![]() By definition, the style “London Dry Gin” begins the process of distillation with a neutral spirit that has already been refined and had many of the impurities, including sulphites removed. Stainless steel is therefore ideal for production of stills to be used for distillation processes where removal of sulphites have already been carried out, such as the production of London Dry styles of gin. Stainless steel doesn’t react in the same way, but has similar properties with regard to malleability and heat conduction, but also other advantages when it comes to cost, strength and durability. Pure copper plays a critical role in “cleaning up” the spirit, and the superiority over brass, aluminium, iron and stainless steel for the initial stages of distillation are evident in the final product. This patina can then be washed off during routine cleaning cycles. This copper sulphate adheres to the internal surface of the copper in the still to form a patina, or thin layer of the compound. The majority of this reaction happens in the “vapour” part of the still, where the spirit reaches its highest temperature before being condensed. The resulting compounds are insoluble and so precipitate out to form copper sulphate, sacrificing a tiny amount of copper from the still in the process. Hydrogen sulphide is capable of reacting with many metal ions, one of which is copper. ![]() Sulphites will initially react with hydrogen ions within the liquid to produce hydrogen-sulphide which gives the unpleasant “rotten egg” odour and is toxic and highly flammable. This is where the chemical properties of copper are critical. Even tiny concentrations are detectable to human senses, rendering the spirit unpleasant. Sulphites are a different story and humans are particularly sensitive to their presence. This is of course assuming the distillers know what they are doing! Tiny amounts may sometimes remain in the final product, but in quantities too minute to be harmful to humans. Methanol and acetone can easily be removed during the distillation process as their boiling points are lower than ethanol and as such they are the first compounds to be fractionated off during distillation, and removed with the first cuts. ![]() However, some compounds are undesirable and occasionally toxic, such as acetone, methanol and of course, sulphites. Many of these compounds are harmless and indeed desirable, contributing to the flavour and complexity of the spirit. Additionally, many yeast die and break open during this high stress stage of fermentation, further increasing the molecular diversity of the mix. When the oxygen runs out, their metabolism flips into survival mode, at which time they start breaking down any remaining sugars to produce ethanol along with a huge array of other compounds. During the fermentation process, yeast initially grow in large numbers, utilising some of the sugars in the wash, along with any spare oxygen. Through a fortuitous quirk in yeast evolution, yeast produces alcohol when starved of oxygen (unlike humans that produce lactic acid, and plants that pretty much couldn’t care less). Yeast is the key player in all alcohol production.
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