We had a fantastic visit to the Diageo copper works in Alloa the other day. This facility is dedicated to ensuring the copper stills at all of Diageo’s European distilleries are kept in good working order.

We learned that it takes 4 years of apprentice time to qualify as a coppersmith.

There was a point in time when copper stills were made by the hot rivet method as this photo of an old still section shows.

Today, the 6 mm copper sheeting is oxy-acetylene welded with copper rod. At the time of welding, two welders work in tandem. One person welds the top side of the seam while his co-worker does the underside. Take this bit of trivia seriously. If a stillmaker tries to tell you that he cannot offer you 6 mm copper because it is too light to weld, you are dealing with the wrong supplier. Find a stillmaker who can do oxy-acetylene welding on 6 mm copper.

We also learned that copper is essential in removing sulfides from the material being distilled. A visit to the Scotch Whisky Research Institute has confirmed this. What’s more, we learned that people who are using a stainless steel pot and a copper column will make OK spirits, but to make exceptional spirits, a full copper system is needed. Sadly, I am seeing a lot of suppliers providing craft distillers with stainless pots and copper columns or sacrificial copper in the column. Why would a person opt for stainless so they can make just OK spirits. If you are getting into the craft business, why not aim to make the best possible product ?

Here are 3 copper still destined for Ireland. Why 3 you ask? That’s because Irish Whisky is triple pot distilled.

Here is a shell-in-tube condenser. Diageo has 9 distilleries that use the worm tub type condensers. All their other operations use shell in tube. We learned that the lesser surface area of a worm tub will give a distillate that is heavier and potentially with more sulfur notes than shell in tube.

And lastly – what happens when you weld copper? Yep – it gets hot all over because copper is a heat conductor. This heat anneals the grain structure. We learned that soft copper will be prone to erosion from stripping runs. At Diageo copper, all copper sections are hand hammered to “work harden” the copper grain structure. This prolongs the life of the still. If you are ordering a copper pot, ask the supplier if they have hammered the surfaces to harden the copper structure. If they look perplexed at that question, you are dealing with the wrong supplier.

Take caution if you are shopping for stills. There is a lot more to the structure of the metal than I ever imagined.