Why do some Scotch whiskys have a sulfur taste?
In the past, some of this sulfur was due use of a sulfur candle; the inside of the ex-sherry casks could be prone to microbial contamination, and so sulfur candles were burned inside them, with the sulfur acting as a preservative.The idea was that the amount added was enough to prevent microbial growth, while not enough to significantly affect the taste. When did this problem really become prominent? Apparently the 1990’s.
Calling it ‘singly the biggest screw-up in the whisky industry in the past quarter of a century’, whisky writer Jim Murray is unequivocal about the source of sulphur notes in whisky, the result, he says, of a very modern error, introduced in the 1990s, when with a change of law Spanish producers were no longer allowed to export their Sherry in anything other than bottle. Empty casks – destined for the whisky industry, sat waiting during summer months – were suddenly vulnerable to spoiling, prompting the ramping up of the age-old practice of fumigating their insides by burning sulphur candles.
– What’s wrong with sulphur in whisky? Dave Waddell, 9/25/15, Scotchwhisky.com
The Scotch whisky industry no longers follows this practice.
However, other whiskys, past and present, could have a subtle sulfur taste for different reasons. Sulfur containing compounds, certain amino acids, naturally exist in barley. So when the barley is fermented, a small amount of various sulfur containing compounds may form, including hydrogen sulphide, methyl disulphide and thiols.
Whisky makers control their process to reduce the amount of these compounds. They do this selecting the correct grains and yeast, fermenting for the right amount of time, and cutting the heads and tails of their product to remove most sulfur-rich compounds. Yet let’s note that deciding where to cut is always a trade-off: A distiller might want to include a bit more feints because this would provide some of the heavier esters (flavorful compounds) although this might add more sulfur compounds.
Further reduction occurs while whisky ages in charred oak barrels. Some of these compounds evaporate, and others are chemically changed into more desirable compounds.
During distillation in a pot still the distillate touches copper metal; a copper containing compound is then made, which is removed from the distillate. When using a continuous still, there’s often a chamber at the top of the analyser that holds some copper, which catalyzes the sulfur compounds into other compounds.
Steve Porter writes “Steve Porter Copper removes sulphur that is produced by yeast. The sulfer molecules become hydrogen sulfide and then attach to the walls of the still becoming copper sulfate as it dries. If the still is stainless the sulfates/sulfides remain in the distillate. Here is a short video of a copper sulfate solution collected from my still after a cleaning run of my 50 gallon all copper pot still”
In any case, having the right amount of sulfur can add a sense of weight & flavor, sometimes called umami notes. Some folks like this. Certain distilleries are famous for this e.g. Benrinnes, Craigellachie, Mortlach, Dailuaine.
BTW, a question for our readers: Do you think that any old-school, pot-still, bootleg mountain moonshine had umami or sulfur flavors? Some used lead-solder, car-radiator, wormtub condensers. If you have any notes on this please drop me a line!
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