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Turbo yeast, wine making kit or beer: |
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Start 1075 (+75). |
Current 998 (-2). |
At the start of your fermentation you will have a mix of: Water (added by you and/or by the wine/beer kit manufacturer) Sugar (added by you or by the wine/beer kit manufacurer) Solids (from grapes or malt etc). At the end of the fermentation, we can say that approximately the only thing that has happened is that some water and most of the sugar has been transformed into alchol and carbon dioxide (the gas that bubbles out through your airlock). The solids, i.e. grapes / malt etc will be mainly unaffected weightwise and volumewise which is the only thing we are considered about when determining alcohol. |
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So if you check the start weight of, say one litre, and the final weight of the same volume - it should be possible to determine how much sugar has been replaced by alcohol. There should then be a formula for the alcohol content with the start and final gravities as variables. Indeed there is - if you use your old school chemistry and calculate the transformation from sugar + water into alcohol + CO2, you will end up with the following formula: Alcohol (by volume) % = ((Start s.g.) - (final s.g.))/8 Or, in plain English: For every 8 s.g. of fermentation, you will get 1% of alcohol. In real life though, it turns out that 2+2 is not 4. During the process, there will be volume contraction and other not so easy-to-explain things going on. It turns out if you actually measure alcohol by more advanced methods that the 8 should be more like 7.3 - 7.7. The value will depend on the start gravity and other things. We have determined 7.4 to be a good value for home beer and wine. |
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