Feeling fruity: using new yeasts to develop alternative scotch flavours

Could the flavour of Scotch be altered by using different yeast for fermentation? A new research project at Abertay University seeks to find out. Elliot Gardner speaks to the project lead.


The Scotch whisky industry is famously rigorously regulated and protected, which prevents a great deal of innovation in the market. However, Graeme Walker of Abertay University’s Division of Food & Drink believes he’s found a method of developing new flavours for Scotch without contravening the Scotch Whiskey Act 1988 by experimenting with the yeast used as part of fermentation.

Walker’s research project will shortly be underway at Abertay University in collaboration with the Scotch Whisky Research Institute.

Elliot Gardner: Tell me more about the research project you’re running.

Graeme Walker: I'm a yeast scientist, so I’m interested in the role of yeast in beverage fermentations and a whole range of other applications. We've had a long-term collaboration with the Scotch Whisky Research Institute on various projects and we were mulling over potential areas where we could continue our collaboration. The subject of flavour complexity in new-make spirit was suggested.

There has been a method in the Scotch whisky industry to select yeasts that are very efficient in converting the available sugar into alcohol, but not those that might develop complex and interesting flavours that ultimately could be expressed in the final product after it has been matured.

My understanding of the Scotch whisky regulations and the Scotch Whiskey Act (1988) is that there is no real specification as to what type of yeast is to be used for the production. At the moment there is one type of yeast used, and that is strains of saccharomyces cerevisiae. I'm not saying these are bad yeasts, they’re highly efficient and produce wonderful alcohol and wonderful products. But its only one of hundreds, maybe even thousands of other strains of other yeast that may have interesting flavour expressions.

EG: How much involvement will the Scotch Whisky Research Institute have as part of the programme?

GW: They're very well set up for sensory analysis and for some of the more sophisticated chemical analysis. When we do appoint a PhD student to this research project they will be spending a chunk of their time actually in the labs of the institute, as well as working in the university labs as well, so it’s a true collaboration in that sense.

EG: How much of the flavour of whisky comes from the yeast?

GW: Where does whisky flavour come from? Obviously there are the raw materials, so the malt if it’s single malt whisky we're talking about, and the kilning temperature. People think water is also key to flavour but surprisingly the research that's been done on water concludes that the flavour of whisky is not really impacted dramatically by the source of water.

So the next thing is the processing of the whisky and the fermentation, where the yeast is going to be playing a key role in bringing out the congeners, the flavour compounds. Then there’s the distillation process, the type and configuration of the still, and the amount of copper that’s in contact with the spirit, that’s going to play a role, and also the ageing in wood.

Of these things I would maintain that the yeast and the fermentation is playing a pivotal role because in addition to the alcohol, the yeast is going to produce a whole array of flavour-active compounds that will find their way into the final spirit. If you were to ask me how many of these flavour compounds there were, nobody knows for sure, but potentially there are thousands of minor yeast compounds that are collectively going to contribute to the flavour and the aroma of the product.

EG: How will you choose the varieties of yeast you’ll experiment with?

GW: There are some interesting possibilities taken from other industries. Other fermented beverages have interesting flavours that are imparted by, in some cases, unusual yeasts.

Some of these yeasts are what we call wild yeasts, so they may not be purposely cultured but they may get into the fermentation due to an external, almost contamination-type process. Some of these from the wine industry have been known for quite a while - they're more unusual species of yeasts that produce interesting fruity aromas and flavours.

I think distillers are generally on the lookout for ester-y or fruity notes coming through in single malt scotch whiskies, perhaps not so much in the grain whiskies that form the base for blended whiskies. So these fruity compounds are desirable to bring out, to coin a phrase from the wine industry, a nice bouquet of the spirit.

EG: Is that what brings the flavour to wine?

GW: Obviously the type of grape is going to be important but again the yeast, through its fermentation activities, will produce a whole cocktail of these fruity esters. Every ester has a particularly fruity note, whether its gooseberry, pineapple, apricot, banana or whatever, there's normally an ester that’s contributing to that particular aroma or flavour.

EG: Do you expect any trouble with the Scotch Whisky Association?

GW: My colleagues in the Scotch Whisky Research Institute have a very close collaboration with the Scotch Whisky Association, and they wouldn’t have given the go-ahead for this research project if they thought in any way we'd be contravening any of the regulatory or legislative aspects surrounding Scotch whisky.

The only thing that they sometimes sniff at is the word 'non-traditional'. There's a whole series of things that people have tried over the years and the Scotch Whisky Association has said 'this is interesting but it’s not traditional so we won’t support this' - wacky things like preventing the angels’ share in the ageing by shrink-wrapping the barrels.

EG: Do you see any challenges that might crop up as part of the project?

GW: I think some of the yeast that we might look at might not be able to handle the sugars that are available in whisky fermentation; there’s a spectrum of different sugars that they have to be able to ferment. One of them is the sugar maltose, so I think any yeast that we look at would have to be able to ferment that.

The other thing that we might consider is rather than using these unusual varieties as the main yeast, we could look at the standard whisky yeast and then once fermentation gets going or perhaps towards the end, then maybe mix with some of these unusual yeasts to see if this brings out any interesting final aroma and flavour later in the process, like a sort of co-culturing exercise. I think that might prove interesting.

EG: So can we soon expect a wider range of Scotch on our shelves?

GW: Who knows, but of course to be called Scotch whisky it needs to be matured in an oak cask for a minimum of three years, so what we're going to be looking at is the raw spirit before it goes into maturation to see if there's any interesting complexity in the flavour from that spirit. The hope is that might be transferred into the final matured spirit. It’s kind of an unknown for us, which is what makes it interesting.