The Potential Alcohol Calculator estimates the alcohol content of a wine that will result from the complete fermentation of a must with a given initial specific gravity. Nine methods are used to estimate the potential alcohol content:
Most of these methods assume some sugar to alcohol conversion factor less than the theoretical maximum of 0.511 grams of alcohol per gram of sugar. Most of them also make an allowance for the presence of non-fermentable solids, most commonly assumed to be 30 g/L. The actual alcohol content will depend on the composition of the must and on the efficiency and completeness of the fermentation, so it is best measured after fermentation is finished.
Because of the approximate nature of these calculations, no temperature corrections are made to the SG or to the calculated alcohol contents. The SG measurement should be made near 20°C (68°F). For all of the methods below, conversions between SG and Brix are made using the SG to Brix conversion equation, which has a temperature basis of 20°C (68°F).
Input Field Definitions
Initial Must SG – The SG (20°C/20°C) of the must prior to the start of fermentation. Range: 1.0 to 1.5545 (0° to 100° Brix).
Fermentation Factor – This is the factor multiplied by Brix in the User Defined method. A range is not enforced, but this is usually in the range between 0.55 and 0.63.
Output Field Definitions
Potential Alcohol Content – The estimated alcohol content after complete fermentation.
The calculations involved in the nine potential alcohol calculation methods are described in detail below.
This method is reported by Boulton et al (1999) and is attributed to Dubrunfaut.
ap = 0.059(2.66·Oe – 30)
ap = potential alcohol content, % by weight
Oe = 1000(sgi – 1)
sgi = initial specific gravity of the must
George Marsh (1958) proposed using a fermentation factor of 0.47 grams of alcohol per gram of sugar. The sugar content is calculated from the measured Brix minus a correction factor of 30 g/L (3 g/100 mL). The result is then divided by the density of alcohol to yield alcohol content in percent by volume. This yields the formula:
ap = 0.47(Bisgiρw – 3)/ρa
Bi = Brix value corresponding to sgi
ρw = density of water = 0.9982 g/mL at 20°C
ρa = density of alcohol = 0.7892 g/mL at 20°C
Margalit (2004) calculated that 1.75°Brix results in 1% alcohol by volume, resulting in the formula:
ap = 0.57Bi
Cooke & Lapsley Method
Cooke & Lapsley (1988) proposed a formula very similar to that of Marsh (1958), the main difference being that it uses a corrected SG corresponding to the corrected Brix:
ap = 0.59Bcsgc
Bc = corrected Brix = (Bi – 3)
sgc = SG corresponding to Bc
The official table for determining potential alcohol from Brix in the EU can be found in Table II (page 17) of The Official Journal of the European Communities (CEC, 1990). FermCalc interpolates values of potential alcohol from this table using the Brix value corresponding to the initial must SG.
Daniel Pambianchi (2008) proposed the following formula to calculate a theoretical potential alcohol content:
ap = 0.55Bi – 0.63
Duncan & Acton Method
This method uses the Duncan & Acton SG drop equation assuming that the final SG (sgf) is 1.0:
ap = 1000(sgi – 1.0)/[7.75 – 3.75(sgi – 1.007)]
William Honneyman (1966) developed the following equation for potential alcohol of musts prepared with cane sugar:
ap = 165.9sgi – 168.2
User Defined Method
In this method, the user supplies a factor f to be multiplied by the initial Brix of the must:
ap = f·Bi