It’s the yeast we can do …
You need yeast to make whisky, it is one of the three elements by law to make scotch. BUT – does the yeast have an effect on flavours in new make spirit? Erm, what exactly is yeast? Yeast is a single-celled fungus which comes in different species. Yeast has the ability to mutate and breed to produce specific aromas – apple, mango or rose. The species mostly used for whisky is called Saccharomyces Cerevisiae, but there are many strains of this, all of which give different flavour profiles – a champagne yeast will be different to a red wine yeast, you still with me? I am starting to lose it myself – yeast eats sugar and produces alcohol, carbon dioxide and heat and in the process flavours are created. When yeast is added to the wort in a distillery, it starts to figure out its new environment – called the lag phase. It then starts to ‘bud’ or reproduce asexually, oh come on now! Vic, I need a hand here please. Eventually the sugar is used and the yeast dies. Distillers hold onto the wash in the wash back before sending it to the stills, as more flavours are now being generated by lactobacillus, wish I had carried on with Latin in school. Back in Scotland most distillers use M strains of S.cerevisiae have done since the 1950s. Today, a new super-strain of M, called MX, has the same qualities as the old strain but is quicker and more efficient I’m told by whisky insiders. Brewer’s yeasts have been phased out almost totally, efficiency is key to Scotch distillers and flavour creation shifted from yeast to other parts of the process. I have been reliably told a number of distillers in Scotland are now looking at yeast as a flavour tool. Meanwhile – expert time is here – Dr. Bill Lumsden, whose career started in yeast physiology ‘Yeast is one of the great unexplored areas of whisky flavour.’
So, a wee bit of delving later; yeast used during the fermentation process affects a whisky’s aromatic palette. Yeasts are single celled micro organisms from the mushroom family that feed on sugar, producing alcohol and carbon dioxide in the process. Hmmm, so if you suck a mushroom to the limit would you be downing alcohol? There are two categories of yeast: wild yeast and cultured yeast. Wild yeast is contained within the atmosphere and is still sometimes used to make craft beers. Cultured yeasts, are the most frequently used – in a complementary fashion. They allow alcohol content to be predicted in advance, and the production of specific aromas correspond to the aromatic profile of various types of whiskies. Even writing this I am again astounded of all the detail that goes into making a dram.
When the wash back is two-thirds full yeast is added to the mix. Once the yeast is activated, the sugar contained in the wort is transformed into alcohol and carbonic gas. The resulting liquid is known as the wash. It begins to bubble like an Aero bar, with its’ temperature rising from 20°C to 35°C. Rotating arms continuously stir the wash to ensure temperatures don’t rise too high, which would inhibit the yeast. It takes between forty and sixty hours to convert the sugar into alcohol, into a kind of malt beer with an alcohol content of between 6% and 8%. At this point it’s horrible to taste and can do you damage if you down too much of it. “The Saccharomyces yeast is a single-cell fungus, containing 16 different chromosomes and because its genome is diploid, there are 32 chromosomes containing the genome (DNA). It can reproduce by budding (producing a copy of genome and cell organs and dividing into two) or mating by spores.”. Now this goin too far and way over my head, so am ending it here, do you now know more, or totally confused? Me; am in the “wish I had not skipped school that much” section. PAUL MCLEAN