The science of alcohol
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The science of alcohol

4 Exploring a working distillery

The Cotswold Distillery located in the Cotswold village of Shipston-on-Stour has been producing gin and whisky commercially on a small scale since 2014 using the process of distillation (Figure 3).

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Figure 3 The Cotswold Distillery, Shipston-on-Stour

In the following video, distiller Sarah MacLellan from the Cotswold Distillery explains the distilling process used to produce their unique gin.

Download this video clip.Video player: soa_1_w6_s4_vid_distilling.mp4
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Here at the distillery, we make a London dry gin. It's a very basic product to make, so we use 96% ethanol and we use water. This is put into our still here, and it is diluted to 60% when it goes in the still. In here, we put our botanicals. So the night before we are due to do the distillation, we put in our three main botanicals. So we put in our juniper, our coriander seed, and our Angelica root. This is then left to macerate overnight. In the morning when the first distiller comes in, we then put in our six botanicals, which is our Bay leaf, cardamom, black peppercorn, lime, pink grapefruit, and our lavender that we use. We then turn the stirrer on in the morning, which then macerates everything together. We then turn the steam on, relieving any pressure from the bottom as we do so. We then wait for about 30 minutes for any distillate to come through. So this still is actually a steam jacketed still. So at the bottom, you can see this stainless steel jacket. This is filled with steam which heats the still very evenly. Once this does come to a temperature of around about about 80 degrees, the vapour inside will then go up the top of the onion. It will then pass along the top there, bypassing this column here, because we don't actually use this for the distillation. The vapour will then travel around the back into the top of our condenser. They can see the dials there. You'll see the temperature rise as the distillate comes through. It'll then pass down through the condenser, passing through lots of pipes filled with very cold water. That will then turn the vapour back into liquid, which you can see in this vat here. So as the distillate comes out of the spout here, it is collected into three different tanks. These three different tanks will actually collect different portions of our distillate. So by that, I mean at different times of the run, different flavours will actually come through. So at the very first part of the distillation, we get a portion called our head's cut. And our head's cut is very stringent tasting, so there's a lot of very kind of sharp flavours in there, things that we won't want in our gin. So that is collected in this tank down here. Then comes our most important part of the cup, which is our heart's portion. So our heart's portion is collected in the main tank here. Once we collect the whole of our heart's cup, it is left to rest in the IBC over there for about five days. This is just to let all of the flavours distribute evenly, all the oils, all the acids will find their own place, basically. We equate it to making a curry at home, actually. So if you leave a curry in the fridge for three or four days, it tastes a lot better than when you first make it. The last portion of our distillate to come through is our tail's cup. So that is collected in the tank over here. And that is similar to the head's cup in that it doesn't taste very nice. It's astringent. It's actually more dank and woody than the head's cup. So that's the reason that we don't really want those flavours in our main portion, our main gin. So now that our gin has rested for five days, we dilute it down to 46% and it's bottled. So we do all of our bottling on-site. It is then packaged up and shipped off to stores all over the country and around the world.
End transcript
Interactive feature not available in single page view (see it in standard view).
  • Looking back to our laboratory-scale distillation, can you make a list of the similarities between the two processes, despite their obvious differences in scale?

  • The basic principle of distillation remains the same, whether the distillation is occurring on a laboratory or on a commercial scale. At a temperature corresponding to the boiling point of ethanol (78 °C) the distillate is collected for conversion into the final gin product. A similar apparatus is used for the distillation, for example a water-cooled condenser to condense the vapour back into the liquid phase again.

The process of gin distillation is actually far simpler than you may think and, although different distilleries will have different production methods for their own specific gins, the process starts off in the same way.

Gin always starts from a blank canvas – a completely flavourless base spirit, typically around 96% ABV in strength. This is known as neutral grain spirit.

Different distilleries will distil this base spirit in the presence of a closely guarded recipe of botanicals to produce their own unique products.

Typically, distillation will occur within a copper still (Figure 4). The copper itself actually plays a number of important roles in the distillation process. The copper is an excellent conductor of heat and it disperses the heat evenly over the surface of the still, allowing the distillation process to be very efficient. But the copper is also thought to strip out any volatile sulfuric compounds which are produced as the gin distils, a process which removes any unwanted flavours and aromas from the final product.

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Figure 4 The Cotswold Distillery’s copper still

So, during the distillation process, with this ability of copper in mind, the still is only filled to three-quarters capacity to ensure that there is sufficient space for the volatile vapours to have plenty of contact with the copper during distillation. The base botanicals are then added – the all-important juniper berries, coriander seed and angelica root – and these macerate (soften) for fifteen hours overnight. It is important that the botanicals are not ‘cooked’ and are instead allowed to infuse into the neutral grain spirit. The following morning the remainder of the botanicals are added.

You will now learn about how unique flavours and aromas are incorporated into specific gins.


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