High gravity brewing

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The use of high gravity wort (16–18°Plato) has become common practice in many commercial breweries. High gravity wort allows a lower volume of wort to produce the same amount of beer. This leads to increased production capacity, with benefits including reduced energy input and reduced labor, reduced cleaning and waste costs and, possible improvements in beer flavor. Pilot-scale trials have demonstrated the feasibility of fermenting very high gravity (VHG) worts (20–25°P) without major detriment to beer flavor characteristics, although fermentation does suffer.

Overproduction of esters typically occurs during high gravity fermentation.

High gravity brewing has been progressively introduced into many breweries, worldwide, due to the economic advantages it has over the use of normal gravity worts. However there are certain drawbacks to such a process which include: decreased material efficiency; reduced foam stability; a problem with flavour matching and perhaps most importantly, high gravity brewing can exert a negative effect on yeast performance. This last drawback is due to three inter-related factors: an increased ethanol concentration; increased osmotic stress and finally, the effect of nutrient limitation.

It is important that the calcium content of dilution water is not higher than the calcium content of the concentrated beer to be diluted, in order to avoid oxalate precipitation. There are also strict requirements regarding oxygen content, which should mainly be less than 20 ppb, and THM levels are also of great importance. Some breweries distinguish between brewing liquor and dilution liquor in terms of levels of THMs permitted, though others do not. The microbiological composition of the dilution water is very important as this water is not necessarily boiled. Treatment with a proper disinfection system and a UV (ultraviolet) system prior to use is indispensable.

Dilution water is similar to brew water, as it also results in the product, but in contrast to brew water, special attention has to be paid regarding a low Ca2+ level. Any increase in the Ca2+ level in the filtered beer will affect the Ca-oxalate equilibrium, increasing the risk of the formation of Ca-oxalate crystals, which can finally lead to an unwanted increase in beer gushing tendency. As the major amount of the Ca2+ from the brew water is utilized during the course of the production process (in mashing, lautering, cooking and fermentation), the Ca2+ level in the dilution water should be low, at least below the level in the beer being diluted. The risk of Ca-oxalate precipitation can be assessed based on the calcium and oxalate concentration. Schur et al. (12) proposed a corresponding formula including recommendations of target ranges. The dilution water must also be deaerated in order to avoid beer oxidation. The common target value for deaeration plants nowadays is <10 ppb dissolved oxygen. As dilution water goes directly into the final product without any further treatment steps, THMs must be reduced even further, compared with brew water, with a target of <1 ppb.