The Science of Whisky

In the spirit of British Science Week, here’s some interesting whisky science to satisfy the inner geek in you and supplement this week’s pub chat (over a whisky or beer, of course).

Why We Love Yeast

‘Mashing’ is a term used in the brewing and distilling industry to describe the process of mixing cereal grains with hot water to extract the cereal-based sugars. To this liquid we add yeast; a single-celled fungus that feeds on the sugars and excretes carbon dioxide and ethyl alcohol (aka ethanol, or simply alcohol) in a process termed anaerobic fermentation. Yeast is responsible for the alcohol in our beer & whisky but what about those fruity and floral flavours? Many other compounds are produced during fermentation, the most important of which are esters. Whilst occurring naturally in fruits and flowers, yeast-derived esters give beer and whisky much of its flavour, despite being present at very low levels. Different yeast strains give different flavour profiles, so next time you have hints of apples or banana in your whisky, remember it’s these esters you’re detecting. You have yeast to thank for that.

Bucket of live yeast

Bucket of live yeast

Fermentation under way

Fermentation under way

Head here for more fermentation-related science.

Photos taken at Treboom Brewery, Yorkshire.

Copper is King

Search ‘whisky distillery’ in Google and you’re inundated with images of shiny copper pot stills in all manner of shapes and sizes. Copper has been used for centuries in whisky distillation, but why? Aside from its malleability and good heat conductivity, copper has reactive properties which make it perfect for distilling grain and it continues to be the preferred material for use in whisky stills today.

As mentioned above, many desirable flavour compounds are produced during fermentation, but also some less-desirable ones, such as unpleasantly pungent sulphur-containing compounds. Copper is highly reactive and helps to remove these unwanted compounds from the spirit by reacting with sulphur to form copper salts which are left behind during distillation. In addition to removing unpleasant compounds, copper also acts as a catalyst for the formation of non-yeast-derived esters, contributing further fruity notes to the spirit. So, aside from providing a physical vessel in which to distil spirit, copper directly shapes the unique character of each distillery’s whisky.

Glen Moray stills

Glen Moray stills

Whisky and brandy still at Healey's Cyder Farm

Whisky and brandy still at Healey's Cyder Farm

Chill-Filtration - What Is It?

Chill filtration is an industrial process carried out after maturation and before bottling whisky, to remove certain particles that cause cloudiness when bottled at strengths of less than 46% alcohol by volume (abv).

The majority of this cloudiness – or haze – is due to long chain fatty acid esters present in the whisky. These esters are more soluble in alcohol than water, so that when whisky is bottled at high strengths (46% abv and above) the molecules remain in solution and the whisky appears clear. Whisky bottled below 46% abv contains enough water to cause the esters to precipitate out of solution, forming a haze. Most distilleries that bottle their whisky below 46% abv choose to chill-filter; chilling the spirit to below 10oC to encourage haze formation, then passing through a filter to remove the haze before bottling. Although preserving the clarity of the spirit, chill-filtration removes compounds that contribute to the overall flavour, texture and colour of the whisky. Loss of colour is often rectified by the addition of E150 artificial colouring - known as ‘spirit caramel’ - but flavour and texture can’t be replaced (we touch on colouring additives in our whisky myths blog). Even un-filtered whiskies bottled at above 46% abv may still form a haze at low temperatures or when diluted with water before drinking, but this is in no way detrimental to the enjoyment of the spirit.

At Cooper King Distillery we will never chill filter or colour our whisky, so that it retains all the natural complex malty character, texture and colour developed through its careful production and many years of maturation.