DISTILLATION AT MORTLACH EXPLAINED

 THAT MAGIC FIGURE OF 2.81

DISTILLATION AT MORTLACH

Mortlach was founded in 1823 as the first legal distillery in Speyside’s Dufftown. Mortlach is said to defy what Speyside whiskies are known for. It is thick, rich, muscular, meaty, umami-led and savoury and known as the ‘Beast of Dufftown’. The character comes from its 2.81 distillation process which started in 1897 and the process is still in use at the distillery today. 

MORTLACH 2.81 DISTILLATION EXPLAINED

THE WEE WILLIE AT THE OTHER END

The 2.81 distillation process was put in place in 1896. Every single part of the production process at the distillery is tailored and calibrated to create that robust, savoury, muscular style. From the short fermentation times of 53 to 58 hours through to the still house and the condensers, Mortlach uses worm tub condensers which are only found in fourteen distilleries across Scotland.

Mortlach distillery has 6 stills; 3 wash stills and 3 spirit stills and what sets them apart is that all their stills are of different shapes and sizes and they all work pretty much independently from one another. They don’t work in perfect pairs but create three different spirit characters from the three spirit stills which are then blended to create the house style. It’s akin to having three distilleries at the one still house. Production began in 1897 using specific processes.

The first of these is the pairing of wash still 3 and spirit still 3 to create a malty distillate. Wash stills 1 and 2 work as a pair, which is unusual. They then take everything that has run through and split it into half, the heads and the tails. The first half from wash stills 1 and 2, the low wines the lighter half, are run through spirit still number 2 which creates a lighter floral distillate.

The heavier half of wash stills 1 and 2 is run through spirit still number 2 once but no cuts are taken. Everything that has run through is run through a second time but with the tails from wash stills 1 and 2. The heavier half and the richer half get richer and more viscous.

If spirit still number 1 is small, and its filled high, then it’s a bit of a copper contact. Taking it around twice is not really cleaning it to that same effect, so no cuts are taken. Everything that has gone around that second time is run through a third time with the set of heads from wash stills 1 and 2 because, by this point, it has become way too thick and way too viscous. A spirit cut is taken from that.

A spirit cut is taken from spirit still number 1 from every third run. Mortlach use worm tub condensers and the water is cold at 10 degrees, which means as soon as that vapour hits the copper, it turns back into liquid. So when the spirit is in liquid form, the copper cannot do its work, so every part of the production process is calibrated to create this character, and this has been calculated to be 2.81.

Thanks to the mind-boggling distillation process developed at Mortlach in 1897, they created something in between double distillation and triple distillation, and it’s called 2.81 distillation.  There are a number of sources online that have described the process, some of them better than others, but overall even after a few hours research, you might still find yourself confused. Some claim that the figure is 2.70.

Mortlach has six copper pot stills, three of which are wash stills, the No.1 and No.2 wash stills are the smallest at 7,000 litres, and the No.3 wash still is much larger at 16,000 litres.  Of the remaining three stills, it will be best to start with the most simple of the three.  Spirit still No.3 is fed by wash still No.3 in a conventional manner, i.e. the wash still produces low wines (low strength spirit usually between 21-25% ABV) and this spirit stream enters spirit still No.3 where cuts are made so as the foreshots and feints are recirculated into the still and the heart can enter the worm tubs. Things start to get a bit more complex now.

Wash stills No.1 and No.2 each have two spirit streams, 80% of the wash from both of these wash stills is channelled to the No.2 spirit still, this 80% is known as the heads, this is where the lighter chemical compounds and the majority of the ethanol is present. Once again cuts are made, the foreshots and feints are recycled back into the spirit still and the heart makes its way to the worm tubs.

The third of the spirit stills, the ‘Wee Witchie’, is the smallest of the three. The

Wee Witchie is integral to the Mortlach distillery when it comes to producing the distinct weightiness of Mortlach, you could even say that it’s the Wee Witchie that makes Mortlach the ‘Beast of Dufftown’.  From the No.1 and No.2 wash stills 20% of the wash known as the tails are channelled into the No.1 spirit still (the Wee Witchie), these tails are low in strength, contain a lot of water and some of the chemical compounds produced in the fermentation phase, one of which is sulphur and it’s the sulphur that gives Mortlach it’s weightiness. Three distillations of the tails are carried out in the Wee Witchie, two of which are blank runs meaning that no cuts are made, and all of the distillate reenters the still; it is only on the third run that cuts are made and the heart makes its way to the worm tubs.  What this triple distillation in the Wee Witchie does is limit the amount of sulphur that can be removed from the distillate so that more sulphur is present in the new make Mortlach than you would usually find in most whiskies.  When sulphur in the distillate reacts with the copper of the pot still it forms copper sulphate which essentially remains glued to the inner wall of the pot still meaning that there is less sulphur in the new make spirit as a result, but in the case of Mortlach the inner wall of the Wee Witchie becomes so saturated with copper sulphate that a lot of the sulphur can no longer bind to the copper and subsequently goes on its way to the worm tubs.

The worm tubs also play a crucial role in producing a more sulphurous spirit, there are only a handful of distilleries that continue to use worm tubs as their method of condensing.  The worm tubs are metal tubes, usually copper which are coiled around many times, these ‘worms’ sit inside ‘tubs’ of cold water, hence the name ‘worm tubs’.  Once the distillate vapour enters the worms it condenses and the liquid new make spirit comes out the other end.  Most distilleries today use ‘shell and tube’ condensers which are made up of many very thin copper tubes which are contained within a metal shell where they’re surrounded by circulating cold water.  The shell and tube condensers significantly increase the spirit’s contact with copper, thus removing even more sulphur.  By using worm tubs, the surface area of the copper that comes into contact with the spirit is greatly reduced meaning more sulphur remains in the spirit, this is another factor that contributes to Mortlach’s weightiness.

Mortlach 2.81 Distillation Calculation                               

Stage 1: Calculating the ratio of double and quadruple distilled spirit                  Percentage of x4 distilled spirit from spirit still No.1 (Wee Witchie) = 33.9622641509434% (33.9623%)                                                      Percentage of x2 distilled spirit from spirit still No.2 = 32.0754716981132% (32.0755%)                                                                                      Percentage of x2 distilled spirit from spirit still No.3 = 33.9622641509434% (33.9623%)                                                                                      Percentage of spirit that is x4 distilled = 33.9622641509% (33.9623%)    Percentage of spirit that is x2 distilled = 66.0377358491% (66.0377%)    2/100×33.96226 = 0.67925                                                      2/100×32.07547 = 0.64151                                                                  4/100×33.96226 = 1.35849

Stage 2: Adding the ratios together to give the distillation figure (the simple way of doing this gives a figure of 2.7 which is often what some people claim as being Mortlach’s number of distillations).

0.67925+0.64151+1.35849 = 2.67925 (The 2.7 figure that some people often claim is the ‘true’ distillation ratio of Mortlach).

Stage 3: Incorporating a correction factor for the distillation process, which when added to the figure of 2.7 gives the stated figure of 2.81     

1.35849-1.32076 x 3.396226 = 0.12814                                             2.67925+0.12814 = 2.80739 (2.81)