This page is fully or partially automatically translated.
Make an appointment with
So that you can make an appointment, the calendar will open in a new tab on the personal profile of your contact person.
Create an onsite appointment with
So that you can make an onsite appointment, the appointment request will open in a new tab.
Brewing yeast of the future
The Research Center for Brewing and Food Quality (BLQ) at the Technical University of Munich has been offering its world-renowned bottom-fermenting yeast strain Saccharomyces pastorianus Frisinga - TUM 34/70 in a novel frozen format since December 2021. This frozen yeast product is called SmartBevTM Lager TUM 34/70 and was developed and validated for brewery use in collaboration with Chr. Hansen, Hørsholm, Denmark.
The use of this yeast enables breweries to save the entire yeast production in the laboratory and to start it microbiologically pure directly in the propagator or fermentation tank.
Package containing 1 kg of frozen yeast, which is frozen at - 60 °C, storable and has a cell density of > 1 billion cells per mlTUM 34/70 - a global citizen
Over 90 percent of the world's beer production is bottom-fermented beer, which is made with bottom-fermenting yeasts of the Saccharomyces pastorianus species. The cold fermentation properties of bottom-fermenting yeast ensure that the yeast forms low concentrations of fermentation byproducts when fermented at low fermentation temperatures and, in combination with a high degree of fermentation, thus produces neutral beers with high drinkability.
The best-known and most widely used bottom-fermenting yeast strain in the world is Saccharomyces pastorianus Frisinga - TUM 34/70. In his 1956 dissertation, Prof. Ludwig Narziß characterized this yeast as a strain with excellent fermentation properties and a balanced aroma profile. Since then, the yeast TUM 34/70 started its worldwide triumphal procession and is used in breweries in almost every country in the world.
Yeast cultivation in the laboratory: a full-time job
The aim of yeast purification in the laboratory is to produce yeast in as active and microbiologically pure a state as possible up to the required preparation volume. Depending on the process, this laboratory pure culture takes approx. 3 - 7 days and comprises many individual steps. One of the challenges is to ensure that the laboratory pure culture is microbiologically pure and highly active at the time of inoculation. Even with the highest microbiological working standards, there is always a residual risk of laboratory contamination of the pure yeast.
If the brewery laboratory itself maintains a yeast culture as a slant agar, it must be made from wort with sufficient nutrients and inoculated every 4 - 6 weeks and stored at 2 - 4 °C.
Application steps (withdrawal, thawing, aseptic transfer, propagation) until yeast is added to initiate fermentation (total time until preparation 2 - 3 days, preparation time 1 h)TUM 34/70 goes frozen
The simple application steps of the frozen bottom-fermented yeast SmartBevTM Lager TUM 34/70 are shown in the adjacent figure. The yeast can be stored at - 60 °C for up to 18 months (minimum shelf life).
For this type of storage, a special - 60 °C freezer is required, which is available in different volume capacities. Costs for this one-time investment are between approx. 1200 and 2000 EUR net, depending on the storage space (10 - 150 packages). Before the yeast can be used, it must be thawed in a container with water (e.g. 30-liter bucket) for about one hour. The frozen yeast liquefies during this period. The liquid yeast suspension can be aseptically pierced in the bag via a septum. There are already two different aseptic transfer systems on the market. Now the liquefied yeast can be pressed into the line or into a vessel and the propagation can be started. At a dosage of 1 kg yeast per 10 hl wort, propagation takes approx. 2 - 3 days to reach a cell density of 80 - 100 million yeast cells per ml in the propagator (depending on temperature, aeration interval and circulation of the yeast suspension). Subsequently, the propagation yeast can be used to start fermentation. Recommended numbers of pitching cells for a rapid start of fermentation are between 10 and 20 million yeast cells per ml.
Microbiological specifications
The basic prerequisite for perfect propagation and fermentation is a microbiologically pure propagation yeast and, consequently, a microbiologically perfect pure culture yeast.
Each batch of propagation yeast is tested for microbiological contamination such as foreign yeasts, wild and over-fermenting yeasts, and bacteria. Only after a batch of SmartBevTM Lager TUM 34/70 meets all these specifications is it released for use. In addition, the yeast is also tested for relevant food pathogens, and yeast vitality and viability are also tested.
Evolution of yeast cell concentration per ml (blue bars) and percentage of dead cells in the yeast population (white dots) over the time course of 2 days after inoculationPropagation application
The use in propagation - here on a 30-hl scale - is illustrated in the adjacent figure. The graph shows the rapid decrease in the percentage fraction of dead cells (white dots). It should be noted that this measurement used the intercalating dye propidium iodide to stain dead cells, which detects higher dead fractions compared to the methylene blue method. This means that if the same measurement were performed with methylene blue, the measured values would be even lower. The dead fractions were below two percent on day 1 and 2 of propagation.
In addition, the blue bars show the expected increase in yeast cell concentration, which in this case corresponds to an approximate 25-fold increase in yeast population within 48 h.
The yeast can be used for pitching after 48 h or, if necessary, propagated a little longer if even higher cell densities are required for pitching (depending on the wort pitching volume). The application in propagation can be adapted to the specific operation in order to use the required yeast cell concentration with high activity for pitching.
Beer quality with the use of harvest yeast
In addition to the use of propagation yeast, the use of harvest yeast is an important process and economic factor. Sensory tests according to the DLG tasting scheme of bottom-fermented beers produced with the propagation yeast of the BLQ and the harvest yeast of the 1st run and the 3rd run derived from it showed a high sensory acceptance, all sensory characteristics were 4.3 or above (with 5 as maximum) according to the DLG scheme.
Chemical measurements of fermentation byproducts (young bouquets and bouquets) were within a small range of variation, reflecting the basic sensory comparability of the beers. The young bouquet substances (e.g. diacetyl and acetaldehyde) were reduced by the yeasts of the different guides to such an extent that they had no negative sensory effects (keyword off-flavor) on the beer. In summary, the use of propagation yeast and the resulting harvest yeasts allows beers of sensory high quality to be produced reproducibly, with the brewery saving itself the complete laboratory purification and the associated risk of contamination.
Acknowledgement
The author would like to express his sincere thanks to Nathalia Edwards and Karsten Laurents for the fruitful cooperation with Chr. Hansen, Denmark, and the brewmasters Bernhard Löw and Martin Poschner, both of Brauerei Wieninger, Teisendorf, for the long-term testing of the yeast and the practical implementation.
