Grain Bill Calculator

PPG — Points Per Pound Per Gallon. Every grain has a theoretical maximum extract value expressed as PPG: the number of gravity points contributed by one pound of that grain dissolved into one US gallon of water, at 100% efficiency. Corn has a PPG of 32, malted barley 37, table sugar 46. The calculator uses these values as the basis for all OG estimates.

Expected gravity units (GU). For each grain in your bill: GU = weight (lb) × PPG × (efficiency ÷ 100). The GU contributions from all grains are summed and divided by your mash volume in US gallons to give total GU per gallon. OG is then: OG = 1.000 + (total GU ÷ 1000). For example, 5 lb of malted barley at 70% efficiency into 1.5 gallons contributes 5 × 37 × 0.70 = 129.5 GU, giving a pre-division total that then becomes an OG reading once divided by volume.

Potential ABV. Assuming full fermentation to 1.000 FG: ABV ≈ (OG − 1.000) × 131.25. This is the standard Balling approximation. Actual fermentation ABV will be slightly lower if FG finishes above 1.000, which is typical for grain mashes (1.008–1.015 is normal for a beer-style mash).

Water-to-grain ratio (W:G). Simply total water volume ÷ total grain weight. Expressed in L/kg (metric) or qt/lb (imperial). A ratio of 3–4 L/kg is standard for a traditional mash tun. Thinner mashes improve enzyme efficiency and are easier to work with; thicker mashes conserve heat better and are typical in traditional pot still distilling.

Strike water temperature. Uses the Palmer formula: T_strike = (0.41 ÷ R) × (T_mash − T_grain) + T_mash where R is the water-to-grain ratio in L/kg and temperatures are in °C. The constant 0.41 is the specific heat ratio of grain relative to water. The formula calculates how hot your water must be so that when mixed with room-temperature grain (assumed 20°C) it lands at your target mash temperature. A thicker mash (lower R) requires hotter strike water because less water is carrying more heat into more grain.

Grain absorption. Grain absorbs approximately 0.65 L per kg of total grain weight during mashing. This volume never makes it to the fermenter. Post-mash volume = water added − grain absorption. On a 5 kg grain bill, roughly 3.25 L stays in the grain and is lost unless you sparge.

Water-to-grain ratio (W:G) affects both mash efficiency and fermentability. A ratio of 3–4 L/kg (1.4–2 qt/lb) is typical for a traditional mash tun. Thinner mashes (higher W:G) are easier to work with and generally give better efficiency but produce a more dilute wort. BIAB (Brew in a Bag) often runs at 5–7 L/kg.

Mash efficiency is how much of the available starch extract in your grain you actually converted and collected. For home distillers using a simple mash tun or pot, 65–72% is realistic. Better crushing, longer mash times, and correct temperature improve efficiency. Commercial distilleries typically achieve 80–90%.

Enzymes and conversion. Unmalted adjuncts — cracked corn, flaked rye, flaked wheat — cannot self-convert. They contain the starches but lack the amylase enzymes needed to break them down into fermentable sugars. You have two options: include at least 15–20% malted barley (which is enzyme-rich) in the grain bill to convert the adjuncts, or add commercial exogenous amylase enzymes directly to the mash.

Strike water temperature. Adding hot water to room-temperature grain drops the temperature. Strike water is always hotter than your target mash temperature to account for this heat loss. The amount of temperature drop depends on your water-to-grain ratio — the thinner the mash, the smaller the drop.