Esters in new make spirit

What esters are and why they matter

An ester forms when an alcohol joins with an acid. In a distillery, the alcohols are ethanol and the higher alcohols. The acids are mostly fatty acids made by yeast. The result is a family of compounds that smell of fruit and flowers, often at very low concentrations.

In new make, esters supply much of the character people call fruity, light or floral. In a mature whisky they remain part of the backbone under the cask. A spirit that goes into the cask thin on esters rarely comes out fruity, whatever the wood.

Esters are also the part of the house style a distillery can change fastest. Cask programmes take years to show results. A change in yeast, fermentation temperature or cut points shows up in the next week's new make.

The esters you will meet

• Ethyl acetate: pear drops and solvent. Pleasant at low levels, nail varnish when high. The most abundant ester in most spirits.
• Isoamyl acetate: banana and pear sweets.
• Ethyl hexanoate (ethyl caproate): green apple and aniseed.
• Ethyl octanoate and ethyl decanoate: waxy, fruity and soapy as they get heavier.
• Long-chain fatty acid esters such as ethyl dodecanoate: oily and waxy. They also cause haze when whisky is chilled or diluted.

Light esters come over early in a spirit run. Heavier ones come later. That one fact links fermentation, distillation and filtration.

Made in the fermenter

Yeast makes esters inside the cell from acetyl-CoA and alcohols using enzymes, then releases them into the wash. The amount depends on yeast strain, wort composition, temperature and oxygen. Warmer fermentation usually means more esters. Very high gravity worts can push ester production up as well, as brewers of strong beers know.

A longer fermentation adds another layer. After the yeast has finished, lactic acid bacteria in the wash produce acids. Those acids form further esters in the still and during maturation. Many distillers link long fermentations with a fruitier, more complex new make. Our guide to fermentation length and new make covers this in detail.

Distilled and concentrated

Esters are volatile. The still concentrates them along with ethanol. Copper contact in the still also matters. More copper contact strips sulphur compounds and lets fruity esters show more clearly. A tall still with a gentle reflux returns heavier compounds to the pot and passes lighter, fruitier spirit forward.

Heat input matters too. A slow, gentle run tends to give a cleaner, lighter spirit. Pushing the still hard drags heavier compounds over earlier.

The wash still and spirit still play different roles. The wash still strips alcohol and volatiles from the fermented wash into low wines at roughly 20 to 25% ABV. The spirit still separates those low wines into heads, heart and tails. Esters pass through both, so a change in either still shows up in the new make.

Cut points decide what you keep

In a pot still spirit run, the early fraction is the foreshots or heads. It is rich in ethyl acetate and other very volatile compounds, plus methanol. The middle cut, or heart, is the spirit you keep. The tail, or feints, carries heavier compounds including long-chain esters and fusel alcohols.

Move the start of the heart earlier and you keep more light esters and some solvent edge. Move the end later and you keep more waxy, oily esters and some heavier off notes. Many Scotch distilleries collect their heart somewhere in the region of 75% down to 60 to 65% ABV, but every distillery sets its own points. Our guide to new make strength and cut points covers the method.

How to measure what you are making

A craft distillery rarely has a gas chromatograph on site. It does not need one every day. A trained nose and a routine do most of the work. Nose the run at fixed intervals, recording strength and time. Dilute each sample to around 20% ABV in clean water before nosing. Note where pear drop and banana peak and where waxy and oily notes arrive. Send a few samples to an outside lab now and then to calibrate your nose against real numbers.

In a hot Indian fermenting room, wash temperature can climb fast. If your esters swing from batch to batch, check fermentation temperature logs before blaming the still.

Esters in the cask

Esters keep changing during maturation. Slow oxidation turns some ethanol into acetic acid, which forms more ethyl acetate. Other esters break down or react with wood compounds. In a hot warehouse the cask gives up its own flavours faster than these slow reactions move. A delicate, estery spirit can be covered by wood if left too long in an active cask. That makes matching cask to spirit part of managing esters.

Run one nosing ladder

On your next spirit run, take a 50 millilitre sample every few minutes from the first drops to the end of feints. Label each with time and strength. Dilute and nose them in order the next morning. Mark where you would cut. Compare that with where you actually cut. The gap is your first lesson in how cut points shape the esters you bottle years later.

Common questions

What are esters in whisky?

Fruity and floral compounds formed when an alcohol combines with an acid. Yeast makes most of them during fermentation and the still concentrates them.

Which ester smells of pear drops?

Ethyl acetate. At low levels it is fruity. At high levels it smells like solvent or nail varnish.

Does a longer fermentation make more esters?

Often yes. After yeast finishes, bacteria in the wash produce acids that form more esters during distillation and maturation.