Degrees Brix (°Bx) approximates grams of sucrose per 100 grams of solution. Winemakers use pre-fermentation Brix to estimate potential alcohol, often with a factor around 0.55–0.60. It is a planning estimate, not the measured ABV of the finished wine.
What one degree Brix means
The International Organisation of Vine and Wine defines 1° Brix as one gram of sugar per 100 grams of solution in its grape-sugar reference. A refractometer estimates soluble solids from refractive index, typically calibrated to sucrose. In grape must, most soluble solids are sugars, but not all of them are fermentable sugar.
That distinction explains why a 22°Bx must is not literally 22 grams of sugar per 100 milliliters and why multiplying Brix by one exact factor cannot predict every wine. Acids, minerals, and other extract contribute to the reading; yeast uses some sugar for biomass and metabolites; and ethanol can be lost during production.
Potential-alcohol conversion factors
| Starting Brix | At 0.55 | At 0.60 | Planning range |
|---|---|---|---|
| 18°Bx | 9.9% | 10.8% | About 10–11% ABV |
| 20°Bx | 11.0% | 12.0% | About 11–12% ABV |
| 22°Bx | 12.1% | 13.2% | About 12–13% ABV |
| 24°Bx | 13.2% | 14.4% | About 13–14.5% ABV |
| 26°Bx | 14.3% | 15.6% | About 14–15.5% ABV |
Iowa State University Extension publishes a planning table using 0.55. UC Davis Viticulture and Enology recommends about 0.60 for planning a yeast strain that can tolerate the potential ethanol, while noting that even this can slightly overestimate actual production. The difference is not a contradiction: the estimates serve different planning margins.
Use the conservative high estimate when checking whether a yeast strain and fermentation conditions can handle the must. Use laboratory analysis or a validated finished-wine method when the actual ABV matters for labels, taxes, or sale.
Measure Brix before fermentation
Calibrate the instrument
Clean the prism and verify the refractometer with distilled water according to its manual. Automatic temperature compensation has limits; allow the instrument and sample to approach the intended temperature. A scratched, dirty, or sticky prism can blur the boundary line.
Take a representative sample
Mix the must thoroughly without unnecessary aeration. Juice from the top of a poorly mixed tank may differ from dense material at the bottom. Strain out grape solids that keep the prism from closing flat, but do not dilute the sample.
Read and repeat
Place the required drops on the prism, close the cover, wait briefly for temperature equilibration, and read the boundary. Clean and repeat. Two close readings are more trustworthy than one hurried measurement.
Record the context
Write the date, sample temperature, instrument, raw Brix, lot, and any additions already made. “22 Brix” without knowing whether sugar or water was added before the reading is an incomplete production record.
Use Brix to plan sugar additions
For a rough mass-based addition, one degree Brix is one percentage point by solution mass. Raising 10 kilograms of must by two Brix points begins with an estimate near 200 grams of sugar, but adding sugar also increases total mass, so the exact mass-balance equation is:
sugar = must mass × (target fraction − current fraction) ÷ (1 − target fraction)
For 10,000 grams at 20°Bx targeting 22°Bx:
10,000 × (0.22 − 0.20) ÷ (1 − 0.22) = 256.4 g sugar
Our wine sugar calculator uses this mass-balance method and shows both sugar addition and potential-alcohol estimates. It assumes the Brix readings behave like sucrose mass fractions. Real grape must composition and measurement uncertainty mean you should mix fully and remeasure after any addition.
Sugar additions are regulated or prohibited in some wine regions and categories. Check local law before chaptalization. The calculator is arithmetic, not legal authorization.
Do not read raw Brix as sugar after fermentation begins
Ethanol changes refractive index. Once alcohol is present, a refractometer’s raw Brix display no longer directly reports remaining sugar. A fermentation can even show a positive-looking refractometer value after most fermentable sugar is gone.
Post-fermentation correction models require the original reading and make assumptions about wort or must composition. They are useful for tracking but remain estimates. For residual sugar decisions, professional wineries use appropriate analytical methods rather than a raw handheld refractometer.
A hydrometer also needs interpretation during wine fermentation. UC Davis notes that a Brix-style density curve can fall below zero because an ethanol-water mixture is less dense than water. Negative Brix on a hydrometer scale does not mean “negative sugar.”
Potential alcohol is not finished alcohol
Potential alcohol assumes fermentation to dryness with a typical conversion yield. Actual alcohol can be lower when residual sugar remains, yeast stalls, carbon is used for cell growth and other metabolites, or ethanol is lost. Measurement method and temperature also matter.
Select yeast with tolerance above the estimated potential under the planned temperature, nutrient, and pH conditions. UC Davis explains that nonoptimal temperature, low pH, nutrient limitation, and other stressors can reduce effective tolerance. A label claiming “18% tolerance” does not guarantee completion of an 18%-potential must.
Troubleshoot surprising Brix readings
The reading changes across the vessel
The must is not homogeneous or solids are interfering. Mix appropriately and sample from a representative point. Do not average obviously stratified readings and pretend the underlying mixing problem is solved.
Brix rose after adding fruit or concentrate
That is expected if the addition contains soluble solids. Record the amount, mix, and establish a new effective starting measurement. The original pre-addition Brix can no longer predict the whole batch’s alcohol by itself.
Brix stops falling
Confirm the measurement method is appropriate in the presence of alcohol. Then review fermentation temperature, yeast tolerance, nutrients, pH, and sugar composition. UC Davis provides a diagnostic framework for normal, sluggish, and arrested fermentations; adding more yeast without diagnosis may fail.
Hydrometer and refractometer disagree
Before fermentation, check calibration, temperature, scale conversion, and sample solids. During fermentation, the raw refractometer reading requires alcohol correction. A properly used hydrometer and corrected refractometer should move toward a reasonable interpretation, but neither replaces a lab result where precision is required.
Track fermentation and package safely
Record Brix or gravity and temperature on a consistent schedule. A trend is more informative than an isolated number. Stable density does not always mean a healthy completed fermentation; it can also mean a stall. Consider expected dryness, yeast health, sensory condition, and appropriate analytical tests.
Do not seal wine with uncertain fermentable sugar unless the packaging and process are intentionally designed for pressure. Refermentation can break bottles. Stabilization, sterile filtration, and commercial packaging require technical expertise. For products sold to others, use accredited analysis and comply with the rules of the production and sales jurisdiction.
A repeatable Brix worksheet
For each lot, record fruit source, crush date, must mass or volume, sample temperature, instrument, calibration check, two Brix readings, estimated potential-alcohol range, yeast strain, and planned tolerance margin. After any sugar, concentrate, fruit, or water addition, record its mass and take a new well-mixed reading. Never overwrite the original value; the sequence explains how the must changed.
During fermentation, keep raw refractometer readings clearly labeled so they are not mistaken for corrected residual sugar. If using a correction model, record its name and the original Brix it requires. At completion, record the analytical method used for actual ABV or residual sugar. This small discipline prevents a planning estimate from quietly becoming an unsupported label claim.