Free Wine Must Brix & Gravity Calculator
Convert hydrometer Specific Gravity to °Brix, calculate potential alcohol (ABV %), chaptalization sugar dosing, and water dilution.
🍇 Must Measurements & Target
📊 Potential ABV & Adjustment Dosing
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Understanding Must Gravity, Brix, and Potential Alcohol
In winemaking, measuring the density of fresh grape must before yeast inoculation reveals the concentration of soluble sugars (glucose and fructose). Because sugar is converted by yeast into ethanol and carbon dioxide according to Gay-Lussac's equation, starting sugar dictates the final alcohol by volume (ABV) of your wine.
1. Specific Gravity to °Brix Conversion
Degrees Brix represents the percentage of sucrose by weight in solution (1 °Brix = 1 gram of sugar per 100 grams of must). The conversion between hydrometer Specific Gravity ($SG$) and °Brix is accurately modeled by the polynomial:
2. Potential Alcohol Calculation
Commercial wine yeasts typically convert sugar into alcohol at an efficiency factor of 0.55 to 0.60:
For example, a grape must harvested at 23.5 °Brix will ferment dry to approximately $23.5 imes 0.57 = 13.4%$ ABV.
3. Chaptalization (Sugar Addition) Formula
If cool harvest weather leaves grapes under-ripe with insufficient natural sugar to reach a stable preservative alcohol level (typically 12.5% to 14.0%), table sugar (sucrose) may be added:
Frequently Asked Questions
What is the difference between a hydrometer and a refractometer for wine?
A hydrometer measures physical liquid density via floating displacement and is accurate before, during, and after fermentation. A refractometer measures light refraction; it is fast and accurate on unfermented must, but once alcohol is produced, alcohol distorts light refraction, requiring complex mathematical correction formulas.
Can I use brown sugar or honey instead of white table sugar for chaptalization?
In traditional winemaking, pure white granulated sucrose is preferred because it is 99.9% neutral fermentable sugar that adds alcohol without altering the grape cultivar's delicate fruit aromatics. Brown sugar adds molasses flavors; honey (which is 18% water) changes the wine into a pyment.
Why does finished dry wine read below 1.000 Specific Gravity on a hydrometer?
Pure ethanol has a specific gravity of 0.789, which is significantly lighter than pure water (1.000). When all heavy sugars have been consumed by yeast, a completely dry wine naturally measures between 0.990 and 0.994 SG.
What should I do if my grape must is too high in sugar (e.g. 27 Brix)?
Excessively high Brix can lead to stuck fermentations (osmotic pressure stresses yeast) and hot, unbalanced wine over 15.5% ABV. Winemakers "water back" the must by adding clean, chlorine-free water with 5-6 g/L tartaric acid dissolved in it to lower Brix while maintaining healthy acidity.