fraction). Subtract the volume of base wine fromthe final volume, to calculate the volume of high proof alcohol required. Check out the accompanying
illustration. If you search for “Pearson Square” on the Internet, there are lots of sites that have calculators. A confusing, recurring problemis the
difference between percent byweight and percent by volume.Wine is a mixture of alcohol andwater,with various things suspended in it. If all the constituents had the same density as water, then percent byweight and percent by volumewould be the same. With alcohol-volumemixtures, the conversion isn’t
linear.Use a table. One quick illustration of this is if
cane sugar is added to adjust the sweetness prior to bottling.When you add cane sugar, a kilo of sugar increases the volume by about 620mL. This also lowers the percentage of alcohol. For instance, in the previous
example, if youwere producing a sweet, high-alcohol dessertwine and you already had 20 percent alcohol by volume,whatwould your final alcohol be if you sweetened it to 60 g/L of
residual sugar? This is a little trickier than itmight seem. Express the residual sugar as percent sugar by volume, rather than byweight. Thus, the desired sugarwill be 3.72 percent (6 X 0.62) by volume instead of 6.0. For the 1370 litres of 20 percent
alcoholwine in the previous calculation, sugar = 1370 + ( (1+ (1370 X 0.0372)) = 1421 litres final volume. The alcohol contentwill be 20 X (1370/1421) = 19.28. The amount of sugar required = (1421 – 1370 )/0.620 = 82.26 kilos. There is a slight error here, probably because the sugar
volume is not exact. To test if thewine is icrobiologically
stable, use theDelle Equation:Delle Units = A + 4.5 C,where A = percent residual sugar and C= percent alcohol by volume. TheDUrequired for stability is
approximately 80, but in practice, the pHalso plays a role andmanywines are stable atDUs in the range of 76 to 78. The abovewinewould have: A = 5.9, C= 19.28 to produce 92.66
DUs. No problem. —Gary Strachan is posted on
LinkedIn.
28
British Columbia FRUIT GROWER • Summer 2013
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