Cotswolds may be a relatively new distillery, but they make their English whisky the old-fashioned way in copper stills controlled by man rather than machine, carefully following procedures put in place by Harry Coburn, former general manager of Bowmore, and Jim Swan, one of the world's greatest whisky-making legends.
It starts with Cotswolds' barley
Only locally sourced organic barley is used, a variety called Odyssey grown in the Cotswolds on the Blenheim Palace Estate and a farm near Burford. The barley is malted at Warminster, Britain's oldest working maltings in operation since 1855, still malting barley the traditional way.
Trucks transport the malted barley from Warminster to feed the 17½ tonne silos behind the distillery. An overhead conveyor moves the barley to a weight calibrated hopper above the roller mill, filled to 525kg for each mash.
The mill is set to produce a typical single malt whisky grind with a grist comprising 20% coarse (thick outer shell of the malt), 70% middles/grit/hearts (texture between husks and flour) and 10% flour. Samples of grist are taken twice a week and the mill recalibrated if necessary, to maintain the desired 10:70:10 consistency which is crucial for maximum extraction of fermentable sugars during the next process: mashing.
The grist from the roller mill is fed into the mash tun along with water added via a mash mixer - just over 2,100 litres of water at 63.5°C to the just over 500 kilos of malt, so a 4:1 ratio. The temperature is crucial to gelatinise the starches in the barley and reactivate the grain's enzymes. Too hot and the enzymes would be cooked; too cold and the starch won't gelatinise, in which case the enzymes can't work. Unlike other distilleries that have sensors in the line that automatically inject cold water to adjust the temperature, at Cotswold they prefer to do it manually, gauging the ambient conditions every morning and adjusting accordingly to hit the desired 63.5°C.
The water used may be Severn Trent "tap water" but it undergoes a three-step purification process: charcoal filter, water softener and reverse osmosis to ensure consistent neutrality.
It takes some 30 minutes to fill the mashtun, then the grist and water mix are stirred for 5 minutes before being left to rest for an hour. This resting period allows the course grist to settle and form a grain bed and gives enzymes time to start breaking down sugars into manageable units for the yeast in the next phase (fermentation).
After the hour of settling they start running off to the washback, along the way passing through a heat exchanger to bring the temperature down from 63.5°C to the perfect fermentation temperature of 20°C. After an hour of running off, the level in the mashtun falls and starts to expose the grain bed. At this point 850 litres of sparge water at 78°C is showered into the mashtun. This second water helps rinse the residual sugars out of the grain and is combined with the first water to fill one the of the eight washback fermenters with 2,600 litres of wash.
A third water at 88°C is then pumped into the mashtun to capture any remaining sugars in the malt. This last water is transferred back to a hot liquor tank and saved to become part of the first water for the next brew. Once the third water has drained out the mashtun the draft (spent grain) is removed to end up a tasty meal for local livestock.
The yeast is pitched very early at Cotwolds, after about 10 minutes of running into the fermenter when the liquid is a mere foot deep (30cm). This gives the yeast a head start on bacteria and other unwanted microorganisms. Early pitching and the use of a blend of whisky distilling yeasts (Anchor DY502 and Fermentis NET1) is due to the influence of Jim Swan, the legendary whisky distiller.
It takes some three hours after the start of runoff from the mashtun to fill the washback, at which point a knob of butter is thrown in to act as a natural anti-foamer. This is preferable to a switcher blade to prevent bubbles from rising too high as keeping switcher blades clean is problematic so risking reintroducing bacteria to further brews. Jim was apparently quite a proponent of butter but was very against silicon anti-foam as he felt this would clog the surface of the copper stills, so harming what distillers call the "copper conversation with the spirit vapour".
Fermentation lasts just shy of four days, so if the fermenter is filled by 11am on a Monday then it will be ready to be pumped into Mary, the wash still to start distilling by 8am on Friday.
Cotswolds has a pair of traditional copper pot stills, a wash still called Mary and a spirits still called Janis. Mary is named after the song Proud Mary by Creedence Clearwater Revival due to the "big wheels keep on turning" lyrics. Like the wheels of Proud Mary steamboat, the pot still just keeps on chugging along all day long. Janis is named after Janis Joplin due to her hit, (Take A Little) Piece Of My Heart referencing the 'hearts' of the spirit run produced by the still.
Wash still called Mary in the foreground with spirits still called Janis behind
Due to the use of a heat exchanger to recover heat from the pot ale from previous distillations, the wash enters Mary at around 60°C so it only has to rise into the 80s before it starts to boil and the spirit starts to run via a shell and tube condenser into the spirits safe. Made specifically for the distillery, the spirits safe may be brand new but it looks vintage, a reference to the distillery making whisky using tradition techniques and equipment.
The low wines start running at a little over 45% alc./vol. and Mary is run until the strength falls to about 2% alc./vol.. Many Scottish distillers continue down to 1% but the folk at Cotswolds say this can become uneconomic due to the energy used to gain so little alcohol and more importantly, in their quest to produce a cleaner fruity spirit they want to avoid the heavier compounds that result from running beyond 2% alc./vol..
Mary runs for about five-and-a-half hours to produce roughly 800 litres of low wines at around 23-25% alc./vol. from the original charge of 2,600 litres at about 8% alc./vol..
The low wines from Mary are moved across into Janis with the foreshots and faints (heads and tails) from the previous run. The combination of low wines, foreshots and faints comprise a 1,400 litre charge at around 32% alc./vol.. They don't pre-heat the low wine so Janis starts about 20°C with the foreshots starting to run into the spirit safe after about 25 minutes. The foreshots run for just 7 minutes before the cut to heart spirit is made. Jim was a proponent of the short 7 minute foreshot cut to capture more esters
The switch to hearts is at about 75.5% alc./vol. and this runs at about 100 litres an hour for about two-and-a-half hours to yield 250 litres at about 75% alc./vol.. This is a little higher than traditional Scotch which tends to be 67-71% alc./vol. but lower than triple distilled Irish whisky which can be as high as 82% alc./vol.. Nick Franchino, Cotswolds' head distiller, says, "we've got more of the body of the typical Scotch single malt and yet we've got the fruitiness and lightness of the Irish as well, so it's kind of the best of both worlds having that kind of ABV."
The cut to faint is at 69% alc./vol., also very high in the quest for a fruity lighter whiskey. The faints are run down to 2% before the still is turned off. The foreshots and faints combined (600 litres of 38-39% alc./vol.) are recycled and added to the next batch of low wines to charge Mary.
Cotswolds use a variety of casks to include "some exotics" such as rum, port and madeira casks but their core three cask types are bourbon, sherry and most importantly, STR a Jim Swan development and sherry casks. These three core type of cask account for some 99% of ageing stock.
Bourbon barrels sourced straight from Kentucky comprise about 40% of the inventory with sherry casks representing some 20% and STR casks 40%. The STRs are fundamental to Cotswolds and Jim Swan's method of making whisky. STR stands for shaved, toasted and re-charred. They are ex-red wine American oak casks that have been shaved, toasted and then re-charred at a Portuguese cooperage. The shaving helps remove botrytis from the wine. If the casks were toasted/charred without first shaving off a layer of wine-soaked oak then the casks would produce acrid flavours in the whisky. Burnt grape juice is not desirable. Toasting allows deeper heat penetration into the wood to help caramelise sugars and breakdown the lignin compounds. Charring provides a very active charcoal surface to help remove impurities, but it also cracks the surface of the wood so allow the spirit to flow in and out of the toasted layers. Hence STRs are very active casks that impart fruity spicy sugared notes to a whisky, important for young distilleries such as Cotswolds who want to all people to appreciate their whisky without having to wait for a decade or more.
It worth remembering that age and maturity are not the same thing. Age is just a number while maturity is about character and levels of interaction with the oak. Nick says, "STR casks allow a great deal of mature character to ally with our fruity clean spirit that doesn't need a huge amount of time to oxidize and in the cask and you get a very balanced very mature whisky at a surprisingly young age."
Cotswold's flagship whisky is a three-year-old matured in a combination of 70% STR casks and 30% ex-bourbon barrels. These two casks are blended at cask-strength (they are casked at 63.5% alc./vol.) and then diluted to 50% alc./vol. before re-casking for a final three months maturation. "We feel that marriage definitely helps bring everything together just creates a much more harmonious blend", says Nick.
Cotswold has two bottling lines in their bottling hall, dedicate one to whisky and the other to gin. Both lines are very much hand-operated with a team of five pretty much flat out. Importantly, all the gin and whisky produced at Cotswolds is bottled on site.