A still has three working parts: a vessel that boils the liquid, a vapour path that carries the vapour away, and a condenser that turns it back to liquid, and the condenser is the part that is most often undersized. Condensing one kilogram of ethanol vapour releases about 840 kJ, which takes roughly 10 litres of cooling water warming by 20 °C, and the whole apparatus must stay open to the air so that heating never builds pressure. Build it from materials that tolerate hot vapour and contain no lead.
Part of Organic Chemistry
The vessels, vapour paths and condensers that separate liquids by boiling point, built from copper, steel, glass or ceramic.
Boiling Point Is The Only Separator; Everything Else Is Plumbing
Distillation works because different liquids boil at different temperatures. The carrier uses it two ways: steam distillation, where steam carries volatile plant compounds out of the material, and spirit distillation, where a fermented wash is heated and the alcohol-rich vapour is collected. The detail of building a pot still, a lyne arm and a coil condenser is in Still Construction and Condenser Coil; this article states the principles the build must satisfy.
What You Need
- A boiler of copper, stainless steel or heavy ceramic with a sealed-but-vented lid. Iron pots can be used for a wash, but acid or sour ferments corrode them.
- A vapour path, called a lyne arm, that rises or slopes continuously toward the condenser so condensate cannot dam in it.
- A condenser: a coil in a water jacket or tank, or a tube-in-tube. See Heat Exchangers for the counterflow rule.
- A receiver, glass or glazed, with the condenser outlet positioned so you can see the drip.
- A thermometer in the vapour, not in the liquid, because the vapour temperature identifies what is coming over.
- Seals of flour paste, cork or lead-free solder. Do not use lead solder or lead-bearing alloys anywhere the vapour or condensate touches, because lead dissolves into acidic condensate.
Method: Setting Up And Running A Still Safely
Step 1: Assemble the whole path and test it cold with water. Every joint must be tight enough to hold vapour but one point must remain open to the air.
Step 2: Run cooling water counterflow: cold in at the lowest point of the condenser, warm out at the top. The distillate leaving the condenser should be cool to the touch. If it is hot, the condenser is too small or the water too slow.
Step 3: Heat gently and steadily. Dripping, not running, is correct. A thin continuous stream means the heat is too high and the vapour is carrying through the condenser uncondensed.
Step 4: Stay with it. A still is never left unattended; a fire, a blocked arm or loss of cooling water becomes an emergency in minutes.
Cuts Are About Flavour, Not Poison
Collect the run in small jars so you can separate fractions by smell and vapour temperature. The first jars smell sharp because of acetaldehyde and ethyl acetate; they are discarded for taste. Do not treat the discard as removing methanol: published measurement finds methanol spread through almost all fractions, and what controls the methanol in a spirit is the feedstock. Fruit and pomace carry far more than grain or sugar washes, and no volumetric rule makes a distillate safe to drink. The authoritative treatment, with the sources and arithmetic, is Methanol Hazards; the fraction handling is in Heads, Hearts, Tails.
Worked Example: Sizing The Condenser Water
Assume the still delivers 1 kg of ethanol vapour per hour to the condenser.
- Heat to remove: 1 kg × about 840 kJ/kg = 840 kJ per hour. The figure is the latent heat of vaporisation of ethanol, taken from general reference values, not from the corpus.
- Allow the cooling water to warm by 20 °C. Water absorbs about 4.18 kJ per kg per °C.
- Water needed: 840 ÷ (4.18 × 20) = 840 ÷ 83.6 ≈ 10 kg, or about 10 litres per hour.
That ignores sub-cooling the liquid after it condenses, so treat 10 litres as the floor, and allow more for a warm water supply. A condenser fed by a trickle gets hot and passes vapour.
How much vapour a leak makes. One kilogram of ethanol is 1,000 ÷ 46 ≈ 21.7 mol. At room temperature one mole of gas occupies about 24 L, so 21.7 × 24 ≈ 520 L of vapour. The lower flammable limit of ethanol in air is quoted as 3.3% on Fire Safety, so 520 ÷ 0.033 ≈ 15,800 L, about 16 m³ of air brought to the flammable limit by one kilogram. A leak in a small shed gets there quickly.
Common Mistakes
- Sealing the system closed. Heating a closed vessel builds pressure until a joint fails. Keep a vent on the receiver end.
- Undersizing the condenser. Uncondensed vapour leaves as a flammable plume.
- Using galvanised or lead-bearing materials, which put zinc or lead into the product.
- Treating the foreshots discard as a safety step. It is a flavour step.
Safety
Ethanol vapour is invisible, heavier than the air it displaces, and ignites at a low concentration
Run the still outdoors or in an open-sided shelter, with no flame, hot plate or spark within several metres of the vapour path. Do not test for vapour with a lit match, candle or lighter; detect leaks by smell and by watching joints for beading. Keep the heat source away from the receiver, keep a bucket of water and sand at hand, and never refill a hot boiler. Methanol is the reason a distillate from any wash must not be given as a drink: see Methanol Hazards.
What’s Next
- Learn next: Bioethanol — distilling to fuel strength
- Combine with: Solvent Extraction — recovering solvent by distillation