IFoundations
From ferment to still
Sugar, ferment, distil, finish. Pot and column stills, and what happens after.
6 min read
Every spirit starts as something sugary and wet. Yeast eats the sugar and gives off alcohol and carbon dioxide, which gets you to roughly 8% - beer or wine, depending on what you started with. Distillation then concentrates that. It doesn't create alcohol; it separates what's already there.
- Raw material. Grain, grape, cane, agave, potato, apple. If it has sugar in it, or starch that can be turned into sugar, it can be fermented.
- Convert, if you have to. Grain and agave hold their sugar as starch or inulin, which yeast can't eat. Malting a barley, or roasting an agave, breaks that down into something yeast can consume.
- Ferment. Add yeast, wait. You get to around 8% alcohol, because the yeast is eventually poisoned by what it has made.
- Distil. Heat the wash. Ethanol boils at 78.3°C and water at 100°C, so the vapour coming off is richer in alcohol than the liquid it left.
One thing to hold on to: every spirit leaves the still clear, and with no sweetness in it. Colour is wood, or caramel added afterwards. Sweetness is sugar added afterwards. A dark rum and a white rum can be the same distillate with different post-processing, and knowing that stops you paying more for colour.
Two kinds of still
A pot still is a batch process: fill it, run it, empty it, start again. It's inefficient on purpose. A single pass gets you to around 25–30%, so most pot-distilled spirits go through twice, landing near 75% before dilution. Because the separation is imperfect, plenty of heavier compounds come across with the alcohol, and those are flavour. Pot stills make characterful spirits: single malt, cognac, aged rum.
A column still runs continuously, with the wash fed in at the top and vapour rising through a stack of plates. Each plate is effectively another distillation, so one pass can reach 95%+. That's pure and correspondingly neutral. Column stills make vodka, most gin bases, and grain whisky.
Two kinds of still
| Pot still | Column still | |
|---|---|---|
| Runs | One batch at a time | Continuously |
| One pass gets to | 25–30% | Up to 96% |
| Usual practice | Distil twice, to ~75% | One pass is enough |
| Character | Carries flavour through | Strips flavour out |
| Typically makes | Malt whisky, cognac, aged rum | Vodka, gin base, grain whisky |
Most spirits are bottled somewhere between 37.5% and 40%, which means the distiller has added a lot of water to it. What you buy is a deliberate dilution of something much stronger.
After the still
- Maturation. Time in wood. Takes colour, tannin, vanilla and spice out of the barrel and rounds off the harsh edges. Legally required for some categories, forbidden for others.
- Colouring. Caramel, usually E150a. Legal nearly everywhere and used more than labels admit, because it makes batches match.
- Sweetening. Sugar or syrup. Common in rum and in anything calling itself a liqueur.
- Dilution. Pure water down to bottling strength.
Who owns the shelf
Strength and standard drinks
As built
27.0%
90 ml
As served
22.1%
110 ml
Standard drinks
1.92
10 g each
Pure alcohol
19.2 g
in the glass
A standard drink in New Zealand is 10 g of pure alcohol. Dilution changes the strength but not the number of standard drinks - the alcohol is all still there.