Glossary

The words of distilling and fermenting, explained plainly - 110 terms, from ABV to yeast. Search, filter by subject, and tap any underlined word to follow it to a related term. For the bigger picture, start with the Introduction or the guides.

110 terms

A

ABVMeasuring: Also: alcohol by volumeAlcohol by volume: the share of a liquid that is pure alcohol. A 40% ABV spirit holds 40 mL of alcohol in every 100 mL. US proof is double the ABV.
AgeingSpirits and flavour: Also: aging, barrel ageing, oakResting a spirit in contact with oak - in a barrel, or on staves or chips - so it draws out colour, vanilla and tannin while its harsher edges soften. Small pieces of oak work faster than a large barrel. Most whiskeys and dark rums are aged; vodka and gin are not.
AirlockEquipment: Also: bubblerA small one-way water valve in a fermenter lid. It lets carbon dioxide out while keeping air, insects and wild yeasts out. Bubbling shows that fermentation is active - but not when it has finished; only a hydrometer can tell you that.
AlarmStilligent: Stilligent's signal that something has gone wrong. Alarms are graded: a non-critical alarm warns of a problem that needs attention; a critical alarm cuts power to the boiler and can be set to call for help. Compare alert.
AlcoholmeterMeasuring: Also: alcometer, spirit hydrometer, proof and tralleA glass float, like a hydrometer, marked to read the ABV of a spirit directly. Most are calibrated at 20 °C, so readings at other temperatures need correcting. It cannot read a wash: dissolved sugar upsets it.
AlertStilligent: A routine signal that you are needed - a bottle swap, or a finished run. Alerts sound a gentle chime and never trigger the siren. Compare alarm.
AmylaseFermenting: Also: enzymes, alpha-amylase, beta-amylaseThe enzymes that break starch into fermentable sugars. Alpha-amylase chops long starch chains into shorter pieces; beta-amylase snips off maltose, the sugar yeast ferments. Malted grain supplies them naturally; bought enzymes do the same job. See conversion.
Angel's shareSpirits and flavour: The spirit that evaporates through the wood while it ages in a barrel - typically a few percent a year, more in a warm, dry climate.
AttenuationFermenting: How much of the sugar the yeast has fermented, shown by how far the gravity has fallen. A sugar wash that finishes at about 0.990 is fully attenuated; one that stops at 1.010 still has sugar in it.
AzeotropeDistilling: A mixture that boils without changing its make-up. Ethanol and water form one at about 96% ABV, which is why ordinary distillation cannot produce purer alcohol. At sea level it boils at about 78.2 °C, a fraction below pure ethanol.

B

BacksetFermenting: Also: setback, spent washSome of the hot liquid left in the boiler after a run - the stillage - cooled and used in place of part of the water in the next wash. It adds acidity, nutrients and flavour, and keeps one batch like the last: it is the heart of a sour mash. A quarter to a half of the liquid is typical; more can make the wash too acidic. Rum makers call it dunder.
Bain-marieEquipment: Also: water bath, jacketed boiler, double boilerA boiler heated through a jacket of water or oil rather than directly, so thick washes such as grain or fruit mashes heat gently and don't scorch.
BoilerEquipment: Also: pot, kettleThe heated vessel that holds the wash - also called the pot or kettle. Heat usually comes from an electric element or a flame.
BotanicalsSpirits and flavour: The plant ingredients that flavour gin: juniper above all, with coriander seed, citrus peel, angelica and orris root, spices and herbs. They are macerated in the spirit or held in a vapour basket.
BrixMeasuring: Also: °Bx, degrees Brix, PlatoA scale of dissolved sugar, in percent by weight; refractometers usually read in it. As a rough guide, one degree Brix is about four gravity points, so 1.060 is about 15 °Bx. Brewers' degrees Plato are almost the same.
BufferFermenting: Also: pH bufferAnything in a wash that resists a change in pH - the minerals, proteins and salts in grain, molasses or tomato paste, or chalk added on purpose. Sugar washes have very little, so their pH can fall far enough during fermentation to slow or stop the yeast.

C

Calcium carbonateFermenting: Also: chalk, eggshells, CaCO3Chalk: the usual buffer for a sugar wash. It dissolves only while the wash is acidic, so it is hard to overdo, and it keeps neutralising acid as fermentation produces it. Clean, crushed eggshells are mostly calcium carbonate and do the same job more slowly.
CapFermenting: Also: grain cap, fruit capThe raft of grain, fruit or foam pushed to the top of a fermenting wash by rising carbon dioxide. Stirring it back in or punching it down keeps it from drying out and spoiling.
ChargeDistilling: The liquid loaded into the boiler for a run - a wash, low wines, or low wines with feints. Fill to no more than about 80% of the boiler, to leave headspace.
ClearingFermenting: Also: settling, clarifyingLetting a finished wash stand so that yeast and solids settle to the bottom as lees. A clear wash distils more cleanly and is less likely to scorch or puke.
ColumnEquipment: The tube above the boiler that vapour rises through. In a reflux still it is filled with packing or fitted with plates to improve separation.
Column headEquipment: Also: still headThe top of the column, where vapour leaves for the condenser - and where the key temperature, the head temperature, is measured.
CondenserEquipment: Also: Liebig, shotgun condenser, worm, coilA section cooled by water or air that turns the vapour back into liquid. Common designs are the Liebig (a tube inside a water jacket), the shotgun (many small tubes in one jacket) and the traditional worm, a coil in a tub of water.
CongenersSpirits and flavour: Everything in a spirit besides alcohol and water - the flavour compounds, such as esters, aldehydes and fusel oils. Some are wanted, others are not, which is why cuts matter.
ConversionFermenting: Also: saccharification, starch conversionIn a grain mash, the breaking down of starch into fermentable sugars by amylase enzymes, usually held at about 63–68 °C. The iodine test shows when it is complete.
CopperEquipment: The traditional metal for stills, and not only for looks: copper reacts with the sulphur compounds yeast produces - the rotten-egg and struck-match smells - and removes them from the spirit. Even a stainless still benefits from some copper in the vapour path, such as copper packing.
CutsDistilling: Dividing what comes out of the still into foreshots, heads, hearts and tails, and keeping only the best part for drinking.

D

DAPFermenting: Also: diammonium phosphate, yeast nutrientDiammonium phosphate: a common yeast nutrient that supplies nitrogen and phosphorus, which sugar washes lack. As the yeast takes up its ammonium it releases acid, so DAP-fed washes tend to lower their own pH. Use only what the recipe calls for.
DephlegmatorEquipment: Also: dephleg, partial condenserA small condenser at the top of a column that turns part of the vapour back into liquid. Adjusting its cooling sets the reflux ratio - and so the strength and purity of the spirit.
Diastatic powerFermenting: Also: DP, LintnerA malt's ability to convert starch into sugar - a measure of its enzymes. Pale malts, especially six-row barley, have plenty and can convert unmalted grains such as corn alongside them; roasted malts have none.
Distiller's yeastFermenting: Also: distiller's yeast, DADYYeast strains chosen for distilling: they tolerate more alcohol and higher temperatures than bread yeast, and ferment sugar and grain washes quickly and cleanly.
DunderFermenting: The rum maker's name for backset: the spent wash left in the still, added to the next molasses wash for acidity, nutrients and flavour.

E

ElementEquipment: Also: heating element, immersion heaterAn electric heater that sits in the wash inside the boiler. Its real power depends on the supply voltage: a 3,000 W, 230 V element gives only about 2,750 W at 220 V.
Epsom saltsFermenting: Also: magnesium sulphateMagnesium sulphate. A pinch supplies the magnesium yeast needs; many sugar-wash recipes include it.
EstersSpirits and flavour: Fruity, flowery compounds formed when acids and alcohols combine, during fermentation and in the still. Ethyl acetate, which smells of nail-polish remover, gathers in the heads; heavier, fruitier esters run through the hearts and into the tails.
EthanolSpirits and flavour: Also: ethyl alcohol, alcohol, EtOH, C2H5OHThe alcohol in drinks (C₂H₅OH), made by yeast as it ferments sugar. Pure ethanol boils at 78.4 °C at sea level, well below water's 100 °C - the difference distillation relies on. It mixes with water in any proportion, though the mixture takes up slightly less room than its parts, and it cannot be distilled beyond about 95.6% ABV, where it boils together with water as an azeotrope. Its vapour is flammable, even from spirit at room temperature - one reason a still must never be left unattended.

F

FeintsDistilling: Heads and tails kept together to be added to a later run and distilled again, so the alcohol in them isn't wasted.
FermentationFermenting: Yeast turning sugar into ethanol and carbon dioxide, along with heat and small amounts of flavour compounds. A sugar wash takes about one to two weeks; a fast recipe, a few days.
FermenterEquipment: Also: fermenting bucket, carboy, demijohnThe vessel a wash ferments in - usually a food-grade plastic bucket or drum, a glass carboy or a stainless tank, with a lid and an airlock. Leave plenty of headspace for foam.
Final gravityMeasuring: Also: FG, terminal gravityThe gravity of a wash when fermentation has finished. Sugar washes usually end at about 0.990–0.995; grain and molasses washes finish higher. Two identical readings a day or two apart confirm it has finished.
FlocculationFermenting: Yeast cells clumping together and settling out when fermentation ends. Strongly flocculating yeasts give a clear wash sooner.
ForeshotsDistilling: The very first liquid off the still, full of volatile solvent-like compounds including any methanol. Never for drinking.
Fusel oilsSpirits and flavour: Also: fusels, higher alcoholsHeavier alcohols, such as propanol and amyl alcohols, that taste harsh and oily. Yeast makes more of them when it is stressed or too warm. They concentrate in the tails.

G

GelatinisationFermenting: Also: gelatinization, cooking grainCooking grain in hot water until its starch granules swell and burst, so enzymes can reach the starch. Corn needs near-boiling water; barley and wheat gelatinise at much lower temperatures.
GinSpirits and flavour: Also: London dry, compound ginNeutral spirit flavoured with juniper and other botanicals - either by redistilling it with them (distilled gin) or simply steeping them in it (compound gin).
Grain billFermenting: Also: mash billThe list of grains, by proportion, in a mash - for example 70% corn, 20% rye and 10% malted barley. US bourbon must be at least 51% corn.
GravityMeasuring: Also: specific gravity, SG, pointsSpecific gravity: a liquid's density compared with water's, read with a hydrometer. Dissolved sugar raises it; alcohol lowers it. Readings are written like 1.065 - or "65 points". The original and final gravity together give the wash's ABV.
GypsumFermenting: Also: calcium sulphateCalcium sulphate, from brewing suppliers. A little adds calcium for the yeast, especially in soft water.

H

Head temperatureMeasuring: Also: vapour temperature, column head temperatureThe temperature of the vapour at the column head. It shows what is coming over: close to 78 °C, nearly pure alcohol; rising, more water and heavier compounds. Stilligent reads it continuously.
HeadsDistilling: The portion after the foreshots: sharp, solvent-like and unpleasant. Set aside, often as feints.
HeadspaceEquipment: Also: ullageThe empty space left above the liquid in a fermenter or boiler. Fermenting washes can foam far above their starting level; a boiler should be no more than about 80% full.
HeartsDistilling: Also: body, middle cutThe middle of the run - also called the body. The clean, good-tasting spirit the run is for.
Heating power regulatorStilligent: Also: power regulatorThe electronic switch that sets the heating element's power, from 0 to 100%, during a run.
HydrometerMeasuring: Also: saccharometerA weighted glass float that reads the gravity of a wash. Take a reading before and after fermentation to work out the strength. It cannot measure spirit - that needs an alcoholmeter.

I

InfusionSpirits and flavour: Also: steeping, liqueurFlavouring a finished spirit by steeping fruit, herbs, spices or wood in it, without distilling it again.
InvertaseFermenting: The enzyme that splits sucrose into glucose and fructose. Yeast makes its own, so it inverts table sugar by itself within hours of pitching.
Inverted sugarFermenting: Also: invert sugar, invert syrup, invertingTable sugar (sucrose) split into glucose and fructose, by simmering it with water and a little acid. It gives the yeast a quicker start, but no more alcohol - and the acid stays in the wash. See the guide to inverted sugar.
Iodine testMeasuring: Also: starch testA drop of iodine on a little mash liquid on a white plate. Blue-black means starch remains; no change of colour means conversion is complete. Throw the sample away afterwards.

J

JarsDistilling: Also: jarring, jar methodCollecting a run in many small, numbered jars instead of one vessel, so the cuts can be decided afterwards by smell and taste. See the guide to making the cuts.

K

Kahm yeastFermenting: Also: kahm, film yeast, flowers of wine, surface yeastA thin, white to cream film - flat or finely wrinkled - that wild yeasts form on the surface of a wash, brine or ferment left open to the air, usually once fermentation has finished and the protective blanket of carbon dioxide has gone. It is not mould: mould is fuzzy, raised and often coloured. Kahm yeast is harmless, but it feeds on alcohol and can bring stale, solvent-like flavours. Skim it off and distil the wash soon; prevent it by keeping fermenters sealed under an airlock, keeping headspace small and working clean.
KrausenFermenting: Also: kräusenThe rocky, foamy head that forms on a wash at the height of fermentation, and falls back as it slows.

L

Lag phaseFermenting: The quiet hours after pitching while the yeast adapts and multiplies, before fermentation visibly starts. Usually a few hours to a day; a long lag gives bacteria a chance.
LeesFermenting: Also: trub, sedimentThe sediment of yeast and solids at the bottom of a finished wash. Rack the wash off it before distilling.
LoucheSpirits and flavour: Also: cloudy spiritCloudiness that appears when a spirit is diluted, as oils come out of solution. Expected in anise drinks; in a neutral spirit it usually means tails found their way into the hearts.
Low winesDistilling: The stronger, rougher liquid produced by a stripping run - often roughly 25–40% ABV - ready for a spirit run.
Lyne armEquipment: Also: lye arm, swan neckThe pipe that carries vapour from the top of a pot still to the condenser. Its angle and length change how much reflux there is: an arm that rises gives a lighter spirit; one that falls, a heavier one.

M

MacerationSpirits and flavour: Also: steepingSteeping botanicals or fruit in spirit for hours or weeks to draw out flavour - before distilling, as for gin, or as an infusion.
MaltFermenting: Also: malted barley, maltingGrain, usually barley, that has been soaked, allowed to sprout and then dried. Sprouting develops the enzymes that turn starch into sugar.
MashFermenting: Also: mashingGrain cooked in water and held at the right temperature so that its starch converts into sugar - and, in everyday use, the grain wash that ferments from it. Compare wash.
MethanolSpirits and flavour: Also: methyl alcohol, wood alcoholA toxic alcohol that comes mainly from the pectin in fruit, not from sugar or grain. It boils at 64.7 °C but spreads through the run rather than coming off all at once. See the methanol guide.
MolassesFermenting: Also: blackstrap, treacle, feed molassesThe thick, dark syrup left after sugar is refined from cane or beet: the base of most rum. About half of it is fermentable sugar; the rest includes minerals that feed and buffer the wash. Blackstrap is the final, darkest grade.
MoonshineSpirits and flavour: Also: white lightning, white dogTraditionally, illicitly distilled spirit; today, mostly unaged corn whiskey or any clear, unaged spirit sold under the name.

N

Neutral spiritSpirits and flavour: Also: NGS, rectified spiritAlcohol distilled to a high strength - around 95% ABV - so that little flavour remains. The base for vodka, gin and liqueurs.
NutrientsFermenting: Also: yeast nutrientThe nitrogen, minerals and vitamins yeast needs besides sugar. Grain and molasses supply them; a sugar wash needs them added - as DAP, Epsom salts, tomato paste, bran or a commercial nutrient.

O

Original gravityMeasuring: Also: OG, starting gravityThe gravity of a wash before fermentation, showing how much sugar it holds. With the final gravity, it gives the strength.
Osmotic stressFermenting: Also: high gravityThe strain a very sugary wash puts on yeast by drawing water out of its cells. It slows the start and encourages off-flavours - a reason to keep to a recipe's gravity.

P

PackingEquipment: Also: copper mesh, scrubbers, saddles, raschig ringsMaterial that fills a reflux column - copper mesh, stainless scrubbers or ceramic saddles - giving rising vapour and falling liquid a large surface on which to meet.
ParrotEquipment: A small fitting under the still's outlet that holds an alcoholmeter in the flowing spirit, so its strength can be read as it runs.
pHMeasuring: Also: acidity, pH meter, pH stripsA measure of acidity, from 0 (very acidic) through 7 (neutral) to 14. Yeast ferments best at about pH 4–5. A sugar wash's pH falls as it ferments, and below about 3.5 fermentation slows. Measure it with test strips or a calibrated meter.
PitchingFermenting: Adding yeast to a wash. Dried yeast is best rehydrated in warm water first, and the wash should be within the yeast's temperature range.
PlatesEquipment: Also: bubble caps, sieve plates, traysPerforated trays stacked in a column, each holding a little liquid that the vapour bubbles through. Each plate acts like a small distillation of its own; more plates give a stronger, lighter spirit.
Pot stillEquipment: Also: alembic, alembic stillThe simplest still: a boiler, a head, a lyne arm and a condenser. With little reflux it keeps much of the wash's flavour, and usually needs two runs. See pot still vs reflux still.
ProofMeasuring: An older way of stating alcohol strength. In the US, proof is simply double the ABV, so a 40% ABV spirit is 80 proof. The traditional British scale differs: 100° proof is about 57% ABV.
PukingDistilling: Also: puke, foaming overWhen boiling wash foams up into the column or arm and comes out with the spirit. Overfilling, too much heat or a foamy, uncleared wash are the usual causes. It spoils the collected spirit and can block the vapour path.

R

RackingFermenting: Also: siphoningSiphoning a wash off its lees into a clean vessel or the boiler, leaving the sediment behind.
RectificationDistilling: Purifying a spirit by repeated evaporation and condensation in a column, as a reflux still does in a single run.
RefluxDistilling: Vapour that condenses inside the column and runs back down to be re-evaporated. Each round trip purifies the vapour a little more.
Reflux ratioDistilling: How much of the condensed liquid is returned down the column compared with how much is collected. A higher ratio gives a purer, stronger spirit, more slowly.
Reflux stillEquipment: Also: column stillA still with a column built for plenty of reflux, producing a strong, clean spirit - up to about 95% ABV - in a single run.
RefractometerMeasuring: A small optical instrument that reads sugar content from a few drops, usually in Brix. Ideal before fermentation; once alcohol is present its readings need a correction, so use a hydrometer for the final gravity.
RumSpirits and flavour: Spirit made from sugar cane - usually molasses, sometimes cane juice or syrup. It may be bottled clear or aged.
RunDistilling: One complete distillation, from a cold boiler to the end of collection. Typically several hours.

S

ScorchingDistilling: Also: burning, scorchedSugar or solids burning on the element or the boiler floor, giving the spirit a burnt taste. Rack or strain thick washes, or heat them in a bain-marie.
Sour mashFermenting: Starting each new wash with backset from the last run. It lowers the pH, adds flavour and makes batch after batch alike; each repeat is called a generation.
Spirit runDistilling: The careful run, usually on low wines (or directly on a wash in a reflux still), in which the output is separated into cuts.
StillEquipment: Any apparatus for distilling: a boiler to heat the wash, a vapour path, and a condenser to turn the vapour back into liquid.
StillageDistilling: Also: spent wash, slopWhat is left in the boiler after a run: water, spent yeast, solids and acids. Reused, it becomes backset or dunder.
Stripping runDistilling: A fast first run that concentrates the alcohol in a wash into low wines. Cuts aren't made carefully at this stage.
Stuck fermentationFermenting: Also: stalled fermentation, stuck washA fermentation that stops before the sugar is used up. Common causes are a wash that is too cold or too hot, a pH that has fallen too low, too few nutrients, or more sugar than the yeast can tolerate.
Sugar washFermenting: Also: TPW, tomato paste washA wash made from white sugar, water, nutrients and yeast - the usual base for a clean neutral spirit. See the Birdwatchers recipe.

T

TailsDistilling: The final portion: weaker, oily and heavy, as water and higher-boiling compounds come over.
ThermowellEquipment: A small sealed metal pocket that holds a temperature sensor, so it can read a vessel's temperature without sitting directly in the liquid or vapour.
ThumperEquipment: Also: doubler, thump kegA vessel between the boiler and the condenser, partly filled with liquid, that the vapour bubbles through with a characteristic thump. It acts as a second distillation in the same run. A doubler does the same job dry, collecting liquid as it goes.
Turbo yeastFermenting: Yeast packed with heavy doses of nutrients for very fast, very strong washes - up to about 20% ABV. Quick, but usually at the cost of a harsher flavour.

V

Vapour basketEquipment: Also: gin basket, carter headA perforated basket in the vapour path that holds botanicals, so the rising vapour picks up their aroma - a lighter, fresher way to flavour gin than steeping.
VodkaSpirits and flavour: Neutral spirit diluted to drinking strength, often filtered, with as little flavour as possible.

W

WashFermenting: Also: beer, distiller's beerThe fermented liquid that goes into the still - also called the beer, or a mash when it is made from grain. Typically 8–15% ABV.
WatchdogStilligent: Also: Smart WatchdogA timer that expects a regular sign of life from another part of the system. If that signal stops - because something has crashed, frozen or lost its connection - the watchdog acts on its own and cuts power to the boiler. Stilligent uses three, one at each level; the last is built into the Smart Watchdog, an independent hardware device on the boiler's supply.
WhiskeySpirits and flavour: Also: whisky, bourbon, ryeSpirit distilled from a fermented grain mash and usually aged in oak. Spelt whisky in Scotland, Canada and Japan, and whiskey in Ireland and the US.

Y

YeastFermenting: Also: Saccharomyces, bread yeast, baker's yeast, wine yeastThe single-celled fungus - Saccharomyces cerevisiae - that ferments sugar into alcohol. Bread yeast, wine yeast, distiller's yeast and turbo yeast differ in how much alcohol they tolerate, the temperatures they like and the flavours they leave.