Fermentable Sugar Calculator
Enter ingredient details to calculate fermentable sugar content and estimated ABV.
Understanding Fermentable vs. Non-Fermentable Sugars
Not all sugars ferment. Yeast can only metabolize certain sugar molecules (glucose, fructose, sucrose), while others pass through unchanged (like maltodextrin in grain). For brewers and fermentation hobbyists, understanding which sugars ferment—and how much—is critical for predicting final alcohol content, residual sweetness, and fermentation success. A beer brewer might expect 10% ABV from their recipe, but if they haven't accurately calculated fermentable sugars, they might end up with 8% or 12%. Similarly, a wine maker needs to know the starting gravity (sugar content) to understand when fermentation is complete and estimate shelf stability. This calculator helps you identify the true fermentable sugar content in common brewing and fermentation ingredients, accounting for losses during extraction (mashing efficiency for grains) and inherent non-fermentable components.
Fermentable Sugar Chemistry
The fundamental equation relating sugar content to alcohol potential is:
Original Gravity (OG) is measured in specific gravity units (1.000 for pure water). A one-degree increase in gravity (e.g., from 1.040 to 1.041) represents approximately one gravity point. Each pound of sugar per gallon of water adds approximately 46 gravity points. So if your batch contains 5 lbs of fermentable sugar in 5 gallons, that's 1 lb/gallon × 46 = 46 points per gallon, or 1.046 OG, giving approximately 6% potential ABV. Malt grains are more complex because they contain both fermentable (sugars released during mashing) and non-fermentable (fiber, proteins, β-glucans) components. The typical "points per pound per gallon" (PPG) for two-row barley is about 37, meaning 1 lb of grain in 1 gallon of water yields 1.037 gravity if extracted at 100% efficiency. Real mashing efficiency is typically 60–75%, so 1 lb in 1 gallon at 70% efficiency yields 1.026 gravity.
Worked Example: Brewing with Multiple Ingredients
Suppose you're making a 5-gallon batch with 8 lbs of two-row barley (PPG 37), 1 lb of honey, and 0.5 lbs of table sugar, aiming for 70% mashing efficiency. Barley contribution: 8 lbs × 37 PPG × 0.70 efficiency = 206.8 gravity points. Divided by 5 gallons = 41.4 points from grain. Honey contribution: 1 lb of honey is nearly 100% fermentable, ~46 gravity points × 1 lb = 46 points. Table sugar contribution: 0.5 lbs × 46 points = 23 points. Total gravity points: 41.4 + 46 + 23 = 110.4 points. OG = 1.110. Potential ABV = (1.110 − 1.0) / 0.0075 = 14.7% ABV if all sugars ferment. If your yeast has a lower attenuation (say 70%), the final gravity might be 1.033, giving 10.3% actual ABV and ~15 grams/liter of residual sweetness. This is useful information—you now know whether your beer will be dry or sweet, and whether your yeast can handle the alcohol level.
Fermentability and Attenuation by Ingredient
| Ingredient | Fermentable % | PPG (per lb/gal) | Typical Attenuation | Notes |
|---|---|---|---|---|
| Two-Row Barley | 80–85% (at 70% eff.) | 37 | Variable (60–80%) | Most common brewing grain |
| Wheat Malt | 80–85% (at 70% eff.) | 37 | 70–80% | Higher enzymes, good conversion |
| Honey (Bee Pollen) | 95%+ fermentable | 46 | 90–100% (dry finish) | Nearly 100% fermentable, smooth finish |
| Table Sugar (Sucrose) | 100% fermentable | 46 | 100% | Fast fermentation, neutral flavor |
| Corn Sugar (Dextrose) | 100% fermentable | 46 | 100% | Fast fermentation, neutral |
| Molasses | 75–85% fermentable | 35 | 70–85% | Complex flavors, slower ferment |
| Fruit (Apple, Grape) | 85–95% fermentable | 5–15 (varies) | 80–95% | Depends on ripeness and type |
| Fruit Juice (Fresh) | 90%+ fermentable | Variable | 90–100% | Pre-extracted, clean ferment |
Practical Applications for Brewers and Fermenters
Understanding fermentable content helps you: (1) Predict final alcohol content and adjust recipes to target desired ABV; (2) Select yeast appropriate for the alcohol level (not all yeasts tolerate 15% ABV); (3) Estimate final gravity and residual sweetness; (4) Spot check recipe calculations for reasonableness; (5) Compare ingredient efficiency (honey vs. grain vs. sugar); (6) Adjust batch sizes without recalculating everything from scratch. For instance, if you want to make a 6% ABV beer instead of a 5% ABV beer, you know you need to add roughly 5–6 more gravity points (about 0.2 lbs of grain or 0.1 lbs of honey). For kombucha fermentation (which uses juice, not grain), the calculation is simpler—just know your starting sugar content (typically 8–12% sugars in tea, more in juice) and assume 70–80% fermentation, giving a final product with 1–3% residual sugar depending on attenuation and fermentation duration.
Mashing Efficiency and Grain Losses
Mashing efficiency (the percentage of potential sugars you actually extract from grain) depends on several factors: grain crush (finer = higher extraction), water temperature during mashing (optimal 150–160°F), mash pH (ideal 5.2–5.5), mashing time (typically 60 minutes), and grain condition (old grain extracts poorly). Home brewers typically see 65–75% efficiency; commercial breweries with optimized equipment reach 80–90%. If your recipe assumes 70% efficiency but you only achieve 60%, your beer will be 14% weaker than intended. Conversely, if you achieve 75%, your beer will be 7% stronger. Over time, track your actual efficiency by comparing expected vs. actual gravity and adjust future recipes accordingly.
Yeast Attenuation and Residual Sweetness
Attenuation is the percentage of fermentable sugars the yeast actually converts to alcohol (the remainder stays as residual sugar). A high-attenuation yeast (like American ale yeast at 75–85%) ferments most sugars, leaving a dry beer. A low-attenuation yeast (like some English strains at 60–70%) leaves more residual sweetness. Knowing both your starting gravity and your yeast's typical attenuation lets you predict final gravity: Final Gravity = Original Gravity − ((OG − 1.0) × Attenuation). For example, OG 1.060, 75% attenuation: FG = 1.060 − ((0.060) × 0.75) = 1.060 − 0.045 = 1.015. This is a slightly sweet beer (residual sugars balance alcohol warmth). This knowledge helps you choose yeast for the right character—dry yeasts for dry beers, less attenuative yeasts for sweet ciders or meads.
Limitations and Assumptions
This calculator uses average values for ingredient fermentability and typical mashing efficiency. Real results vary based on grain age, water chemistry, technique, and equipment. Additionally, some ingredients (like fruit) have highly variable sugar content depending on ripeness and variety. Test your results against known batches to calibrate your personal efficiency. Finally, this calculator assumes temperature-stable fermentation and doesn't account for non-biological losses (evaporation, settling of yeast). For precision, measure gravity with a hydrometer at the start and end of fermentation.