About º Brix, Glucose + Fructose, and Potential Alcohol
The amount of fermentable sugar (glucose + fructose) in juice and the average conversion rate of sugar into alcohol can be used to predict the potential alcohol level in wines.
Choosing Glucose + Fructose instead of º Brix for Alcohol Predictions:
While ºBrix can provide a quick estimate of sugar content, it is not an accurate representation of the fermentable sugars, but rather a measure of all dissolved matter in the must. Using ºBrix can give you an inaccurate measure of fermentable sugar and may add an additional layer of uncertainty to alcohol predictions. Differences between ºBrix and actual fermentable sugar content are even more pronounced in high ºBrix fruit and in fruit affected by fungal growth.
Glucose + Fructose analysis, on the other hand, provides accurate information on the levels of fermentable sugar. Glucose + Fructose numbers often appear higher than the corresponding ºBrix results in ripe fruit. The reason for this is that ºBrix is measured as a percentage by weight measurements, meaning ºBrix values are greatly
influenced by the density of the juice. Glucose + fructose is measured as weight by volume and is independent of juice density.
Estimating Potential Alcohol:
|ESTIMATED CONVERSION RANGES
||ETHANOL (% Vol)
||10.0 - 10.9
||10.6 - 11.5
||11.1 - 12.1
||11.7 - 12.7
||12.2 - 13.3
||12.8 - 13.9
||13.3 - 14.5
||13.9 - 15.2
||14.4 - 15.8
The conversion rate used is:
Potential Alcohol (% vol) = glucose + fructose (g/L) / 16.83
It is important to remember that the actual conversion rates vary with yeast properties and fermentation conditions and the potential alcohol is only an approximation. Alcohol conversion ratios are always subject to variability during fermentation, so it’s possible
your actual alcohol may be lower or higher than the estimate. Regardless, this calculation provides a good starting point for estimating potential alcohol.
Many clients have found that the conversion rates observed for their own yeasts and fermentation conditions generally remain relatively constant and use their internally observed rates to calculate potential alcohol content based on their glucose + fructose values.
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