Attenuation
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Attenuation literally means "reduction in quantity". Yeast (or other microbes) progressively attenuate the fermentable sugars during fermentation. Measuring this attenuation is important for monitoring fermentation process, and it allows us to calculate the alcohol level. Brewers generally measure and refer to "apparent attenuation" rather than the real attenuation. As yeast ferments wort the simpler sugars are partly converted into ethyl alcohol and carbon dioxide, and the specific gravity of the mixture progressively declines until fermentation is complete. [1]
- Apparent attenuation
- The degree of fermentation as measured by a hydrometer without alcohol corrections[2]
For beer, attenuation should typically be in the range of 78–85%, depending on the style.[3] Wine generally will attenuate over 100%.
Actual attenuation is roughly about 20% higher than apparent attenuation.[2][3]
Caramelization and Maillard reactions occurring during wort boiling have a small impact by removing fermentable sugars.[3]
Mashing-in above gelatinization temperature will result in a highest attenuation. Due to the low thermostability of β-amylase, mashing-in at 45°C or 52°C may already result in partial inactivation of β-amylase, thereby impairing starch conversion. Therefore, it is important to mash-in above gelatinization temperature, resulting in shorter mashing processes.[4]
Unfermented sugar in beer adds to both perceived body (palate fullness) and sweetness.[5] It is well-known that sweetness masks flavors, and therefore the residual sugar resulting from a low attenuation will mask other flavors in the beer such as the malt and/or hop characteristics.
Milling conditions do not appear to significantly influence attenuation, despite higher levels of extractable enzymes.[6]
Low-attenuation beers are more susceptible to certain spoilage microbes (see Contamination).[7][citation needed]
The fermentability of the wort is not only determined by the availability of fermentable sugars in the wort but also the content of amino acids and other nutritional components required for yeast vigour and biomass production.[8]
References
- ↑ Briggs DE, Boulton CA, Brookes PA, Stevens R. Brewing Science and Practice. Woodhead Publishing Limited and CRC Press LLC; 2004.
- ↑ a b Fix G. Principles of Brewing Science. 2nd ed. Brewers Publications; 1999.
- ↑ a b c Pahl R, Meyer B, Biurrun R. Wort and Wort Quality Parameters. In: Bamforth CW, ed. Brewing Materials and Processes: A Practical Approach to Beer Excellence. Academic Press; 2016.
- ↑ De Rouck G, Jaskula B, De Causmaecker B, et al. The influence of very thick and fast mashing conditions on wort composition. J Am Soc Brew Chem. 2013;71(1):1–14.
- ↑ Kunz T, Reinhardt Ch, Eon-Jeong L, Dörr T, Radowski A, Methner FJ. Impact of fermentable and non fermentable carbohydrates on the sweetness, improvement of palate fullness and SO2-content in beer. BrewingScience. 2012;65(11):140–149.
- ↑ Sissons M, Taylor M, Proudlove M. Barley malt limit dextrinase: Its extraction, heat stability, and activity during malting and mashing. J Am Soc Brew Chem. 1995;53(3):104–110.
- ↑ Sacher B, Becker T, Narziss L. Some reflections on mashing – Part 2. Brauwelt International. 2016;6:392-397.
- ↑ Evans DE, Li C, Eglinton JK. The properties and genetics of barley malt starch degrading enzymes. In: Zhang G, Li C, eds. Genetics and Improvement of Barley Malt Quality. New York: Zhejiang University Press, Hangzhou and Springer Verlag; 2009:143–189.