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Drinkability is the key
The key to the enjoyment of a light lager lies in its drinkability, which in turn is made up of numerous factors.
All aspects that contribute to the quality of a light lager result directly from the respective brewing technology, from the brewhouse work to yeast management, the management of fermentation, maturation and storage through to oxygen-free filtration and bottling.
In the brewhouse, many different factors determine the quality of a light lagerKey factors in the brewhouse
The malting process itself, with its resulting malt fractions and possible oxidation, has an impact on a number of quality aspects such as tannin and ageing stability.
Water treatment is particularly important for light lager beers, as it influences both the colour and the quality of the tannins.
The mashing process with the mashing temperature and temperature rests must be adapted to the malt quality. Avoiding any oxygen absorption is crucial for the subsequent flavour stability and the quality of the tannins.
The shortest possible lautering process prevents undesirable leaching of the husks. The correctly coordinated boiling process influences the foam stability and colloidal stability.
Ideally, a wort for a Helles should have a FAN content of 180–200 mg/l in order to provide sufficient yeast nutrition, minimise the formation of higher alcohols and avoid subsequent oxidative degradation of the amino acids in the filtered beer. Finally, a pH value of 5.0–5.2 should be aimed for in the wort for a lean character and better flavour stability.
A decisive key to good flavour and foam stability lies in yeast management and fermentation controlYeast management and fermentation technology
The aim of good yeast management is to prevent the release of quality-reducing substances from the yeast cell. Brewers refer to autolysis products, such as fatty acids, amino acids and proteinase A, which breaks down foam-positive protein fractions.
The release of these substances by the yeast into the beer takes place both through autolysis (which occurs rather rarely), in which the yeast dissolves the cell wall, and through stress excretion, which is clearly the more decisive factor.
The condition and age of the yeast cell determine the potential for the release of undesired autolysis products. The older the yeast cell becomes, the more of these products it accumulates in the vacuoles. Furthermore, the tendency to stress excretion and autolysis increases with the age of the yeast cell.
As the yeast cell ages, its size, weight and tendency to flocculate also increases. Young yeast cells remain in suspension for much longer and are therefore more fermentable. The tools for rejuvenating the yeast population lie in aerobic yeast propagation, sufficient aeration of the wort (8 mg O2/l), not pitching the harvest yeast too frequently and very generous shotting down of the yeast during yeast harvesting.
Harvest yeast should be shot down generouslyHarvesting and storage of bottom-fermenting yeast
When harvesting bottom-fermenting yeast, it should be noted that usually only flocculated and therefore older, heavier and less active cells settle in the conus of a tank and can therefore be harvested. Most active (small and light) yeasts, on the other hand, remain in suspension. The activity therefore decreases with each harvest cycle and the tendency to release autolysis products increases.
When storing a harvested yeast, it should be noted that the activity decreases drastically with storage time while the tendency to autolysis increases significantly.
As with fresh fish, the motto should be: as short as possible (1–3 days) and as cold as possible (0–2 °C). It should also be borne in mind that viscous yeast in a tank cannot be cooled like normal liquids. This is due to its viscosity and insulating properties. Cooling in the tank can only be achieved by stirring or pumping or by cooling during transport from the fermentation tank to the yeast storage tank.
Pitching actually just means „adding the yeast to the wort“ – but it’s not that simple and there are some details to considerPitching the wort
As new young and therefore active yeast cells are only formed under aerobic conditions, sufficient aeration of the wort is crucial for the quality of the beer. Depending on the temperature of the wort, the value for oxygen saturation is 7–9 mg oxygen per litre. As yeast cells can be active only in suspension, the yeast must be completely suspended. Yeast that is at the bottom of the tank after pitching will never go back into suspension, but will directly start stress excretion or even autolysis.
With regard to the preparation temperature, it should be noted that 80 per cent of higher alcohols are formed during the aerobic phase. As the higher alcohols are direct precursors for ageing carbonyls, a low pitching temperature is crucial for flavour stability. For this reason, the uniformity of the pitching temperature is an important factor for the quality of the beer. In addition, attention must be paid to the yeast cell count and its uniformity during pitching, as both the formation of esters and SO2, which is so important for flavour stability, depend on it. Fewer yeast cells mean more ester formation and a better ratio of esters to higher alcohols as well as an increase in the SO2 content. Depending on the yeast activity, the aim is a yeast cell count of 8–12 million cells/ml. Of course, the pitching yeast used should have very good viability (>95 %) as well as vitality in order to minimise the tendency to autolysis.
The maturation phase is particularly important for bottom-fermented beers, as many processes that are important for beer quality are finished hereMaturation of the beer
After a rapid start of fermentation with a pH drop to around 4.4, the focus is on the complete maturation of the lager beer. Due to the traditionally low fermentation temperatures, fermentation must be followed by a maturation phase, as many processes that are important for beer quality have not yet been completed. The so-called young beer bouquet substances must be converted by the yeast. Diacetyl serves as a perfect indicator of the progress of maturation by the yeast. However, before the yeast can reduce the flavour-active diacetyl into the flavour-active 2,3-butanediol, the precursor product 2-acetolactate formed by the yeast must be converted into diacetyl by chemical decarboxylation.
This chemical reaction as well as the reduction by the yeast are dependent on the temperature. A minimum temperature of 5 °C is therefore necessary for maturation. Cooling the green beer too quickly to lager cellar temperatures and thus insufficient maturation is one of the most common mistakes in lager beer production.
In addition to the refinement of the beer flavour through the transformation of young beer aromas and the expulsion of volatile (sulphur) compounds through CO2 washing, the extensive fermentation of the residual extract and the achievement of the theoretical final degree of fermentation is an important factor for drinkability and therefore quality. As all the processes involved in maturation are carried out by the yeast, the activity of the yeast in this phase is decisive and explains the advantages of the riddling technique.
A long, cold storage phase is advantageous, as the CO2 gets better integrated and the foam stability increasesCold storage
After maturation, cold storage begins, which is not directly dependent on the yeast. On the contrary, an excess of yeast in this phase would be counterproductive. A small amount of active yeast cells in suspension – without yeast sediment – would be ideal, as the active yeast in suspension further reduces the beer through its reducing power and thus optimises it towards freshness, without the negative effects of a tendency to autolysis in the yeast sediment. As far as possible, regular shotting off of the yeast as well as yeast removal during a tank change or the use of a green beer centrifuge is desirable. The optimum temperature during this phase is 0°C to -1.5°C. If the above factors are present, a long or even very long cold storage phase is absolutely advantageous for the quality of the lager beer, as the CO2 is increasingly better incorporated, further improving both the foam stability and the mouthfeel.
The last two stages of the production chain are crucial for the freshness and flavour stability of a light lagerFiltration and bottling
The most important factor for quality during filtration and bottling is the avoidance of any oxygen pick-up. Starting with the emptying of the storage tank by CO2 via the beer transfer to the filter (mechanical seals!), filter venting and an oxygen-free diatomaceous earth dosage. Acid cleaning of pressurised tanks in a CO2 atmosphere without opening the tank is now state of the art. This is followed by an O2-free beer transfer to the filler (mechanical seals!) and the filling process itself.
At the very end, it then depends on a perfectly adjusted and flawlessly functioning high-pressure injection system to get the perfect light lager in the bottle.
Despite all the art of brewing and state-of-the-art technology, the most important point for the quality of a light lager is after it has been bottledFreshness is the most important factor
Due to the separation of the yeast during filtration and the resulting lack of reduction potential, there is hardly any protection against oxidation in the bottled beer. Depending on the quantity of precursors for ageing components and the residual oxygen, oxidation and a reduction in freshness inevitably occur. But this is exactly what quality depends on. Depending on the temperature, this unavoidable loss of quality is not in the range of months like the MHD, but in the range of a few weeks.
The article is based on an article published in BRAUWELT No. 3, 2024.
