Monday 28 August 2017

Whisk(e)y Distillation process

Pot distillation versus Column distillation

The first of questions that come up about whisky distillation is regarding pot distillation versus column distillation. Pot distillation (figure 1 a) is where the beer mash is heated in kettle like large copper pots and column distillation (figure 1 b) is relatively new, and more efficient way of mass producing alcohol. Bourbon whiskies, vodka and gin are produced in column stills. While there are several blog posts about the difference of these two distillation processes [Ref 1, Ref 2 ], in this post I am more focused on its effect on the taste of the whisky.


 
                   Figure 1 (a) pot still at Auchentoshan               (b) A Column still used to make Gin


Grain Whiskies vs Malt whiskies

No two single malts will taste the same. However to conquer international markets scotch whiskies had to be consistent. This consistency was achieved through blending. Grain whiskies came in to play to act as ingredients for blended whiskies.
While malt whiskies are made from a beer that is made of malted barley, grain whiskies are made of either barley (unmalted), wheat, corn or rye.
Jamesons, the popular Irish whiskey, is a single distillery blend of malt whiskies, corn and barley grain whiskies.
In a typical blended scotch whisky the ratio between malt to grain is approximately 30/70.
As of 2015, while there are nearly 109 malt distilleries there are just 7 grain distilleries in Scotland. However, grain whisky production is much higher than malt whisky production [Ref 3].
Column stills are used to produce grain  whiskies, and are purified to a higher degree than malt whiskies.

Why use copper for stills?

A by-product of the fermentation process produces Hydrogen sulphide, which may cause  a bitterness in the whisky. When copper stills are used, these sulphur components react with the copper and form copper sulphate, which gets deposited in the still. These can be washed away after the distillation process. Hence, the spirit distilled in copper stills will have less sulphur components. In the figure 2 you can see the result of a copper still wash, with the top layer containing a residual copper sulphate. 


Figure 2: The copper sulphate that residues on the copper still. 


References

[1] serious eats blog post
[2] Whiskey wash post
[3] whisky invest post
[4] Whisky.com post

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