What temperature should I see when distilling at 50% ABV?

At sea level (101.325 kPa), an ethanol-water vapour produces 50% ABV distillate at approximately 83.8°C vapour temperature. Thermometer placement in the lyne arm will match most closely.

Why does altitude affect distillation temperature?

At higher altitudes, atmospheric pressure is lower, which reduces the boiling point of ethanol-water mixtures. At 1000 m elevation, distillation temperatures are about 3–4°C lower than at sea level.

Can I use still temperature to time my cuts?

Temperature gives a useful guide but should not be your sole method when using a pot still. The ethanol-water VLE curve flattens significantly between 40–80% ABV — a 5°C change can represent a 15–20% ABV swing.

Where should I place my thermometer in a pot still?

For vapour temperature readings, place the probe in the vapour path — in the swan neck or lyne arm just above the pot. Thermometers in the pot liquid measure liquid temperature and will give incorrect ABV estimates.

Alcohol Vapour Temperature versus AbV

Harris Organic Distillery

Convert your still thermometer reading to distillate ABV

Here is an Alcohol Vapour Temperature versus AbV tool I use to calculate the percentage of my moonshine or brandies to find the exact percentage of alcohol left in my still. You can use it too!
Convert your still thermometer reading to distillate ABV — or find the expected temperature for a target ABV.
Corrects for altitude and atmospheric pressure automatically.

Pot Still - Vapour Temperature ↔ ABV Calculator

Vapour Temperature

°C

Valid range: 78.15°C – 100°C at sea level

Distillate ABV

Valid range: 0% – 96.2% ABV

Atmospheric Pressure

hPa

Standard sea level = 1013.25 hPa

Or enter altitude

Converts to pressure

Vapour Temp Output

—°C

Calculated ABV

—%

UK Proof

—

US Proof

—

Shift Error

—°C

Understanding the Vapour Liquid Equilibrium (VLE) Curve

The relationship between vapour temperature and distillate ABV comes from the vapour-liquid equilibrium (VLE) of ethanol-water mixtures. At any given temperature, ethanol and water are present in the vapour above the boiling liquid in a proportion determined by their relative volatilities and the non-ideal molecular interactions.

Ethanol is more volatile than water — it prefers to stay in the vapour phase. This is why a pot still enriches ethanol: the vapour that rises is always richer in alcohol than the liquid boiling below it. As distillation proceeds, the ethanol in the boiler is depleted, the liquid gets more watery, and the vapour temperature rises. This is exactly what your still thermometer tracking measures over a run.

The curve is not linear — the ABV drops slowly at first when temperatures are near the azeotrope (78.15°C / 97.2% ABV), then drops increasingly steeply as the run progresses toward pure water at 100°C.

Why Atmospheric Pressure Matters

Water boils at 100°C at standard sea-level pressure, but at lower temperatures at altitude because atmospheric pressure drops and the pressure in your still drops. The same applies to ethanol-water mixtures, the entire tracking curve shifts downward as altitude increases.

Pressure correction offset ≈ (1013.25 − P) × 0.037 °C/hPa

If you use a static sea-level table at altitude, every thermometer reading will be off by 2–4°C — which translates to a significant 5–15% ABV calculation error. This calculator handles that offset step dynamically.

Spirit Temperature Correction

If you want to know how much alcohol percentage is in your collection jar at room temperature conditions, look up our dedicated Spirit Temperature Correction Calculator to adjust the direct hydrometer measurement readings.

Try this out here: Spirit Temperature Correction Calculator

Sea-Level VLE Calibration Reference Table

Vapour Temp (°C)	Vapour Temp (°F)	Distillate ABV	US Proof

Harris Organic Spirits