Location, location, location

Q: Hi Dr Andy, Is there any way to predict the characteristics of a whisky’s maturation in hotter climates, compared with those matured in Scotland? For example, would five years ageing in tropical Goa in India be the approximate equivalent of 15 years in chilly Speyside?
Cheers, Tomasz George, Member 101****

Hi Tomasz, I would certainly expect whisky to ‘mature’ (I’ll come back to why I’ve used those ‘’s) much faster in Goa, where average temperatures are significantly warmer than in Speyside. Theory predicts this, and we also know this from empirical evidence – bourbon, for example, matures much more quickly in warmer Kentucky than Scotch does in the Highlands.

Laboratory experiments back this up. Higher temperatures increases the in-vitro rate of extraction of colour and flavour compounds from the wood into the spirit and the removal of sulphur compounds, which contribute to immature character. This is probably because increased temperature causes deeper penetration of spirit into the wood and access to colour and flavour.

I’m not confident we can say five years in Goa is ‘equivalent’ to 15 years in Speyside though. While the hotter temperatures would increase interaction with wood, you won’t necessarily get an equivalent increase in the rate of chemical reactions in the spirit. These reactions are important as they convert alcohols and acids into fruity/floral-tasting esters and contribute to the complexity of flavour. So, while you can force the woody, sweet flavours out of the wood quicker in Goa, you probably can’t create the same complexity of a long and slowly aged whisky from Scotland.

Studying any aspect of maturation is challenging because of the timescales involved and the difficulties of working with casks in warehouses and controlling the conditions – you wouldn’t be popular with the warehouse workers either! That said, the Scotch Whisky Research Institute has used temperature-controlled chambers to study full-sized casks and it is possible to model the effect of temperature on maturation in-vitro.

Model systems in the lab allow us to speed up maturation and do things on a much smaller, more practical scale. For example, to look at the effect of temperature on the extraction of colour or flavour, the quickest way is to use oak wood shavings/sawdust which gives a very large surface area to extract from.

We can do the same thing with powdered cask char scraped from the inner surface from the cask to look at the removal of sulphur compounds and immature character. Using wood sticks or blocks is better, as the structural integrity of the wood is preserved, and mini casks, which ‘breath’, allow us to represent more accurately what happens in a real cask.

Having modelled the maturation process in the lab, we then need to measure the effect on the ‘characteristics of the whisky’ as you say Tomasz. This will be a combination of chemical and sensory analysis. For a quick ‘look-see’ we generally use colour as a marker for the extraction of flavour compounds. Chemical analysis is done by gas and liquid chromatography. Sensory analysis will be carried out by a panel of tasters – just like our expert Tasting Panel at the Society.

In this case, rather than creating colourful tasting notes, we ‘measure’ flavour, using panellists’ noses in the same way we would a laboratory instrument. For example, in Quantitative Descriptive Analysis the taster is asked to score the intensity of individual aromas (eg sweet, woody, sulphury, fruity) which builds a flavour profile for each sample.

So yes, we can model and predict the effect of temperature on maturation. But regardless of what these carefully controlled experiments tell us – we also need to consider the single most important determinant – the cask itself. And we don’t need science to tell us that – as all Society members know, every single cask is unique!

I’ll leave you with one particularly interesting observation from the experimental data. The rate of extraction (of colour) does not really take off until you reach average temperatures that are only experienced in Scotland for a few months in the year. Make of that what you will! What it tells me, and of course I say this with tongue firmly in cheek, is that Scotland might not actually be the best place to mature whisky – in terms of economics that is!

Do you have any questions about the whisky making process or what the Society does? Ask Dr Andy Forrester by sending your query by email with your name and member number