All samples were taken sterile and packaged, immediately cooled and couriered to Mathias Hutzler's laboratory. We are curious to see whether we found any yeasts during this first yeast search in the Harz and which ones. As there are still many older oaks in the Harz Mountains, including very old ash trees, we may continue to hunt for yeasts in the Harz Mountains together with our colleagues from the Technical University of Munich, depending on the results. We are very pleased to be able to support the TU Munich's yeast hunting project.
Anyone who has ever visited a pub in the USA will have noticed a large selection of Pale Ale beers. And of course a Pale Ale, an Imperial Pale Ale, an India Pale Ale or a NEIPA is a "beer" there. Outside of Germany, raw fruit is also used for the preparation of beers, i.e. various unmalted starch sources. This can be barley or wheat, but rice, corn and quinoa are also used in certain proportions (up to approx. 40%). As a pale ale is dominated by the fruity, aromatic hop character and, depending on the type, also by a high bitterness, it is only possible for very experienced people to notice the use of raw materials other than barley malt in terms of taste.
In Germany, beers are brewed according to the so-called Purity Law. In its original version, this was an ordinance from April 23, 1516, which reduced the ingredients for the production of beer to water, barley and hops. Yeast was not yet known at that time, and an understanding of it was only developed with the light microscopic examination of this "stuff" by Louis Pasteur in the 19th century. This regulation, which was certainly influenced by various interests, was also the result of the so-called Little Ice Age. Wheat is quite demanding in terms of soil quality, and during this climatic phase, soil quality was limited, which led to shortages in the supply of wheat for bread. As barley, and even more so rye, is much more robust than wheat in terms of soil quality, the princes decided that barley had to be used for the production of beer. This regulation, known today as the Purity Law, makes no statement about the nature of the barley, i.e. not about malt, nor when and in what form hops can or must be added to the beer. Yeast was not known, but it was well known that without the "stuff" no beer would be produced.
If one interprets the text from 1516 as well as the common label "Brewed according to the German Purity Law of 1516" semantically strictly, a beer in Germany could only be brewed from barley, hops and water, and fermentation would even have to be carried out by yeasts from the air. On the other hand, this regulation was not referred to as the Purity Law in 1516, but it has been further developed over time, and in Germany, the so-called "Provisional Beer Law" of July 29, 1993 regulates exactly how beer is to be produced in Germany. In other words, any alcoholic beverage made from water, malt, hops and yeast that is to be labeled and marketed as beer must be produced in accordance with the requirements of this law, which ultimately represents the German Purity Law. This law is discussed in detail in our lectures, so we recommend that you research this law on the Internet - or attend the lecture in the summer semester. Section 9 is important with regard to the production of pale ale beers. Paragraph 5 sentence 1 states: "Hop powder and otherwise crushed hops as well as hop extracts must be obtained exclusively from hops." Paragraph 5 also states: "The hop extracts may only be added to the beer wort before the wort boiling process begins or during it."
A Pilsner beer made from barley malt is therefore a beer if both the bitter hops and the aroma hops were added during the wort boiling process or at least shortly before it ends. According to this law, there is freedom to use hop cones, hop pellets and hop extract in any combination during boiling if they have not been isomerized beforehand. "Boiling" is clearly defined thermodynamically and describes the first-order phase transition from liquid water to water vapor using water as an example. The boiling point, i.e. the temperature at which water boils, depends on the pressure, which decreases with increasing altitude. At the same time, the boiling point also decreases with increasing altitude. The Clausius-Clapeyron equation, which is discussed in the lecture "Physical Chemistry 1", describes this in more detail.
What happens if the aroma hops are first added to the whirlpool at approx. 95 °C to enhance the aroma of a Pilsner beer? Although water still evaporates and the molecules still change from a liquid to a gaseous state, the boiling point is no longer reached and boiling no longer takes place in the whirlpool. Beer produced in this way would therefore no longer be beer within the meaning of the law. When this law was drafted, the intention was also to ensure that a beer is a hygienically safe drink at all times. Various microorganisms, including foreign yeasts, can be found on hops, and adding them during boiling guarantees that these germs and mold spores are killed. Although cold hopping with hop cones or hop pellets, which has long been known internationally, was not unknown in Germany in 1993, it was rarely if ever practised and therefore played no role in the drafting of the law.
And hop extracts? Nowadays, bitter and aroma hop extracts are produced with supercritical carbon dioxide. The so-called critical point of carbon dioxide is around 31 °C and around 74 bar; for a more detailed description, please refer to the textbooks on physical chemistry or relevant tables. Above this temperature and pressure, carbon dioxide is neither a liquid nor a gas; it has transformed into a fluid that is used as a versatile extraction agent in food processing technology, including in the production of aroma hop extracts. Supercritical carbon dioxide can be considered one of the purest solvents in food processing technology, as it contains no impurities, and foods treated in this way comply with food law.
And why is such an extract only permitted for addition during cooking? The answer lies in the fact that chemical solvents were also used to extract hops in the past, even though many things have changed and improved in the 30 years since this law came into existence. It is basic knowledge in chemistry that even absolute solvents are never free of impurities, only solvents in HPLC quality achieve the highest possible purity, but this purity must also be paid for. If you then consider that halogenated solvents were also used to extract hops in the past, the legal text is very easy to understand: Boiling boils out any residual solvents, and no undesirable residues of these remain in the wort.
Although hop extracts are nowadays produced using supercritical carbon dioxide, you can also still find ethanol extracts, which, like the first mentioned, however, comply with food law. If any kind of dry hopping is practiced for the production of a Pale Ale, and strictly speaking this also applies to the whirlpool hopping of a Pilsner beer, such a beer, even if it was produced like a beer, looks like a beer, smells like a beer and tastes like a beer, actually contradicts the provisional Beer Act of 1993 and may not be marketed (in Germany) under the name "beer".
The following quiz question could be formulated: "What looks like a beer, smells like a beer, tastes like a beer and was produced like a beer, but is not a beer?" If such a beverage is not beer by law, it must actually be labeled as an "alcoholic beverage", an "alcoholic beverage in the style of a beer" or a "mixed beer beverage" in Germany, even if the obligatory list of ingredients does not allow any other conclusion than that it is a beer. Or you can apply to the competent authority for approval as a "special beer", but this incurs costs as the competent authority has to examine each application individually. This can quickly add up to a thousand euros or more to the bill. And it may well be that this designation can then only be used for a single recipe.
From this perspective, the question posed at the beginning is not so easy to answer, especially as the provisional Beer Act of 1993 appears to be set in stone for eternity. On the other hand, a cold-hopped Pale Ale is very close to the 1516 version of the so-called Purity Law, which makes no statement as to whether the hops may be processed and at what point in time they must be added to the beer. In this ambiguous situation, we therefore stick to the designation of the German Brewers' Association, where the types India Pale Ale and general Pale Ale, which are generally all cold-hopped in one way or another, are referred to as "top-fermented specialty beers". (Search words (14.07.2024): Brauer-Bund; Pale Ale; Reinheitsgebot).
For food law reasons, a best before date (BBD) must be indicated on a food product. In Anglo-American countries, the term "best before" is also frequently used. Many foods with an expired best-before date are thrown away, and supermarkets react to an approaching best-before date with discounts. If food that has passed its best-before date is still marketed, this can lead to legal problems, especially if it has gone off.
Is food that has passed its best-before date inedible or even harmful to health? Generally not, but of course it depends very much on the individual case, so ideally food should be consumed before the best-before date. However, everyone has probably opened a yogurt pot that has not yet expired and seen mold. In this case, something has gone wrong somewhere in the production chain, because mold is ubiquitous. Such errors are difficult to rule out completely, and we recently discovered that our bottle washer was no longer sucking up the alkaline detergent. A crack had formed in the silicone hose due to ageing and the suction was interrupted. We quickly noticed this by regularly checking our processes and rectified the problem immediately.
In this respect, the best-before date is always based on past experience, and for our bottled beer we specify a shelf life of 6 weeks from the day of bottling. The fact that beer can last more than 40 years in a bottle without any microbiological abnormalities was published in the trade journal BRAUWELT No. 20 (2020) 534 - 536. Although this beer, which was already 43 years old at the time, was no longer drinkable due to oxidation, no germs were found in it.
Basically, beer with a pH value of 4.5 and below is a microbiologically safe drink and germs cannot multiply in it. However, there are obligatory beer spoiling germs that can still spoil beer. These include lactobacillus brevis, which makes beer cloudy and sour, lactobacillus acetotolerans (sour smell) and pediococcus damnosus, which produces a buttery taste. Many of these germs are found on malt, which is why careful hygiene is required everywhere in the cold area. Hygiene in the brewing process is also discussed in our practical training and demonstrated in the brewery.
Before we started filtering beer, we never had to complain about an infection, and an official food inspection last year was also without any findings. A fundamental weak point is the counter-pressure filling system, the pipes and the bottles themselves. Deposits can form on edges and moving parts in the filling system, but we clean this equipment thoroughly with sterile water before and after filling and then extensively with wet steam. Our pressure drums are cleaned at 75 °C with an acidic cleaning agent, the dismantled fittings are cleaned with an alkaline cleaning agent at 63 °C, followed by a wet steam treatment. We pay meticulous attention to the cleanliness of the bottles by means of individual inspections, and since the introduction of an ordering system, all bottles are currently returned clean and rinsed. If they are then alkaline-cleaned for 7 minutes at 63 °C in the bottle washer and then rinsed with UV-treated water, they are technically sterile for brewing.
We have followed this meticulous procedure since the beginning of our brewery, and it doesn't seem to be that bad. An employee from a central institute at Clausthal University of Technology brought us back two empty bottles of beer on July 4, 2024, and the beer had been drunk a few days earlier. She assured us that the beer tasted very good and showed no signs of ageing. It had been forgotten in a fridge for almost two years and was only found again during an event. It was a dark beer brewed on June 18, 2022 as part of the brewing internship with an original gravity of 14.7 °P and 4.5% alcohol by volume and a wheat beer brewed during the same internship with only 0.9% alcohol by volume and 7.5 °P. A maltose-negative yeast was used for the latter, and the beer survived these two years without any problems and without any signs of fermentation by foreign yeasts. Hygiene is the be-all and end-all in food production, and an unfiltered and unpasteurized beer can survive two years in the fridge without any loss of quality.
At this point, we would like to report on our experiences with the filtration of beers and refer you to a five-part series in the trade magazine BRAUWELT, which was published there from No. 44 (2021) onwards, for basic details on filtration.
The first question that certainly arises is why a natural product such as beer should be filtered at all, as this removes the "good ingredients" and the beer loses quality, according to popular opinion. First of all, it must be taken into account that beer produced in large breweries is sold and exported in large quantities, that the vast majority of customers want a clear beer and that most of those who regularly read our website, like us, have certainly experienced the situation of beer standing outside the supermarket in the sun in summer and being offered at low prices.
Filtered and possibly pasteurized beer is a very robust beverage and can withstand such treatment for a while, but a naturally cloudy and perhaps unpasteurized beer would not survive such conditions for long without a massive loss of quality. On the other hand, at the now numerous events at Clausthal University of Technology, which we supply, we have noticed that there are quite a few people who have problems with brewer's yeast and show allergic reactions after drinking naturally cloudy beer, which can spread to the gastrointestinal tract. This is why we have started filtering beers in recent months and have implemented what is technically and financially feasible for us.
In medium-sized and larger breweries, the still quite cloudy beer is subjected to kieselguhr filtration approx. 3 - 6 weeks after the end of fermentation. This natural product adsorbs yeast and sediment and a large proportion of the sediment precipitates through sedimentation. The already relatively clear beer then undergoes fine filtration and, depending on the size of the brewery, candle filtration in the final stage. Candle filters are available down to a minimum pore size of 100 nm, and a sterile beer is obtained after such a filter. The filtration process can also be accompanied by pasteurization. There are other processes such as centrifugation with cross-flow filtration as well as layer and module filtration in one to several stages.
Apart from the space required, the technical and financial outlay is considerable and we quickly realized that such filtration was not feasible for us. Following discussions with colleagues from the brewing industry, we opted for cartridge filtration and use cartridge filters made of polypropylene with a pore size of 450 nm. For our filter housing and considering the costs and effort involved, these are the filters with the smallest pore sizes that we can use. The technical effort is rather low, we only need a carbon dioxide bottle to build up pressure, with which the beer is transferred from the pressure keg via the filter into another keg. We use a maximum of 3 bar overpressure, our flexible beer lines are designed for this maximum pressure, and the pressure difference at the filter is also subject to certain limits. The filtration of our beers generally works without any problems, and if the beer in the pressure keg has previously been well pre-clarified by natural sedimentation, 50 liters of beer can be filtered in approx. 20 minutes. However, if the beer is still clearly cloudy, the filter becomes so clogged after 20 liters that we have to rinse the filter with sterile water before filtration can continue. It can then take 90 minutes or more to filter 50 liters of beer.
Our experience can be roughly summarized as follows: When fermented with well sedimenting yeasts such as the top-fermenting "Nottingham", "BRY-97" or "Verdant IPA" from Lallemand Brewing or their bottom-fermenting "Diamond" (or the very widely used W34/70), the beers, when transferred to pressure kegs after the main fermentation is complete, are so well pre-clarified after about four weeks that filtration proceeds quickly and smoothly.* The filtration of 50 liters of beer then takes 20 - 30 minutes, and if the filter is then backwashed with 20 liters of sterile water, the filter is ready for the next 50 liters of beer.
However, the situation is completely different with poorly sedimenting yeasts, such as dust yeasts, and it can happen that the filtration rate becomes so low after just 10 liters that the filter has to be backwashed. This would be the case with Kölsch or Altbier yeasts and all yeasts whose sedimentation is classified as "low - medium" by the manufacturer. This also includes the "Windsor" from Lallemand Brewing. This yeast is negative for maltotriosis and is well suited to producing full-bodied Pale Ale beers with less than 2 % alcohol by volume using our isothermal high-temperature mashing process. However, filtration is rather unpleasant, which is why when we brew with this yeast, we either do not filter the beer at all or only filter small quantities for those who have problems with yeast. We now also indicate on our labels whether a beer is pasteurized and/or filtered.
Incidentally, the beers are apparently clear after filtration, we only see with a scattered light measurement that there are still minimal turbidities that pass through the 450 nm wide pores of the filter, we have not yet noticed any loss of taste, and the beer is effectively sterile after filtration because yeast cells and bacteria with a diameter of several micrometres are too large to pass through the filter.
However, there is one pitfall, and that is how the filter is handled and stored after filtration. We have received various pieces of advice. At a specialist conference in March 2024, it was recommended that the filters in the unopened housing should be counter-rinsed with cold water, then dried with 80 °C warm water and finally with carbon dioxide. We did this, and when we tried to filter a beer again after a week with such a filter, it tasted like cardboard. Even rinsing with 50 liters of water didn't help, the cardboard taste remained. We therefore disposed of the filter cartridge and fitted a new one. We were then advised to remove the filter cartridges after the last rinsing step and clean them in a diluted hydrogen peroxide solution. As with the cleaning with sodium hypochlorite solution, we obtained changes in taste in the filtered beer that went in the direction of cardboard. In total, we rendered five filter cartridges unusable in this learning process at a unit price of a good 50 euros - and disposed of them.
When we then asked the scene why this happens, we received all kinds of explanations and recommendations, including "We don't know anything about this!". Now, it may well be that the geometry of our filter housing played a trick on us, but we still had to find a solution, as these filters also incur acquisition costs. And as is often the case in the experimental sciences, a simple solution emerged. After the last filtration, the filter is rinsed with cold sterile water to remove most of the yeast cells from the filter fabric. We then fill the filter housing with the built-in filter cartridge with beer and store the filter hermetically sealed and under slight overpressure with carbon dioxide in our cooling chamber at 2 °C until the next use. When the next beer is ready for filtration, the filter is first rinsed with cold, sterile water and then filtered. So far, we have not noticed any changes in taste with this procedure, and we have already been able to filter a good 500 liters of beer with the current filter cartridge. The next filtration will be accompanied by a microbiological analysis. As the beer is effectively sterile after filtration and we only use sterilized utensils and sterile UV-treated water for counter-rinsing, we don't expect any unpleasant surprises, but as we all know, the devil is a squirrel and a check can't hurt.
We won't be filtering all beers in future because of the effort involved, especially as the turbidity of the beer depends not only on the yeast, but also on the brewing malt and the hops used. However, we will filter the bottom-fermented beers fermented with Diamond or W34/70 and the top-fermented pale ales fermented with BRY-97 or Nottingham, as well as our non-alcoholic beers produced with maltose-negative yeasts. Pale ale beers, which are sometimes even expected to be cloudy by consumers (-> Hazy IPA), will only be filtered in small quantities for those who have problems with yeast in beer.
* We mainly use yeasts from Lallemand Brewing, which we buy in stores at normal prices, and now only use a few varieties. We have continuously improved our brewing process since our brewery was founded and have developed a certain modesty along the way. Of course, there are also excellent yeasts from other producers, and from time to time we also experiment with other yeasts. However, for our scientific work and to ensure a certain continuity, we only use a few different yeasts, most of which have very good sedimentation properties, plus maltose-negative yeasts, which we obtained from Priv.-Doz. Dr. Mathias Hutzler from the Center for Brewing and Food Quality at the Technical University of Munich in Freising/Weihenstephan.
On 26 June 2024, our reverse osmosis plant was put into operation, which now supplies us with demineralized water at a flow rate of approx. 1.8 l/min.
For almost a year now, the surface water in Clausthal-Zellerfeld has been treated by the municipal utilities in two new waterworks, and in addition to filtration and treatment with ozone, calcification with calcium dihydrogen carbonate is practiced. By increasing the pH value, the municipal utilities hoped to reduce corrosion in the municipal pipe network and among end consumers....
The tap water now has an annual average water hardness of 5 - 6 °dH (previously: 1 - 2 °dH) and is still considered soft, even if you can now see clear traces of limescale on the taps (and not only there). Water hardness is subject to certain process-related fluctuations, but these are completely unproblematic in terms of food safety. However, the mineral content influences the brewing process at several points and very soft water is essential for brewing light-colored beers, especially Pilsner beer.
Not only the total hardness and the so-called residual alkalinity play a role here, but also the content of calcium ions, which influence the wort break, the sedimentation of the yeast and also the hop aroma. The last authentic Pilsner beers we produced were around November/December 2023, around February/March 2024 we realized that there was a problem, and after incorrectly selected hop batches could be ruled out as a source of error, only the brewing water remained as a source of error. For a few weeks now, we have been able to determine the total hardness of the water in the brewery, and in the last few days before the reverse osmosis system was installed, it was around 6 °dH.
As expected, the reverse osmosis water has a measured total hardness of 0 °dH. The so-called residual alkalinity, which ultimately describes the relative reduction in the pH value when mashing malt grist, is primarily influenced by the concentrations of hydrogen carbonate and the cations of calcium and magnesium. Calculators can be found on the Internet for this purpose, and if the total hardness is known as well as the so-called acid capacity up to pH 4.3 (often shown as such in water analyses), the residual alkalinity can be calculated using the concentrations of the ions mentioned. This can be positive or negative, as it ultimately only describes whether the pH value of the mash drops more or less after mashing. According to current planning, this topic will be covered in a double lesson in the "Beer Analysis" lecture in the coming winter semester.
As all of our recipes are based on a water hardness of 1 - 2 °dH, we will set the water hardness to approximately 1 °dH in the upcoming brewing trials. To do this, we have to determine the total hardness of the water on a daily basis and then mix it with the reverse osmosis water depending on its hardness. With a total hardness of 6 °dH, we achieve a total hardness of 1.2 °dH with a mixture of 80% reverse osmosis water and 20% tap water. If, for example, we had a total hardness of 12 °dH in the tap water on one day, we would have to mix our brewing water from 90% reverse osmosis water and 10% tap water and would also achieve 1.2 °dH. At the beginning of June, an external laboratory determined our water to have a total hardness of around 3 °dH, and in this case the proportion of tap water would have to be 40%. There are water treatment systems that set the specified values automatically, but the purchase costs are also considerable if a high throughput is required, and there is also a certain amount of maintenance.
One disadvantage of our system is the low throughput of just 1.8 l/min, which we could only increase by using a second system in parallel. Filling only 260 liters of brewing water (including tap water) now takes a good 2 hours, during which you have to check every now and then to make sure the boiler isn't overflowing. In addition, the hardness of the tap water has to be determined in the laboratory before it is added, as there have definitely been fluctuations in the past. Unfortunately, the effort involved is noticeably higher than before, but this way we can mix our brewing water in a defined way and brew reproducibly again, which is an essential prerequisite for scientific work. Around September, we should be able to brew authentic Pilsner beers with a maximum alcohol content of 2.5% vol. from our brewery again. On July 2, we will resume brewing operations and brew two non-alcoholic beers (60 liters each) with a maximum of 0.5% alcohol by volume due to the high demand. On other brewing days, we will brew an alcohol-free pale ale, a pilsner for "Tank Siegfried" and a pale ale with less than 2% alcohol by volume for "Tank Volker". We will report on these brewing trials.
Those of you who regularly read our website will have noticed that we have been having problems adjusting the bitterness of our beers, especially the pale ones, for several months now. Even a Pilsner, as we were able to brew last year, with 2.5 or 5 % alcohol by volume, is not possible at the moment. The beers are good, but they no longer taste like they used to, and our Pilsner is no longer authentic either. Initially, we hoped that the hops supplied in small packs were simply mislabeled, but this assumption proved to be wrong when the same problem occurred with the hop extract from a major American and well-known manufacturer - unfortunately, because the solution to this problem would have been very simple. So what is the cause of these problems?
Without going into the complex interrelationships in depth, beer from Pilsen in the Czech Republic is so unique because the water there is naturally very soft. Water hardness is essentially determined by magnesium and calcium ions, and a distinction is made between carbonate hardness (which leads to limescale deposits, particularly on heating elements, and not just on household appliances) and non-carbonate hardness. Both of these metal ions influence the brewing process at different points. A higher proportion of calcium ions in particular is more beneficial for the mashing process, but the wort brew also benefits, as does the clarification of the finished beer. However, the hop yield suffers as a result, and the typical pilsner aroma is also affected by an excessively high proportion of calcium and/or magnesium ions.
Without pre-empting upcoming discussions at this point, we are really struggling with the limescale treatment of tap water by the municipal utilities, who hoped that this would reduce the corrosion problem in the municipal water supply network. The fact that limescale deposits are now also being observed in private households may only be a blemish, as the humic substances that used to precipitate reddish from the high moor water are now being filtered out in the two new waterworks. However, we have more than clear evidence that the lime content is subject to strong fluctuations, even if an annual average of 5 - 6 °dH is still considered "soft water".
But what is an average value? If a car manufacturer specifies that all 4 tires must be inflated to 2.5 bar, then each tire should also be inflated to 2.5 bar. If, for example, the front left and rear right tires only have 1.5 bar each and the others 3.5 bar each, the mathematical mean value would also be 2.5 bar, so superficially everything would be fine in relation to the mean value. However, you shouldn't expect a vehicle to be safe to drive with such differently inflated tires. And it's similar here with the average hardness. Sometimes we have very soft water, which we can see from the negligible traces of limescale on the taps, and sometimes we have to go to great lengths to remove the limescale. For the brewing of beer and especially for our research work, water that is unquestionably flawless and very good in terms of food technology despite fluctuations in the limescale content is a major problem. What can we do, because we can't brew like this, at least not reproducibly and certainly not according to scientific criteria.
Most large breweries have water treatment plants because of the same problem. In a nutshell: The tap water is demineralized to a limit value of dissolved salts via a so-called reverse osmosis system (distilled water would be demineralized). Such water is very soft and could, in theory, be used for brewing Pilsner beers. In practice, however, the demineralized water is either salted back to a defined low hardness level automatically, or tap water is added on a daily basis. The latter procedure requires daily analysis, but determining the water hardness via titration is not a fundamental problem for a laboratory.
The costs for reverse osmosis systems are highly variable, and we have received a detailed but not exactly inexpensive quotation from a specialist company. For various reasons, it can take several months before this technical option is implemented. We have therefore decided to buy a simple reverse osmosis system and then mix our brewing water from this and the tap water on a daily basis. All of our tried and tested recipes, which we are constantly developing, are based on the previous water hardness of 1 - 2 °dH, and that's where we want to go again. Out of curiosity, we will certainly brew a pilsner with pure reverse osmosis water, i.e. with demineralized water. Malt enriches the salt content of the finished beer anyway due to the minerals it contains, and we'll see what happens. However, we certainly won't be making 200 liters of beer in such an experiment. The reverse osmosis system we ordered only has a low throughput of a maximum of 2 l/min, and we will also have to add tap water on a daily basis, but this makeshift solution will help us get by for the time being. Brewing operations are largely suspended until this system is installed, so the next report on a current beer is not expected for at least four weeks. We hope that we will then be able to offer Pilsner and Helles in the quality we were used to in the winter semester, naturally with a maximum alcohol content of 2.5% vol.
In this section, we would like to report from time to time on the observations we make in the everyday life of a research brewery, most of which will also be found in one way or another in larger breweries. On this occasion, we would like to report a little about the problem of moldy bottles. When you buy a crate of beer in the supermarket, you generally don't think about what happens to the empty bottle. With a few exceptions, the bottles are left unwashed in the crates until the crate of empty bottles is returned to the brewery via the deposit system, which can take several weeks.
There, the bottles are pre-sorted and rinsed in a technically sophisticated bottle washer with hot caustic solution and under considerable pressure, and the crate itself is also cleaned. After a rinsing step with water, most of the bottles are then sparkling clean on the inside and technically sterile, ready to be filled with the next beer. Before this, they are x-rayed with light, and bottles with defects that are not necessarily visible but still present are automatically sorted out. In very dirty bottles, however, it can still happen in rare cases that such a bottle falls through the grid and is filled with beer. It is also possible - and there are specialist articles on this - that a heavily moldy bottle may still have a thin layer of mold on the bottom after cleaning, which is barely visible to the eye and can ultimately only be removed using chlor-alkaline. It would go beyond the scope of this article to go into this in detail.
But why does mold actually form in unrinsed beer bottles, even if a perfectly clean bottle has been filled with beer in the brewery? Mold fungi and spores are ubiquitous, in technical jargon this is called "ubiquitous". We know this from the household. You leave fresh bread in the bread bin and at some point it starts to go moldy. I'm sure everyone has bought fresh fruit, put it in the fridge and after a few days you find mold on the fruit. This happens very quickly with raspberries or strawberries. Or, you open a pot of yoghurt and there is mold on the edge of the pot.
Most molds are aerobic, i.e. they need air to grow, but some species can also gain energy through fermentation if they are excluded from the air. In addition to carbohydrates, which are broken down into simple sugars by amylases, molds also need proteins or amino acids and, of course, water to grow. All these nutrients are found in food and therefore also in beer. It is therefore inevitable that molds from the environment will settle in a beer bottle. If the bottle is well rinsed, the molds will not find a nutrient medium, and air and water alone will not allow them to grow. However, beer contains unfermented sugars, proteins from the foam and also water. The small amounts of alcohol in the beer do not interfere significantly, and sometimes acetic acid bacteria also find their way into an unrinsed bottle, which oxidize the alcohol to acetic acid in the presence of oxygen. As a rule, however, the molds are there first, and these begin to multiply in the perfect nutrient medium that they find in an unrinsed bottle.
As we are not allowed to sell beer as a university or selling it would be very complicated under tax law, we give it away free of charge. Feedback is very important to us, as we are constantly researching and developing new recipes. We rarely brew a beer exactly the same as the last time, and even with the regularly brewed pale beers or pale ales we vary the malt blend or hop varieties a little. Feedback from our "test drinkers" is important to us, and if someone tells us that you can't tell when drinking that our beers only contain half as much alcohol as beers with twice the alcohol content, then this helps us on our way.
We have a high-pressure bottle washer for cleaning our bottles, which cleans the bottles in around 8 minutes with 63 °C warm suds. Very rarely do we have to clean a bottle a second time. We limit ourselves to simple alkaline solutions because of the unpleasant odor and do not use chlor-alkaline solutions (which is also better for the environment) in this machine, which we can currently only use to clean 0.33 L and 0.5 L bottles, with a maximum of 0.75 L bottles.
We have a conventional dishwasher with a "bottle fairy" for the 1 L bottles, which we have mainly dispensed so far, which we operate with lye; we can clean 20 1 L bottles in an almost 3-hour wash cycle. This machine is only suitable for light soiling, mold cannot be removed and the materials of this machine are not suitable for chlor-alkaline detergents. In addition, the pump does not build up enough pressure to reliably remove mold from bottles.
We have therefore had no choice but to take a close look at every single 1 L bottle and clean moldy 1 L bottles by hand. Even thin layers on the bottom that are barely visible to the naked eye require manual cleaning. To do this, either each individual bottle is filled with a chlor-alkaline solution, sealed and shaken, with an exposure time of one hour. Each bottle is then rinsed by hand and cleaned in the dishwasher with lye at 70 °C. Alternatively, we use our manual barrel washing machine, which cleans each individual bottle under high pressure at 75 °C with an acidic cleaning agent, which takes approx. 5 minutes per bottle. Cleaning with alkaline agents is not possible due to the unavoidable formation of aerosols in the air we breathe. After the bottles have cooled down, they are rinsed with cold water from our water treatment plant; our tap water is effectively sterile. It takes around 2 hours to clean just 20 moldy bottles, and there is really nothing else that can be done during this time because individual cleaning, especially with the drum washing machine, requires supervision.
The label on all our bottles contains instructions in contrasting colors to rinse the bottles 2-3 times immediately after emptying. We have empirical values, and if this is followed, there is no mold growth in these rinsed bottles. We have tested this umpteen times, which is why we write this on the labels. Despite this, around 15% of the bottles have always come back moldy, even when we were told to rinse the bottles when they were handed out. On a trial basis, we omitted the warning on these bottles, after which 95% came back moldy. It doesn't help us if the moldy bottles are rinsed before they are returned, we can see the thin layer remaining at the bottom of the bottle with the naked eye. We once burst an apparently flawless bottle during filling, and it was only because we were wearing protective equipment that nothing happened to us. One possible cause is that the bottle was cleaned with boiling water to remove the mold before it was returned to us. This creates invisible tension in the material, and a bottle can then burst without warning. Even an automatic system in a large brewery would not be able to safely sort out such a bottle.
We thought long and hard about how to deal with this problem, as we can do no more than ask the bottles to be rinsed out immediately after emptying. As a first measure, we have discontinued the free distribution of beer in 1 liter bottles for an indefinite period. Of course, we will continue to offer beer in 1 liter bottles to take away, but these must be explicitly requested from the office. We trust that our request to rinse the bottles immediately after emptying them will be implemented in this way.
We will continue to fill beer crates for events, e.g. for the TU Clausthal Big Band. We will also continue to dispense beer in kegs. There is a negligible risk of mould here, and we are well equipped to clean and steam sterilize kegs. As a further measure, we will consider how we can expand our high-pressure bottle washing machine so that we can also reliably clean 1 l bottles, or we will switch to 0.75 l bottles. To do this, we will have to ask the manufacturer and, if possible, convert the machine at great expense, and we will have to try out with mold test bottles how many rinsing cycles we need to reliably clean the bottles. We will also have to test whether the simple alkaline detergent is sufficient or whether we need to use a chlor-alkaline detergent (which we would actually like to avoid for the sake of the environment). Ultimately, we are subject to food controls and, as a research brewery at a university, it is our duty to ensure that our beer is only filled into perfectly clean bottles.