Pot Still Distillation & Fraction Cuts Calculator
Model pot still alcohol mass balance, foreshots discard, heads, hearts, and tails volumetric cuts, spirit proof, and boiler thermal run times.
Boiler Charge & Wash Chemistry
Distillate Cut Points
Distillate Fraction Yields
Boiler Run Logistics & Residuals
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Engineering Fundamentals: Pot Still Distillation & Fraction Cuts
Batch distillation in a traditional copper pot still separates volatile compounds based on boiling points and liquid-vapor equilibrium (VLE). Distillers partition the distillate stream into four distinct operational fractions.
1. Distillation Cut Definitions
- Foreshots: The initial condensate containing poisonous methanol, acetone, and ethyl acetate. Always discarded (rule of thumb: 150–250 mL per 100 liters of wash).
- Heads: Early run containing pungent aldehydes and light esters. Collected separately and recycled into the next stripping charge ("feints").
- Hearts: The clean, potable center cut rich in ethanol and desirable congeners (higher alcohols, lactones, oak precursors). Collected between roughly 140 and 105 proof.
- Tails: Late run dominated by bitter fusel oils, propanol, and water. Collected down to 20 proof and recycled into the feints receiver.
2. Thermal Boil-Up Energy
Heating a wash from room temperature to boiling requires sensible heat (Q = m × Cp × ΔT), while vaporizing the ethanol-water mixture requires latent heat (~850 kJ/kg for 50/50 mix). Still run duration depends on net heat transfer rate from steam jackets or electric immersion elements.
Frequently Asked Questions
Why must foreshots be strictly separated and discarded in distillation?
Foreshots are the lowest-boiling fractions that emerge first from the condenser. They contain concentrated methanol (boiling point 64.7°C), acetone, and noxious volatile organic compounds that cause blinding, severe headaches, and unpleasant chemical aromas.
What is the difference between heads, hearts, and tails?
Heads contain fruit esters and spicy aldehydes that can add complexity in small amounts but cause harsh hangovers if excessive. Hearts contain pure ethanol and pleasant sweet esters. Tails contain heavy fusel alcohols and fatty acids that taste wet-cardboard-like at high concentrations.
What are "feints" in commercial whiskey distilleries?
Feints are the combined heads and tails fractions saved from previous spirit runs. Rather than being dumped, feints are pumped into the feints receiver and added to subsequent low wines charges, recovering trapped ethanol without spoiling the heart cut.
What is spent wash (pot ale / backset)?
Spent wash (pot ale in Scotland, backset in Kentucky) is the acidic, non-volatile liquid remaining in the still after all alcohol has boiled off. In bourbon production, 20% to 35% of backset is added back into the next mash cooker ("sour mash") to lower pH and suppress bacterial infection.