As a malt producer it is important to understand the details of the distilling process in order to deliver the best suitable quality. Here we look at single malt distilling, as the preparation of the wort for grain distilling is somewhat more complex.
Traditional single malt whisky production
In Scotland it’s obvious that local ingredients are responsible for the way whisky was and still is made. Local barley (a grain that can survive the difficult growing conditions in Scotland), local peat (the fuel for heating and kilning) and the alembic or pot stills (a distilling device they borrowed from their Irish neighbours).
The classic wort production uses specially modified distilling malt, with a low protein level of 10% maximum. There are two reasons: a lower protein level delivers higher extract, and proteins are contaminating the burner coils in the stills. Crusted malt is mixed with hot water entering the mash tun, to achieve a mashing temperature of 63°C (145°F). This is the ideal maximum activity of ß-amylasis. A rake is mixing the mash and after half an hour you can start draining by decantation. To wash out the rest extract, hot water is added in 3 sparges, the last one at 90°C (194°F). The wort is cooled down to below 30°C (86°F) and collected in the wash tun for fermentation.
The first (main) wort runs off at 63°C (145°F) and the wort is not cooked as in the beer process, but only cooled down. Therefore amylase activity continues in the wash tun (fermentation). During a couple of days a wash of aproximately 10% to 15% alcohol is obtained. Thanks to the still limited activity of the amylase enzymes, almost all amylose and amylo-pectine has been converted to fermentable sugars.
The yeast used for fermentation is often a mix of a specific own yeast and brewing or even baking yeast. As pictured, the concentration of alcohol happens in minimal 2 distillations. The main goal is to reduce volume and contrate alcohol. The heavy boiling gets beside alcohol and water also heavy fusel oils.
| Duration 4 – 7 h. | Wash tun | Low wines |
| Alcohol concentration | 10% | 26% |
| Volume reduction | 100% | 37% |
In the next step purification of the low wines happens in the spirit still. According to British law, all piping and pot stills have to be padlocked. This makes it impossible to check organoleptic control on flavours and alcohol by the stillmen. Therefore a lot of measuring is happening in the spirit safe, because it’s not possible to taste.
There is only a certain window in the distilling process suitable for further spirit collection (the middle cut). The first condensate in the beginning of the distillation (foreshots) contain a lot of aldehydes. The middle cut is what the distiller wants as crude spirit. At the end of the distillation, the fusel oils evaporate. Both fusel oils and foreshots are lead back to the low wines receiver in order to re-process and recuperate the alcohol.
| Duration 3 h. (middle cut) | Low wines | Raw spirit |
| Alcohol concentration | 26% | 67,5% |
| Volume reduction | 37% | 14% |
The distillation of the middle cut must happen very carefully and slowly in order not to transfer the fusel oils. After distillation is finished, the raw spirit will be maturing in wooden cask. To called it whisky, the spirit has to stay in the barrel for at least 3 years. The barrel is responsible for the colour and certain aroma’s .
Sherry and bourbon casks are very popular for maturation. The amount of peat used during kilning, the shape of the stills, the casks and the phenol content define the final whisky. Low peated whiskies should have around 0-3 ppm phenol, while high peated whiskies can go up to 30 ppm phenol and above.
Distillation of alcohol can be problematic, certainly when working with copper distillation devices. In the past, certain barleys could form dangerous cyanides. Once this was discovered forty years ago, the whisky industry changed to malt from barley varieties that can be used safely. Best known are Laureate, Concerto and Odyssey – luckily also excellent brewing varieties. That is why our malts are suitable for both brewing and distilling.
Crafted alcohol production
Craft distillers usually have a more varied equipment, depending on the spirit. The installations are small and often suitable for making clean spirits like gin and wodka, and more aromatic spirits like jenever and whisky. A lot of those craftsmen also appreciate the possibilities of speciality malts with their typical taste and aromas.
With a column still it’s possible to make almost pure alcohol (96%), even in one step and/or in a continuously process. This is not possible with a pot still. That’s a batch related process where 70% can be achieved in the final spirit. Followers of the pot still claim to have more aromatic spirits, and believe the choice of malt types could be more explicit. In general it does not matter if one uses pot still or column stills, it is the distiller who has to make the cuts.