FermCalc - Hydrometer Temperature Corrections and Alcohol Content Calculations
Introduction
The Alcohol Content panel has four functions:
- Correcting your hydrometer readings for temperature.
- Calculating the approximate alcohol content using the specific gravity (SG) drop method.
- Calculating the approximate alcohol and residual sugar contents using the hydrometer & refractometer method.
- Calculating the approximate alcohol content using the boiling off method.
To calculate the alcohol content using the SG drop method, you need to know the initial and final hydrometer SG readings. These calculations are only valid if you have not added any additional water or sugar between the initial and final readings. To calculate the alcohol content using the hydrometer & refractometer method, you need simultaneous hydrometer and refractometer readings. To calculate the alcohol content using the boiling off method, you need two hydrometer readings obtained by the procedure described below. FermCalc can make temperature corrections to the hydrometer readings for all three methods.
Making a Calculation
To make a calculation, follow these steps:
- Select Calculation > Alcohol Content from the menu, or select the Alcohol tab at the top of the main window.
- Select the type of calculation by selecting either the SG Drop Method tab, the Hydrometer & Refractometer Method tab, or the Boiling Off Method tab.
- Select the appropriate units for the input fields using the drop-down menus in the right-hand column.
- If the SG Drop Method was selected, enter the initial and final Hydrometer SG Readings of the wine.
- If the Hydrometer & Refractometer Method was selected, enter the Refractometer Reading of the wine in Brix and the Hydrometer SG Reading of the wine.
- If the Boiling Off Method was selected, enter the initial and final Hydrometer SG Readings of the wine. See the procedure below for instructions on obtaining the initial and final SG readings.
- Enter the Reading Temperature at which the hydrometer SG readings were taken. (If you don't know what these are or if you don't want to do a temperature correction, just leave them set equal to the hydrometer calibration temperature.)
- Enter the Calibration Temperature of the hydrometer(s) used to measure each of the specific gravities.
The temperature-corrected specific gravities and the approximate alcohol content of your wine will appear in the output fields as you type.
All gravity values are converted to specific gravity when they are entered, and are subjected to an upper limit of 1.5805 (pure sugar) and a lower limit of 0.95. Temperatures must range between 0 and 55 C. If any of the entered values are outside of these ranges, output fields are highlighted in red and an error message is displayed.
Calculation details are provided below.
- Hydrometer Temperature Corrections
- Alcohol Content by Gravity Drop Method
- Alcohol Content by Hydrometer & Refractometer Method
- Alcohol Content by Boiling Off Method
Calculation Details - Hydrometer Temperature Corrections
FermCalc allows hydrometer readings to be corrected for temperature in all three of the alcohol content calculation methods. According to tables published in the USDA Technical Inspection Procedures, temperature corrections to Brix measurements are functions of both the temperature and the degrees Brix of the must. Based on these tables, I developed the following equations to correct hydrometer readings.
B = Ba + [a(T - 20)2 + b(T - 20)] - [a(Tc - 20)2 + b(Tc - 20)] (1)
where:
B = corrected Brix
Ba = apparent Brix at temperature T
T = must temperature, °C
Tc = hydrometer calibration temperature, °C
a = 1.4525·10-7Ba2 - 2.5256·10-5Ba + 1.2495·10-3
b = -6.7681·10-6Ba2 + 9.5741·10-4Ba + 4.4857·10-2
The plot below compares the USDA data with the calculated Brix corrections from equation (1) above.
Calculation Details - Alcohol Content by Specific Gravity (SG) Drop Method
Alcohol content is calculated in FermCalc using a standard SG drop method as well as methods proposed by Duncan & Acton and by Balling. All three of these methods require hydrometer measurements of the initial and final specific gravities. (These methods do not work with refractometer measurements.) Agreement between the methods is generally excellent.
Standard SG Drop Method
This method estimates the alcohol content by dividing the drop in gravity by the constant 0.00736, or:
av = (sgi - sgf) / 0.00736 (2)
where
av = alcohol content, % by volume
sgi = initial specific gravity
sgf = final specific gravity
Duncan & Acton Method
The Duncan & Acton method calculates the alcohol content from the initial and final specific gravities divided by a factor F that is a function of the corrected initial specific gravity. The equations are as follows.
av = 1000(sgi - sgf) / F (3) F = 7.75 - 3000(sgc - 1.0) / 800 (4) sgc = sgi - 0.007 (5)
where
av = alcohol content, % by volume
sgi = initial specific gravity
sgf = final specific gravity
F = conversion factor
sgc = initial specific gravity corrected for non-sugar solutes
Combining equations (3) through (5) above yields the following equation:
av = 1000(sgi - sgf) / [7.75 - 3.75(sgi - 1.007)] (6)
Balling Method
The Balling method is normally used for beer but gives results that agree very well with the other methods. The equations used in FermCalc were taken from Michael Hall's article "Brew by the Numbers" in the Summer 1995 issue of Zymurgy magazine. The method requires the calculation of a parameter called "Real Extract", which is an estimate of the residual sugar content after fermentation has finished, as follows:
q = 0.022 + 0.001Bi (7)
RE = (q·Bi + Bf) / (1 + q) (8)
where
q = attenuation coefficient
RE = real extract
Bi = initial Brix
Bf = final Brix
The alcohol content (% by weight) is then calculated as:
aw = (Bi - RE) / (2.0665 - 0.010665Bi) (9)
where aw is the alcohol content in % by weight.
The result of equation (9) is then converted to % alcohol by volume as described here.
Back to topCalculation Details - Alcohol Content by Hydrometer & Refractometer Method
The method used by FermCalc to calculate alcohol content from hydrometer and refractometer readings is described by Rogerson & Symington (2006). The method was developed using laboratory measurements on 35 port wines, and in the words of the authors, "It is not applicable for the analysis of dry wines, whether fortified or not, which contain insufficient soluble solids for Baumé determination by hydrometer, and is yet to be evaluated for sweet table wines, such as sauternes." However it is included in FermCalc because many home winemakers seem to find it useful for monitoring fermentation progress and calculating alcohol content.
FermCalc first converts the hydrometer reading sg to degrees Baumé using the following equation.
Bé = 145 - 145/sg (10)
where Bé is degrees Baumé.
Alcohol content is then calculated as:
av = 1.646Ba - 2.703Bé - 1.794 (11)
where
av = alcohol content, % by volume
Ba = refractometer Brix reading (apparent Brix)
True Brix, Bt, which represents the estimated residual sugar content in % by weight, is then calculated as:
Bt = Ba - 0.358av (12)
An alternative method of performing this calculation is frequently referenced in online winemaking forums. While the origins of the equations used in this alternative method are not clear, my testing indicates that it yields nearly identical results.
Back to topCalculation Details - Alcohol Content by Boiling Off Method
This method is described on pages 124-126 of "The Art of Making Wine" by Stanley F. Anderson and Raymond Hull, and is attributed to the researches of Dr. William Honneyman. (I've been trying to get a copy of Dr. Honneyman's original report but so far I've been unsuccessful.) The procedure is summarized below.
- Measure the specific gravity (sgi) of the wine you wish to test.
- Take a sample of about one pint of the wine and boil the sample down to approximately half of its original volume.
- Add distilled water to the sample until the total volume is the same as the original sample volume.
- Allow the mixture to cool to room temperature and measure the new specific gravity (sgf), which should be greater than sgi because the alcohol has been replaced by water.
- Take the difference between the new specific gravity (sgf) and the original specific gravity (sgi) and look up the alcohol content in the table below.
If the difference (sgf - sgi) is greater than the maximum value in the table, FermCalc extrapolates the table and displays a message to that effect.
| sgf - sgi | Alcohol Content (% by volume) |
| 0.0000 | 0.0 |
| 0.0015 | 1.0 |
| 0.0020 | 1.3 |
| 0.0030 | 2.0 |
| 0.0040 | 2.7 |
| 0.0050 | 3.4 |
| 0.0060 | 4.1 |
| 0.0070 | 4.9 |
| 0.0080 | 5.6 |
| 0.0090 | 6.4 |
| 0.0100 | 7.2 |
| 0.0110 | 8.0 |
| 0.0120 | 8.8 |
| 0.0130 | 9.7 |
| 0.0140 | 10.5 |
| 0.0150 | 11.4 |
| 0.0160 | 12.3 |
| 0.0170 | 13.2 |
| 0.0180 | 14.1 |
| 0.0190 | 15.1 |
| 0.0200 | 16.0 |
| 0.0210 | 17.0 |
| 0.0220 | 18.0 |
| 0.0230 | 19.0 |
| 0.0240 | 20.0 |
| 0.0250 | 21.0 |
| 0.0260 | 22.0 |
In addition to the alcohol content, we can also estimate the solids content (True Brix) since we have a specific gravity measurement on a sample with all of the alcohol driven off. FermCalc calculates the solids content by converting the final specific gravity measurement to a Brix value as described on the Conversions page.
© 2007-2010 Steve Gross
Last updated
11 May 2010.