A
- ABV
- Alcohol by volume: the percentage of a liquid’s volume that is pure ethanol, measured at a reference temperature of 20°C. ABV Dilution Calculator →
- Acetaldehyde
- A sharp, green-apple-smelling aldehyde produced during fermentation and concentrated in the foreshots. Responsible for much of the harshness the foreshots discard removes. How to Make Cuts →
- Adjunct
- Any unmalted fermentable added to a mash, such as corn, rice or plain sugar, that relies on malt or added enzymes for conversion.
- Airlock
- A one-way valve on a fermenter that vents carbon dioxide while blocking air and contaminants.
- Apparent attenuation
- The percentage of gravity drop during fermentation, calculated from hydrometer readings without correcting for alcohol’s effect on them. Fermentation ABV Calculator →
- Azeotrope
- The composition at which ethanol and water boil as a fixed mixture, near 97% ABV, setting the ceiling for distillation strength. Proof & ABV Guide →
B
- Backset
- Acidic liquid left in the still after a run, added to the next mash to lower pH and buffer it. The basis of sour mashing. Sour Mash Guide →
- Balling
- The 19th-century extract scale and set of relationships linking wort gravity, extract and alcohol, underlying most ABV formulas.
- Boiler
- The heated vessel of a still that holds the charge.
- Brix
- A scale expressing grams of sucrose per 100 g of solution; the refractometer’s native unit. Brix to SG Converter →
C
- Charge
- The wash or low wines loaded into a still for a run.
- Chill filtration
- Chilling spirit so haze-forming esters precipitate, then filtering them out cold so the spirit stays bright when diluted or iced. Why Spirits Go Cloudy →
- Congeners
- Collective term for everything in a spirit that is not ethanol or water: esters, higher alcohols, aldehydes, acids and more. The flavour, for better and worse.
- Cuts
- The decisions dividing a spirit run into foreshots, heads, hearts and tails. Cuts Calculator →
D
- Dephlegmator
- A small condenser at the top of a column that returns part of the vapour as reflux, controlling purity.
- Dextrins
- Longer sugar chains left by mashing that yeast cannot ferment; the reason beer rarely finishes below 1.008. Beer ABV Calculator →
- Distillers beer
- Another name for a fermented grain wash destined for the still.
- Dunder
- Rum-world term for backset, often deliberately aged to build ester precursors.
E
- Entry proof
- The ABV at which spirit is filled into a barrel; it steers which oak compounds extract fastest. Barrel Entry Proof Guide →
- Esters
- Aromatic compounds formed from acids and alcohols; the source of most fruity notes in spirits. Esters Guide →
- Ethyl acetate
- The most abundant spirit ester: pear drops in small amounts, nail polish in excess. Concentrates in the heads.
- Ethyl carbamate
- A trace compound monitored in commercial stone-fruit spirits, formed from natural cyanide precursors in pits.
F
- Feints
- The combined heads and tails saved from a run and recycled into a future spirit run. Feints Guide →
- Fermentation
- The conversion of sugars to ethanol and carbon dioxide by yeast. Fermentation Calculator →
- Final gravity (FG)
- The specific gravity of a wash when fermentation is complete.
- Foreshots
- The first fraction off the still, concentrated in acetaldehyde and ethyl acetate. Always discarded. Cuts Guide →
- Fusel alcohols
- Higher alcohols produced by yeast from amino acids; oily and harsh in excess, part of a spirit’s character in moderation. Fusel Alcohol Guide →
G
- Grain bill
- The recipe of grains making up a mash, usually expressed in weights and percentages. Grain Bill Calculator →
- Gravity
- Shorthand for specific gravity: the density of a liquid relative to water, used to track sugar and fermentation progress.
H
- Heads
- The early fraction after foreshots, rich in ethyl acetate and light volatiles. Partly kept or recycled by style.
- Hearts
- The middle fraction of a spirit run: the keeper.
- Heel
- Liquid deliberately or accidentally left in the boiler at the end of a run.
- Hydrometer
- A float instrument reading liquid density: gravity hydrometers for wash, alcoholmeters for spirit. Hydrometer Guide →
I
- Inulin
- The fructose-based storage carbohydrate of agave, unfermentable until hydrolysed by cooking or enzymes. Agave Guide →
- Iodine test
- A drop test for mash conversion: iodine stays amber when starch is fully converted, turns blue-black when it is not.
L
- Lautering
- Separating sweet wort from spent grain after mashing.
- Low wines
- The product of a stripping run: everything collected, typically 20 to 35% ABV, awaiting the spirit run.
- Louching
- Clouding caused by oils and long-chain esters dropping out of solution as strength falls, typically below about 46% ABV. Louching Guide →
- Lyne arm
- The pipe carrying vapour from the still head toward the condenser; its angle influences natural reflux.
M
- Maillard reactions
- Browning chemistry between sugars and amino acids during cooking and toasting; a major flavour source in cooked mashes and toasted oak.
- Mash
- Grain, water and heat combined so enzymes convert starch to fermentable sugar; also the verb for doing it. Mash Temperature Guide →
- Methanol
- A simple alcohol formed from pectin breakdown, not by yeast. Present at low levels in fruit ferments, essentially absent from clean sugar washes. Distilling Myths, Tested →
N
- Neutral spirit
- Spirit distilled and treated to near-flavourless purity, the base for vodka, gin and liqueurs. Neutral Spirit Guide →
- New make
- Freshly distilled spirit before any barrel time.
O
- Original gravity (OG)
- The specific gravity of a wash before fermentation begins.
- OIML tables
- The international alcoholometric tables relating density, temperature and alcoholic strength; the basis of accurate ABV measurement. Proof Converter →
P
- Parrot
- A collection fitting that keeps an alcoholmeter floating in the outflow for continuous strength reading.
- Pectin
- A plant polysaccharide, abundant in fruit, whose enzymatic breakdown releases methanol.
- pH
- The acidity scale governing enzyme activity, yeast health and infection resistance throughout fermentation. pH Guide →
- Pitching
- Adding yeast to a wash.
- Plato
- A refinement of the Balling extract scale; degrees Plato express grams of extract per 100 g of wort.
- Proof
- A legal strength scale: in the US, exactly twice the ABV at 60°F. Proof Converter →
- Puke / puking
- A still boiling over so foam and liquid wash carry into the vapour path and contaminate the distillate.
R
- Racking
- Transferring liquid off sediment into a clean vessel.
- Reflux
- Vapour condensed inside the still and returned downward, re-distilling as it meets rising vapour; the mechanism of purity. Reflux vs Pot Guide →
- Refractometer
- An optical instrument reading sugar content from light bending; needs correction once alcohol is present. Refractometer Calculator →
- Rummager
- A rotating chain in direct-fired commercial stills that prevents scorching; the reason home direct heat needs care with thick mashes.
S
- Sacrificial copper
- Copper mesh or packing placed in the vapour path of a stainless still to capture sulphur compounds. Copper vs Stainless →
- Sparge
- Rinsing sugars from spent grain with hot water after mashing.
- Specific gravity (SG)
- Density relative to water at a reference temperature; 1.050 means 5% denser than water.
- Spirit run
- The slow, careful distillation of low wines where cuts are made.
- Stripping run
- A fast first distillation of wash into low wines, run hot with no cuts.
- Stuck fermentation
- A fermentation that stops before the expected final gravity, from stress, starvation or temperature shock. Troubleshooting Guide →
- Sour mash
- A mash acidified with backset from a previous run. Sour Mash Guide →
T
- Tails
- The late fraction of a run, watery and fusel-heavy, saved as feints or discarded.
- Thumper
- A vapour-fed secondary vessel adding roughly one extra distillation stage to a pot still. Thumper Simulator →
- TOSNA
- A staggered nutrient protocol originally for mead, dosing nitrogen across the first half of fermentation. TOSNA Guide →
- Turbo yeast
- A packaged blend of aggressive yeast and heavy nutrients built for fast, strong sugar washes at a congener cost. EC-1118 vs Turbo →
V
- Vapor speed
- How hard a still is pushed, usually managed via power input; high speed blurs separation between fractions.
- Volumes of CO2
- The carbonation unit: litres of dissolved gas per litre of liquid. Priming Calculator →
W
- Wash
- Any fermented liquid destined for distillation.
- Wort
- The sweet liquid drawn from a mash before fermentation; once pitched, it becomes a wash.
Y
- YAN
- Yeast assimilable nitrogen: the nitrogen fraction yeast can actually use, the limiting nutrient of sugar and honey washes. Nutrient Calculator →
- Yeast pitch rate
- The quantity of viable yeast added per litre of wash; underpitching drives fusel production. Yeast Guide →