Understanding Wine Chemistry by Andrew L. Waterhouse & Gavin L. Sacks & David W. Jeffery

Author:Andrew L. Waterhouse & Gavin L. Sacks & David W. Jeffery
Language: eng
Format: epub
ISBN: 9781118730706
Publisher: Wiley
Published: 2016-09-13T00:00:00+00:00

Notes

1 This “aerobic fermentation” behavior, also referred to as the Crabtree effect, may have evolved in yeast as a way to provide a competitive advantage over other microorganisms due to the antiseptic properties of ethanol. Based on genetic analyses, it is reported that the trait likely evolved at the end of the Cretaceous Age around the same time as fleshy fruits [2].

2 Predicting ethanol yield prior to fermentation in wineries is further complicated because typical sugar measurements on grapes are measured as “soluble solids,” in units of Brix (g of sugar per 100 g of juice). These values are based on physical measurements like density and will usually over-report sugar concentrations by 5–10% due to the presence of other solutes like acids and minerals. Small amounts of ethanol (equivalent to 0.1–0.2% v/v) may also be lost as vapor due to CO2 entrainment. A final complication is that sugar concentrations may be underestimated in shriveled grapes due to higher concentrations of sugar in the skins.

3 In industrial microbiology settings, adding bisulfite to fermentations to induce glycerol formation has been used since 1915, where the glycerol was utilized in production of nitroglycerin explosives.

4 In media with low endogenous acid concentrations, such as in sake production, succinic and other organic acids will represent the major contributors to titratable acidity.

5 Note that this is the third time in this chapter that the reducing environment of fermentation has been mentioned – this is an important concept.

6 As a reminder PV = nRT; solved for V (in litres) given that P = 1 atm, n ≈ 2.22 moles, R = 0.08206 L atm mol-1 K-1 and T = 298.15 K (i.e., 25 °C).

7 The combination of heat and CO2 generation explains the Latin root of fermentation (fervere, “to boil”), a mystical phenomenon until Louis Pasteur’s identification of yeast as the responsible party in the 1860s.

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