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]
Typically, brewers do not seek to produce worts that have maximal fermentability, because unfermented dextrins and limit dextrins can influence beer mouth-feel and other quality characteristics (6,45).[9] Cites Bamforth, C. W. Beer flavor: Mouthfeel. Brew. Guard. 130:18-19, 2001. and Langstaff, S. A., and Lewis, M. J. The mouthfeel of beer—A review. J. Inst. Brew. 99:31-37, 1993.
To control fermentability in the face of variations in malt quality or even unexpected mash behavior resulting from the deficiencies of traditional predictors of fermentability such as DP (25), brewers typically adjust either mash temperature or mash duration. Shorter mashes are an effective option to reduce fermentability but come at the cost of a small proportion of extract (22). Increasing temperature is also an effective measure to reduce fermentability. Obviously, with the malts containing the Sd2H beta-amylase thermostability type, this effect will not be as large as for Sd1 and Sd2L malts. In addition, there is the potential cost of slightly reduced extract and reduced FAN. Other normally unmeasured consequences also result from increasing mash-in temperature in the form of reduced maltose/glucose ratio (20), the level of total fatty acids, and the level of C18:2. Both the maltose/glucose ratio (58) and the level of C18:2 (51,57) can alter final beer flavor, and the level of wort lipids per se can substantially impact yeast fermentation performance (7,41).[9]
Two different worts with the same s.g. can have very different levels of fermentability due to the difference in sugar composition.[10]
Henson et al., (2008) provided evidence that higher solute concentrations in the mash improves fermentability.[8]
- Henson, C.A., and Duke, S.H., (2008) A comparison of standard and nonstandard measures of malt quality. J. Am. Soc. Brew. Chem., 66: 11-19.
References[edit]
- ↑ 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.
- ↑ a b 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. Springer; 2010:143–189.
- ↑ a b Evans DE, Goldsmith M, Redd KS, Nischwitz R, Lentini A. Impact of mashing conditions on extract, its fermentability, and the levels of wort free amino nitrogen (FAN), β-glucan, and lipids. J Am Soc Brew Chem. 2012;70(1):39–49.
- ↑ Muller R. The effects of mashing temperature and mash thickness on wort carbohydrate composition. J Inst Brew. 1991;97(2):85–92.