Triple distillation in Scotland

Auchentoshan still room

Scotch malt whisky is usually distilled twice in pot stills. There are some exceptions: Auchentoshan and Hazelburn (produced in Springbank distillery) are distilled three times. Benrinnes and Springbank use their own partial triple distillation methods and Mortlach is actually partially quadruple distilled. There have also been some with malt whiskies distilled in Coffey- Stein- or Lomond-stills and recently even a fully quadruple distilled malt spirit from Bruichladdich.

Old Irish pot still at Midleton (wordpress.com)

Triple distillation was and is used extensively in Ireland at least from the late 1800's, probably because of a mixture of malt and grain used in big pot still distillations did not give a sufficiently pure spirit in two simple distillations. In early 1800's a common method in Ireland was to divide the product of the wash distillation into strong and weak low wines and then distill them separatedly into new spirits feints and then re-using the feints from both low wine distillations in the next weak low wines distillation. This is actually modified double distillation, which could have been useful especially if the lower cut point of spirit distillation was to be kept quite high, which in turn would have enabled the production of cleaner and lighter style of spirit. During the 19th century as the Irish pot stills were becoming bigger the simple triple distillation was adopted in several Irish distilleries.

It is a common belief that Scottish Lowland distilleries were also using triple distillation at the time, but actually only four or five of the 31 lowland distilleries toured by Alfred Barnard in 1886 were using some sort of triple distillation. Note that just a few distilleries were producing whisky by only continuous Coffey or Stein stills, the 26 others producing at least some pot still lowland malt whisky. Dundashill produced double, triple and Coffey-still distilled whisky and sold them separatedly for blenders. Clydesdale and Greenock produced only triple distilled whisky as probably did Glentarras, too. Glentarras had one wash still, two spirit stills and one feints still, but there are no spesific descriptions of its distillation method, so it is possible that it was just partially triple distilled. Cameron Bridge produced mainly grain whisky, but also "Pot Still Irish" (grain and malt in pot stills?), "Silent Malt" (malt in Stein still?) and "Flavoured Malt" (malt in pot still?), and it is possible that some of these was/were triple distilled. For example Auchintoshan (now Auchentoshan) was double distilling and Rosebank most probably partially triple distilling in 1886. Hazelburn used triple distillation in Campbeltown, but there are no records of triple distillation in the Highlands or the Speyside at the time.

It is not exactly known, when Auchentoshan turned into triple distilling, nor whether in what extent Rosebank has used double, triple and partial triple distillation regimes during the 1900s. One source (Brian Townsend's Scotch Missed) claims triple distillation was used in Rosebank for decades, but according to Ulf Buxrud and the DCL archives partial triple distillation, much in the lines of Benrinnes, was used in the 20th century. Benrinnes has been using partial triple distillation probably from 1954 and Springbank apparently from the early 1900's. The old Hazelburn distillery was operational from 1837 to 1925. It is not known whether they used triple distillation from the beginning, but the spirit stills were quite unique as they had water jacketed tube condenser systems attached to the neck of the both spirit and feints stills (before the lyne arm) and then after the lyne arm the typical worm condensers of that era. These stills probably had very much reflux and consequently the spirit was probably quite light. The new Hazelburn was distilled first in 1997 at the Springbank distillery with "normal" stills.

Auchentoshan uses a simple triple distillation with a very narrow heart cut in the spirit run (82.5 to 80.0 ABV), which produces very light and aromatic whisky.

The Benrinnes distillation system is described in the picture below. Basically the weak feints from all (wash, feints and spirit still) distillations are redistilled in the low wines still and the first part of that is added to the spirit run. This probably adds to the copper contact for the feints fraction.

In Springbank every fifth wash distillation is double distilled as the other four batches undergo a triple distillation. All the feints are added to the intermediate still. The effect is probably much the same as in the Benrinnes system resulting in more copper contact for the feints.

In Mortlach one wash and spirit still produce simple double distilled malt whisky. The rest of the stills produce about 80% of double distilled spirit and 20% of quadruple distilled whisky. The amount of finished quadruple distilled whisky is probably much less as the latter part of the wash (weak feints) is much weaker in alcohol. The weak feints are distilled three times in a small still called the "Wee Witchie"; the first two distillations are blank runs and only solids are removed in between. The third distillation is fractioned in the normal way and the heart is mixed with the product of the other spirit stills. Because the Wee Witchie is small (7 880 litres compared to 17 000 litre spirit stills 2&3), squat and cooled with worm tubs as the other spirit stills, the copper contact is not substantial, but it is possible that the four distillations might change the properties of the feints fraction in other ways, such as successive heating, which might in turn alter the spirit. It is believed that the meaty aromas often noticed in Mortlach whisky are due to the Wee Witchie and the "Byzantine" distillation system, which has been in use from at least 1971.

Mortlach still room, the Wee Witchie at the back (from whiskymonitor.nl)

REFERENCES AND FURTHER READING:

Barnard A. The whisky distilleries of the United Kingdom. Birlin ltd 1887.

Buxrud U. Rare malts. Quiller Press 2006.

Morewood S. A philosophical and statistical history of the inventions and customs of ancient and modern nations in the manufacture and use of inebriating liquors. Longman 1838.

Townsend B. Scotch missed. Angel's share 2000.

Udo M. The Scottish whisky distilleries. Black&White Publishing 2006.
Weir R. The history of the Distillers Company 1877-1939. Clarendon Press 1995.

Lactic acid bacteria

Lactic acid bacteria (LAB) are a diverse group of bacteria capable of lactic acid production. They are found for example in cheeses, yoghurts or decomposing plants. They are non-respiratory (anaerobic), but tolerate also aeriated environments and can survive high acid (pH 3-6) and high ethanol concentrations. The Lactobacillales can be divided into different genera, such as Lactobacillus, Leuconostoc, Pediococcus, Lactococcus and Streptococcus etc. Of these the Lactobacillus and in lesser extent the Pediococcus are dominant in distillery environment, although many others survive alongside them. The LAB are present in small quantities in the raw materials, especially the grain, but generally the contamination of wort with LAB comes from the distillery environment (pipes, washbacks etc) and therefore the LAB population in whisky distilleries remains quite stable and the dominant strains of LAB are practically unique in any one distillery.

The yeast dominates the early fermentation and LAB starts to grow significantly after about 36-48 hours as the yeast starts to drop out or die. At the start of the fermentation there are usually various types of LAB in the wort, but many of them die out as the ethanol concentration rises. The first LAB to grow are usually heterofermentative ie they metabolise sugars into lactate, acetate and CO2, the most common species being L.fermentum, L.paracasei and L.brevis. The homofermentative LAB, such as L.acidophilus and L.delbrueckii, producing only lactate from sugars appear later after about 70 hours of fermentation.

Microbes in whisky fermentation, MB-stained=dying cells (Priest 2004)

The heterofermenting LAB can also use pentose sugars, which the Saccharomyces cerevisiae can not ferment, so they are not necessarily competitive. The homofermenters use only hexoses and they always reduce the spirit yield a bit, although they can also use the autolysis products of the dying yeast for their metabolism. The usual amounts of LAB at the start of the fermentation (below 10^6 cells/ml) do not affect the spirit yield, but amounts greater than that could cut the yield up to 20%. The usual amount of LAB in the wort are usually 10^4 to 10^5 per millilitre and rise up to 10^9 at the end of a long fermentation.

Growth of lactic acid bacteria in whisky wort (van Beek 2000)

The effect of LAB on the flavour profile of whisky depends on the species and even the strain of the LAB. Also the availability of metabolites via yeast cell death affects the flavour profile. Probably the most important and common effect of LAB is the increase of lactic and acetic acid, which together with sufficient amount of alcohols leads to increased levels of esters. The lower pH also affects the volatility and activity of various aroma compounds during fermentation and distillation.

The yeast cell death allows the LAB to metabolise the autolysis products, for example the cell membranes containing lots of fatty acids. The LAB hydroxylate these fatty acids into gamma- and delta-lactones, especially gammadecalactone and gammadodecalactone, which produce a heavy sweet and fatty aroma also found in tropical fruits (apricot, peach). The use of brewer's yeast in the fermentation leads to faster yeast cell death and subsequently to higher levels of gammalactones with sweet and fatty notes.

The LAB can alter phenolic aromas as they can decarboxylate cinnamic acids to 4-vinyl guaiacol or 4-vinylphenol and further to 4-ethylphenol. Ferulic acid and p-coumaric acid are common cinnamic acids in malted barley and a typical distiller's yeast (DCL M) and most wild yeasts, but not most brewer's yeasts, can decarboxylate them into 4-vinylguaiacols (smoky, spicy, clove). The LAB has the same decarboxylation enzyme, but they can reduce 4-vinylguaiacol further to 4-ethylphenol (guaiacol, barn-yard, band-aid, brettanomyces), which usually softens the smoky aroma. The smoky aromas are dimished especially if the fermentation is allowed to continue longer.

Amounts of guaiacols in whisky fermentation with DCL M+LAB (Van Beek 2000)

	fruity	fatty	green	sweet	sour	sulphury	meaty
L.paracasei	+		+		+
L.plantarum	+		+		-
L.brevis	(-)	+	(-)	++		++	++
L.casei	+	+
L.fermentum	+	+	+
L.acidophilus		+	+
T.delbrueckii (wild yeast)	-	(+)	+	+	-	(-)	+/-

Some effects of LAB and wild yeast on the flavour of new-make spirit (Van beek 2002, Priest 2004, Wilson 2008)

The growth of LAB depends heavily on the cleanliness of the distillery. Most of the LAB from the raw materials die during the malting and mashing and the main source for the LAB is from the pipes and the washbacks. Steel washbacks are easier to clean and probably lead to lower and different LAB colonies in a distillery. Long fermentation times increase the LAB growth, especially after 48 hours. Some distilleries have variable fermentation times, for example shorter during the week and longer over the weekend, which tends to produce slightly different wash profiles. Below is a table about different distillery fermentation practices.

Distillery fermentation times and washback materials (Udo 2006)

Variable fermentation times (usually weekdays/weekends)

REFERENCES AND FURTHER READING:
Booysen C et al. Isolation, identification and changes in the composition of lactic acid bacteria during the malting of two different barley cultivars. Int J Food Microb 2002;76;63-73
Bryce JH et al (ed). Distilled spirits: Production, technology and innovation. Nottingham Univ Press 2008
Simpson KL et al. Characterization of lactobacilli from Scotch malt whisky distilleries and description of L.ferintoshensis. Microb 2001;147;1007-1016
Smit G., et al. Flavour formation of lactic acid bacteria and biochemical flavour profiling of cheese products. FEMS Microb rev 2005;29(3);591-610
Udo M. The Scottish Whisky Distilleries. Black & White 2006
van Beek S, Priest FG. Evolution of the lactic acid bacterial community during whisky fermentation. Appl Microb 2002;68(1);297-305
van Beek S, Priest FG. Decarboxylation of substituted cinnamic aceds by lactic acid bacteria isolated during malt whisky fermentation. Appl Envir microb 2000;66(12);5322-5328
Walker GM, Hughes PS (ed). Distilled spirits, new horizons: energy, environment and enlightenment. Nottingham Univ Press, 2010
Wilson NR. The effect of lactic acid bacteria on congener composition and sensory characteristics of Scotch malt whisky. Thesis Heriot-Watt Univ 2008.