Malting in 1660s

Just found a nice article about malting barley (or bere) by Sir Robert Moray, probably written between 1660-1673 and published in 1739 as a part of The Memoirs of the Royal Society (ed. Mr Baddam). I will try to find something more recent to blog on later...

Yeasts: pedigree and properties

Compressed Mauri Pinnacle yeast (friends-of-islay.dk)

Yeasts used in beverage production mostly belong to the genus Saccharomyces. There are various species of Saccharomyces, including S.bayanus, S.cariocanus, S.cerevisiae, S.eubayanus, S.kudriavzevii, S.mikitae, S.paradoxus, S.pastorianus and in some sources S.uvarum, which is usually considered as a subspecies of S.bayanus. The nomenclature and classification of species changes almost daily and therefore is not always uniform in literature. The species can be further classified into different strains and there are currently thousands of different strains of S.cerevisiae alone. Hybridization is common between the domesticated yeasts used in alcohol production. The yeasts used in whisky industry are mostly S.cerevisiae although various secondary species have been used with it. Baker's yeast is usually S.cerevisiae, lager yeast is S.pastorianus, ale yeasts include S.cerevisiae and apparently some S.bayanus strains, rum ferments primarily on S.cerevisiae and Schizosaccharomyces (with various wild yeasts) and wine industry use mostly S.cerevisiae and/or S.bayanus together with various wild yeasts (for example Kloeckera, Saccharomycodes, Schizosaccharomyces, Hansenula, Candida, Pichia and Torulopsis).

The simple Saccharomyces yeast is a single-cell fungus, containing 16 different chromosomes and because its genome is diploid, there are 32 chromosomes containing the genome (DNA). It can reproduce by budding (producing a copy of genome and cell organs and dividing into two) or mating by spores. During the evolution of yeasts used in beverage production non- or low-spore-producing yeasts became selected, because consistency of the fermentation was preferred. Therefore the strains used in beverage industry reproduce almost exclusively by budding and therefore their genomes change mostly by spontaneos mutations and rarely by mating/breeding. In addition some yeasts produced polyploid (multiple choromosome sets) or aneuploid (multiple single choromosome or parts of it) genomes, which further improved the consistency as there are more than two copies of one chromosome in case of a harmful mutation(s) and less fertile spore production. The extra chromosomes will further split and/or integrate with the other chromosomes. Put simply: it's complicated. For example the species S.pastorianus (formerly called S.carlsbergensis, S.uvarum or S.cerevisiae var Hansen, etc) widely used in lager brewing was probably formed by hybridization of an ale yeast S.cerevisiae and a wild yeast S.eubayanus and by further mixing genetic material (parts of chromosomes) with S.bayanus, which itself is a hybrid of S.cerevisiae, S.eubayanus and S.uvarum (which is also a strain of S.bayanus species). Because of the complex choromosome structure and the restricted reproduction abilities of domesticated yeasts, systematic and predictable breeding of yeasts is very hard even with the modern genetic engineering techniques.

Proposed development of S.pastorianus and hybrids of S.bayanus (Libkind et el 2011)

Practical classification of yeast is done by its purpose (baking, ale/lager brewing, distilling) and it is common to name strains after the lab which produces it, followed by a number; for example WH301 or WL001. Various yeast labs sell probably the same (or very very similar) yeast by a different name. The yeast strains used in beverage industry can be classified further by their abilities to ferment. Important properties of an alcohol producing yeast are flocculation, attenuation, sugar utilization, ability to work in high sugar concentrations (high gravity brewing), tolerance of alcohol, temperature and various killer factors and whether they are top or bottom croppers.

Lager flocculation

Flocculation is the yeasts' ability to clump together; ale yeast flocculates on the top of the fermentation and lager yeast onto the bottom. High flocculators clump early (about 3-5 days) in the fermentation, which might lead to low attenuation, ie part of the sugars are not metabolized to alcohol. Whisky distillers usually prefer low flocculators, because flocculated yeast is more likely to stick to the heating coils or the still surface (especially when direct heated) producing burnt flavours. Low flocculators often provide better attenuation (sugar utilization) and therefore higher alcohol yields. Filtering the wash before the distillation could be an option when using medium-high flocculators, but it is not apparently used in Scotland. The "on the lees" (ie wash containing the yeast cells) distillation is considered to enhance spirit flavour in both grain and wine spirits, most likely by increased fatty acid ester and methylketone concentrations producing oily, rancio and fruity aromas



Wort contains various sugars, mostly maltose and its oligosaccharides (maltotriose, maltotetraose, maltopentaose etc), but also glucose, fructose and sucrose. The oligo- and disaccharides (glucose, fructose, sucrose, maltose) are preferred by the yeast (figure 1) and transported inside the cell by diffusion, but maltotriose utilization depends on the yeast's ability to transport maltotriose into the cell by a spesific enzyme. Effective maltotriose uptake of a whisky yeast is important for optimal alcohol yield. Apparently most whisky yeasts (and brewer's yeasts) used contain several genes for maltotriose tranport enzymes, probably result from several hybridizations and chromosomal changes.


Figure 1. Sugar utilization in all-malt wort (IBD Blue book on yeast)

Alcohol tolerance of yeast depends on the strain and the species. Most domesticated or cultured beverage yeasts tolerate over 10% ABV ethanol concentrations as most non-saccharomyces wild yeasts stop working effectively in 1-5% ABV and die in about 10% ABV as some yeasts used for industrial fuel alcohol production can go up to 23% ABV. In whisky fermentations the factor limiting the final alcohol yield is usually the amount of sugars in the wort as whisky yeast attenuation is usually very good and the primary yeasts tolerate well the 5-8% ABV of a whisky fermentation.

The killer factors are toxins that yeasts produce against other yeast strains. Strains also develop tolerance for these toxins and there are many toxins in wild yeast fermentations, too. Brewer's and distiller's yeasts are usually quite tolerant to the most common killer factors and produce some killer factors themselves, depending on the strain. Anyway a wild yeast producing a killer toxin, which is not tolerated by the primary distiller's yeast used, might ruin the whole batch by producing a stuck fermentation or an inappropriate flavour profile.

Scotch malt whisky fermentations are not usually temperature controlled (apart from the starting temperature, which is adjusted to the ambient temperature), despite practically all lager brewers and most wine producers use temperature controlled fermetors. Yeast metabolism produces lots of heat, especially when anaerobically producing alcohol. Therefore whisky yeast must tolerate different temperatures, usually from 18-20C to over 33C. Typical whisky distillery yeasts tolerate about 32-34C depending on the ethanol concentration and although some other distilling strains can cope with up to 46C (a Finnish vodka strain), most distillers yeasts produce the best alcohol yield at 20-30C. Flavour compound formation is affected quite heavily by the fermentation temperatures; higher temperature fermentations produce less esters and more higher alcohols.

The most used whisky distiller's yeast in the latter part of the 20th century was a S.cerevisiae strain called DCL M, M-strain, Quest M, Rasse M, M-1, D1 or WH301 manufactured formerly by DCL Yeast ltd and now mostly by Kerry Biosciences (Kerry Group bought Quest Ingredients in 1998). The M-strain was introduced to Scotch whisky distilleries by DCL in 1952, but a similar Rasse M was used widely in German distilleries at least from the 1930s. The name has remained the same although the properties of the strain have changed considerably from the 1930s and there most likely is some variation between different yeast manufactures despite the same name. The M-strain is a intraspecies hybrid of S.cerevisiae (as S.cerevisiae covers the former S.diastaticus species). The first Scottish pure strain whisky yeast was developed in the mid-1920s and before the WW II DCL had pure cultures of "standard" DCL-whisky yeast, DCL S.C. (probably for sugar cane fermentations) and DCL L-3 (probably a variety of the standard DCL). Whether they were used widely in distilleries is not documented, but probably they were used in DCL grain distilleries and in some malt distilleries within a reliable transport route in adjunction with a local brewer's or baker's yeast. There is some evidence that the first pure-culture distilling yeasts were being tried in Keith already in the 1870s, but apparently they were never used in larger scale.

In continental Europe pure yeast cultures were more widely used and there were spesific strains for grain/malt worts (Rasse M, Rasse XII) and rye wort (R-strain) and even a raspberry-flavour producing strain "A". Also Fleischmann and Brown-Forman in the US had developed their own distiller's strains by the 1940s. The yeast strains of European, Asian and American distillers seem to be quite different at least by their genetics (see pic below), but there is no scientific data available for differences in spirit quality or flavour. The most similar beer yeasts compared to current Scottish whisky yeasts are probably some Belgian trappist and German hefeweisen yeasts, which are low flocculators, high attenuators, very alcohol tolerant and often produce smoky-spicy aromas associated with 4-vinyl-guaiacol production typical for S.cerevisiae var diastaticus, which is considered to have contributed strongly to the development of the M-strain from the ale-type S.cerevisiae.

Neighbour-joining tree of 63
S. cerevisiae strains (Schacherer 2009)

The M-strain ruled the Scottish whisky industry from 1960s to 1980s, although many distilleries used ale brewer's and/or baker's yeasts in adjunction with it. Before WW II most distilleries propagated their yeast on site, but during 1950s the production was largely outsourced to yeast factories and breweries. The availability of cheap (used/surplus) ale yeast diminished as lager became more popular in UK and as there were claims that using brewer's yeast dimished the alcohol yield, many distilleries started using pure cultures in the 1980s. As said before, the properties of the M-strain probably changed considerably during the latter part of 20th century, primary goals being higher alcohol yields and the preservation of traditional (or neutral) flavour profile.

Cream, compressed and dried yeast

Another significant development was the development of active dry yeast (ADY or instant dry yeast IDY) during the WW II to provide longer shelf life by basically drying the yeast into small pellets rather than just a big clump. This enabled the transportation of yeast into remote locations of Scotland, too. Some Scottish malt distilleries still use dried (95% solids) or more often compressed (25-28%) bag yeast. Cream yeast (17-23% solids) was introduced in 1983 to provide easy delivery by tank trucks and automated pitching, which was important and practical for bigger plants.

The MX-strain developed in the 1990s is a bit faster fermenter and produces a very similar flavour profile compared to the M, according to the manufacturer Kerry Group. The MX is faster and more efficient especially in high gravity worts which are preferred because of the savings in heating and water costs. Another common malt whisky yeast is Pinnacle by Mauri, which is an ethanol tolerant baker's yeast (S.cerevisiae) and actually slightly faster than MX, reaching peak fermentation speed about 1 hour earlier (at 15hours of fermentation) than MX. The grain distilleries use mostly cream yeast of undisclosed strain, produced by British Fermentation Products (BFP) or Anchor Yeast. In the table below you can find information about the yeast strain used by some Scottish distillers.

M	MX	MAURI	BREWER'S + DISTILLER'S	ANCHOR/BFP
Aultmore	Bowmore 25% (+Mauri)	Aberlour	Ben Nevis (50/50)	Auchentoshan (+Mauri)
Blair Athol	Bruichladdich	Ardbeg	Balblair	Daftmill
Bruichladdich (+Mauri)	Bunnahabhain	Auchentoshan (+Anchor)	Benromach	Grain distilleries
Bunnahabhain	Craigellachie (+Mauri)	Benrinnes	Cardhu
Glengoyne (+MX)	Glengoyne(+M)	Bowmore 75% (+MX)	Glenburgie
Glen Scotia	Lagavulin (+Mauri)	Bruichladdich (+M)	Glenmorangie (5dist, 2brew)
Highland Park	Speyside (+M)	Caol Ila	Imperial
Lagavulin (+Mauri)		Craigellachie (+MX)	Jura
Macallan (+Mauri+brewers)		Dalwhinnie	Longmorn
Speyside (+MX)		Glenfiddich	Macallan (+M+Mauri)
		Lagavulin (+M)	Miltonduff
		Laphroaig	Oban
		Macallan (+M+brewers)	Speyburn
		Strathmill (+brewers)	Strathmill (+Mauri)

Yeasts used by some Scottish whisky distilleries (Udo 2006)

The use of brewer's yeast as a secondary yeast strain produces more sulphury compounds into the wash and less fatty acid esters, especially when using dry ale yeasts. As brewer's yeast attenuates or even dies earlier than distiller's strain, the use of secondary strain increases the growth of lactic acid bacteria (LAB) towards the end of fermentation, which in turn lowers the pH of the wash altering the distillation process and produces specific flavours depending on the bacteria strain. One LAB strain might produce for example vinyl-guaiacol (smoky-spicy), as another produces damascenone (floral). Practically all the LAB growth results in more esters into the new-make, especially hexanoate and octanoate and decreased ethanol yield.

Because Scottish distillers at the present time use very similar primary yeasts, the selection of the strain of distiller's yeast is a minor factor in terms of flavour profile, at least when compared with other aspects of fermentation, such as original wort gravity, fermentation time and temperature and the material and microflora of washbacks.

In the future the whisky industry is looking to develop yeast strains suitable for higher gravity worts, shorter fermentation times and better utilization of maltotetraoses and -pentoses. Hopefully the flavour issues are also considered in the process and different strains are studied for improved flavour profiles.

REFERENCES AND FURTHER READING:

Bryce JH et al (ed). Distilled spirits: Production, technology and innovation. Nottingham Univ Press 2008
Dunn B, Sherlock G. Reconstruction of the genome origins and evolution of the hybrid lager yeast S.pastorianus. Genome Res 2008;18;1610-1623

Gray WD. Studies on the alcohol tolerance of yeasts. J Bacteriol 1941;42(5);561-574

Hansen R et al. Proteomic analysis of a distilling strain of Saccharomyces cerevisiae during industrial grain fermentation. Appl Microbiol Biotech 2006;72;116-125
Landry CR et al. Ecological and evolutionary genomics of S.cerevisiae. Molec Ecol 2006;15;575-591

Libkind D et al. Microbe domestication and the identification of the wild genetic stock of lager-brewing yeast. PNAS 2011;108;35;14539-14544
Piggott JR et al (ed). The science and technology of whiskies. Longman 1989

Pretorius IS et al. Designer Yeasts for the Fermentation Industry, Food Tech Biotech 2003;41(1);3–10

Querol A, Fleet GH (ed). The Yeast Handbook. Springer-Verlag Berlin 2006

Russell I (ed). Whisky, technology, production and marketing. Academic Press 2003
Udo M. The Scottish Whisky Distilleries. Black & White 2006

Saerens SMG et al. Genetic improvement of brewer’s yeast: current state, perspectives and limits. Appl Microbiol Biotech 2010;86;1195-1212
Schacherer J et al. Comprehensive polymorphism survey elucidates population structure of Saccharomyces cerevisiae. Nature 2009;458;342-346
Sipiczki M. Interspecies hybridization and recombination in Saccharomyces wine yeasts. FEMS Yeast 2008;8;996-1007
Suomalainen, H & Lehtonen, P. The production of aroma compounds by yeast. J Inst Brew 1978;85;149-156

Walker GM, Hughes PS (ed). Distilled spirits, new horizons: energy, environment and enlightenment. Nottingham Univ Press, 2010
White C, Zainasheff J. Yeast. Brewers Association 2010

Analysis of Michael Jackson's tasting notes

Michael Jackson

Michael Jackson (27.3.1942-30.8.2007) was the most influential beer and whisky writer of his time. He pioneered the writing of whisky tasting notes and also wrote many ground-breaking books on whisky manufacture and drinking culture. In the first edition of his most famous book, The Malt Whisky Companion (1989), he assessed 250 whiskies from 120 distilleries, a huge effort at the time. Based on his work Lapointe and Legendre (1994) studied the similarity of different whiskies. A total of 68 descriptors used five or more times in the book for describing basic malt whiskies aged circa 10 years were included in a matrix analysis to produce the dendrogram below to examine the similarities of different distilleries. Colour, nose, body, palate and finish descriptors were included. Some of the connections are quite expected, but for an average Scotch enthusiasist some are at the first glance somewhat compelling. That is probably because the descriptors are not scaled in any way and therefore the smoky notes in for example Aberfeldy and Glenugie are statistically just as strong as the smoky notes in Laphroaig. Also the amount of colouring, the cask-types and the maturation time of whiskies compared vary considerably. Anyway, despite these shortcomings, there is a highly significant correlation between the tasting notes and the geographic locations of the distilleries, especially in the 12 subgroups named from A to L. IMHO the dendrogram works pretty well in terms of grouping different styles of Scotch whiskies as well and at least is an eye-opener for some unpredicted similarities.

Lapointe 1994

The most common descriptors for each group are listed in the table below:

	color	nose	body	palate	finish
A	full gold	fruity, salty	medium	oily, salty, sherry	dry
B	amber	sweet, sherry	medium, smooth	dry, sweet	long
C	pale gold	sweet, salty	medium to full, oily	sweet, spicy	big, long, spicy
D	pale gold	fruity, grassy	oily	sweet, fruity	sweet, quick
E	pale wyne, gold	fruity, peaty	light	sweet, spicy	fruity
F	gold	aromatic	medium, smooth, light	sweet	sweet
G	gold, full gold	grassy	smooth, light	grassy	dry
H	white wyne, pale	sweet	smooth, light	sweet, dry, fruity, smoky	dry, light
I	gold, full gold	dry, peaty	medium, light, firm	dry, smoky, sweet	salty
J	full gold	dry, peaty, sherry	light to medium, round	sweet	dry
K	gold, full gold	sweet, dry, peaty	medium to full	sweet, dry	dry, long
L	full gold	aromatic, peaty	medium	sweet, smoky	smoky

...and the best whiskies of each subgroup are listed here:

	average	best in basic malts	pts	best in book (1st ed)	pts
A	75,3	Laphroaig 10	86	Laphroaig 15	89
B	80,0	Highland Park 12	90	Macallan 25	95
C	78,5	Talisker 10	90	Talisker 10	90
D	69,5	Auchentoshan 10	85	Auchentoshan 18	86
E	74,8	Bladnoch 8	85	Bladnoch GM1975	86
F	76,5	Springbank Cad15	88	Springbank Cad21	92
G	79,1	Cragganmore 12	90	Cragganmore 12	90
H	69,2	Bruichladdich 10	76	Glenfiddich 30	86
I	79,9	Longrow 14	90	Lagavulin 16	95
J	72,8	Linkwood 12	83	Linkwood GM25	87
K	74,0	Dallas Dhu GM1971	85	Dallas Dhu GM1971	85
L	73,3	Lochnagar 12	80	Lochnagar NAS	83

An interesting fact in MJ's tasting notes is that there is a significant correlation between colour, body, palate and nose, but the finish notes do not correlate with the classification derived from the other descriptions. As expected the correlation between the nose and the palate is extremely strong, but there is also a very strong correlation between the colour and the body (texture) of whisky, which might support the hypothesis that added caramel colouring affects the body (or mouthfeel) of whiskies.

Legendre 2004

REFERENCES AND FURTHER READING:

Jackson M: The whole bibliography.

Lapointe FJ, Legendre P. A classification of pure malt Scotch whiskies. Appl Statist 1994;43;1;237-257

Legendre P, Lapointe FJ. Assessing congruence among distance matrices: single-malt Scotch whiskies revisited. Aust N Z J Stat 2004;46;615-629

Mantel N. The detection of disease clustering and a generalized regression approach. Cancer Res 1967;27;209-220

Sokal RR, Rohlf FJ. The comparison of dendrograms by objective methods. Taxon, 1962;11;33-40

Ward JH. Hierarchical grouping to optimize an objective function. J Am Statist Ass 1963;58;236-244

Yeast in the 1800s

Pic from sandcreekbrewing.com

Yeast is a crucial element in all alcohol production. It converts sugars to alcohol and CO2 and its metabolism also produces a variety of flavour compounds. Yeast has been used in distilling probably from the beginning, although its importance was not fully appreciated until the late 19th century. Early distillers used beer yeast, wine lees and sometimes fruits or juices to improve fermentation and at least some re-use of distilling yeast has been done in the 1700s. In the process more alcohol tolerant and temperature resistant yest strains have been evolved and/or selected. Some distillers (and some wine makers) in the continental Europe used fermentation sticks, for example branches of hazel, which were used to stir the wort. In the process the stick was covered with yeast and acted as an inoculator for the next batch. During the 1700s the Scottish distillers sold considerable amounts of excess yeast from the fermentations to bakers, but also bought ale yeast from breweries.

Bass brewery fermentations, late 19th century

In the 1823 Excise Act the distillers were given substantial reductions on taxes to persuade them to apply for a legal licence. At the same time the yeast trade was handed over to brewers as the law was (at least interpreted) to prohibit the distillers to remove any excess yeast during fermentation. As the wort destined for distilling was not traditionally boiled, its contamination with bacteriae and wild yeasts was inevitable and therefore the yeast slurry at the end of the fermentation was not very healthy or pure and  the re-use of distilling yeast was not popular. Porter yeast was preferred by many distillers, because it tolerated high gravity worts and temperature fluctuations and was believed to produce heavier style of spirit and better alcohol yields. Propagating yeast for several batches from starters acquired from the breweries was probably the method of choice for many distillers and the starter was replaced with fresh brewers' yeast as it contaminated or lost viability.

In the continental Europe distillers collected their excess yeast in the process and in 1847 the Vienna Process (or Mautner process) was invented to produce great amounts of yeast from corn based fermentations. Basically this was done with acidic, high gravity-high temperature brewing and top-cropping the excess yeast with nets. The yeast was further processed by partial drying with nets and starch, which improved the stability and eased the transportation.

As the yeast production of UK brewers was not sufficient for the increased bakery industry and the distillers were not allowed to sell their yeast, the British yeast industry became controlled by the Germans, French, Dutch and Belgians. Brewers' yeast produced bitter bread, because of hops, contaminant bacteriae and the properties of the yeast strains used,  and therefore imported yeast was preferred in bakeries. There were various methods to remove the bitterness from the ale yeast, but they increased the cost of manufacturing, which was already much more than in the big grain distilleries. The UK Distillers used mostly domestic porter or ale yeast, although some bakers' yeast and imported yeast was also used, especially during the summer breaks of the breweries. In 1860 distillers were allowed to collect yeast of a total amount of 2,5% of the volume of wash and in 1880 this was increased to 10%, probably to diminish the role of "German yeast monopoly". Dr William S. Squire patented his efficient yeast manufacturing process in the UK and offered rights to the Distillers Company Limited (DCL) in 1881. Experimental yeast manufacturing started first in Cameron Bridge and Kirkliston grain distilleries during 1882 and in 1885 a larger scale industrial production was started in Cameron Bridge. Alfred Barnard described The Cameron Bridge Yeast House in 1887: 

"Near the works, and standing in a small park, is a handsome building which we at first took for a church, but on enquiry we learned that it was the Yeast House, erected by the Company for the manufacture of French yeast, a large quantity of which finds its way to Glasgow and London, where its fine quality is much appreciated, and yields a large revenue."

The grain distillery Glenochil (DCL) did also produce yeast at the time of Barnard's visit (although probably not yet by the Squire's method): "The Company manufacture an enormous quantity of what is called German Yeast, considered superior to that manufactured on the Continent, and which commands a good price in the market." 

In the Cambus distillery (DCL) there were plans to start yeast production: "Alongside the Water-wheel House entrance, across the lade, is a large building fitted up with machinery for making German Yeast, where about two tons can be produced weekly, but at that time of our visit this department was silent." 

Bo'ness in Linlithgow owned by J.Calder & Co.  operated according to their own methods imported from Germany and were more open about their process than the DCL: "Under the principal Tun Room is the patent Yeast House, where a large an remunerative business is carried on. Here the yeast from the fermenting backs is collected into three tanks. Afterwards these yeast skimmings are pumped into accordion shaped iron press- a German patent- containing twelve leaves or intersections, which are covered inside with linen cloth of various textures, forming separate divisions, through which the yeast is driven y great pressure. The dough-like material, which exudes from the last intersection, is then collected and passed through a fine sieve, whilst the liquid expressed or squeezed therefrom runs into tank. The yeast material left in the sieve, which looks like flour cakes, is afterwards weighed out in 7, 14, and 28 lbs, and pressed into conical bags and shipped off to England and Germany."

The  DCL yeast business was not fully engaged or even appreciated in 1887, producing just over 5% of the total profits of DCL, but with its wide distiribution network the DCL gained practically a domestic monopoly over the yeast in the 1890s and the foreign imports declined from 14,2 tons to 6,5 tons in 1887-1901 and stopped completely before the WW I. In 1894 production was started in Carsebridge and Glenochil. DCL made good profits in the yeast trade (up to 35% of total profits in 1894-1895) and the trade partly helped it through the Pattison crisis at  the turn of the century. In 1922 DCL had acquired all the yeast producing grain distilleries and controlled the yeast industry as German imports were down after the war.

The role of yeast in fermentation was surprisingly poorly understood until the late 1800s. Fermentation was believed to occur chemically, in another words sugars and water would turn into alcohol and CO2 in the presence of sufficient heat and air; yeast was considered as a byproduct. The Theory and Practice of Brewing by Michael Comburne (1762) describes fermentation as follows:

"The sensible internal motion of the particles of a mixture, by the continuance of this motion particles are gradually removed from their former situation, and after some visible separation, joined together in a different order and arrangement so as to constitute a newcompound...vegetable fermentation is the act of which oils and earth,naturally tenacious, by the interposition of salts and heat, are so much attenuated and divided, as to be made invisible with, and to be suspended in, an homogeneous pellucid fluid...the acid particles of the air, which insinuate temselves into the wort, act on the oils, and excite a motion and effervescence, which is the cause of the heat. As the internal motion goes on, the particles of the wort become more pungent and spiritous, become more fine and active: some of the more volatile ones fly off, hence the dangerous vapour called gas. The pressure of external air, from the very first of its fermenting, not only occasions the particles of wort to arrange themselves in their due order, but also by the weight and action of that element, grinds and reduces them into smaller parts. That this operation persists even after the liquor becomes fine is evident, for every fretting is a continuance of fermentation. It would seem that the more minutely the parts are reduced, the more pungency will appear, and the easier their passage be in the human frame. Lastly, in the final state of all, the active particles being entirely evaporated, a pellicle forms on the surface, seeds deposit from the air, and a moss grows." "Yeast is needed to excite the separation and new arrangement on which the perfection of the products depends, and prevent the accidents to be apprehended from worts' disposition to ferment spontaneously through slow absorbtion of air from the atmosphere." "Yeast provides bladders of the coarser oils of wort, filled with air and ready to start the motion."

A French scientist Antoine Lavoisier described the fermentation process quite accurately in 1789 as "grape must=>carbonic acid+alcohol" and in 1815 the yield of alcohol from sugar was estimated almost precisely by Joseph Gay-Lussac. Many scientists (Christian Erxleben 1815 was probably the first) of the early 19th century proposed that yeast was a living organism and that fermentation was "of some vegetal or animal origin" and as the microscopes improved, three scientists described yeast cells almost simultaneously but independently (Cagniard-Latour, Friedrich Kützing and Theodor Schwann, 1837). Schwann wrote that


"wine fermentation must be a decomposition that occurs when sugar-fungus uses sugar and nitrogenous substances for growth, during which, those elements not so used are preferentially converted to alcohol".

Saccharomyces cerevisiae

This "vitalist" theory of fermentation was strongly opposed by chemists and it was until 1879 when Louis Pasteur confirmed and described the fermentation process by yeasts. Shortly after that in 1883 the first pure yeast culture (a lager yeast Saccharomyces carlsbergesis, later S.uvarum, S.cerevisiae and S.pastorianus) was isolated in the Carlsberg brewery by Emil Christian Hansen. At about the same time truly sterile laboratories and agar plates were introduced which made possible to isolate and transport pure yeast strains. 

After these findings, the the era of biotechnology really started and in the 1900s more efficient and pure yeast strains were developed. In the UK the yeast biotechnology was slower to start as breweries were conservative about pure strains and lager brewing. The DCL started to actively to develop a pure yeast strain for (grain) whisky distilling and yeast production in 1911, as they learned that The Berlin Distillers' Association had already developed a successful strain, which they used in all their distilleries. Several cultures were grown and considered, but the first suitable strain was developed not until the mid 1920s. As the whisky industry was declining and the trade of industrial alcohol increased the emphasis was heavily on alcohol yield. More about yeast strains and their influence on brewing and flavours in the following posts...

REFERENCES AND FURTHER READING: 
Barnett JA. Beginnings of microbiology and biochemistry. Microbiology 2003;149;557-567
Comburne, M. The theory and practice of brewing. Haberkorn 1762

Fitzgerald M. Industrial combination in England. Ayer publishing 1927.
Udo M. The Scottish whisky distilleries. Black&White Publishing 2006.
Weir R. The history of the Distillers Company 1877-1939. Clarendon Press 1995.
Weir R. Science marketing and foreign competition in the yeast trade 1860-1918. Business History 1991;33;4;43-67
White C. Yeast, the practical guide to beer fermentation. Brewers Association 2010.

Flavour wheels

Classification of odors is a hard task. There are no generally accepted descriptors for odors and there are no measurable and defined primary odors. Cultural differences may be enormous because the smells can be perceived, learned and memorized as objects resembling something, often an another sensation by for example sight or sound or even as feelings or memories. The olfactory sensation is processed quite roughly in the subconscious brain and therefore it is harder to concentrate on details, unlike for example sight or hearing.

Various attempts have been made to classify odors. The western method has mostly tried to describe odors by naming them after familiar objects or groups of objects (lemon, fruity, flowery, spicy etc.). The Asian cultures seem to perceive and classify smells often more aestetically or subjectively (assessed by man or god). In Indian hindu and buddhist traditions the classifications of odors were simply good/bad and even/uneven (although this might also be translated faint/strong). A hindu might further divide odors into more descriptive sweet, pungent, diffusive, compact, smooth, rough and pure wehreas a buddhist might separate root-, stalk-, branch-, leaf-, flower- and fruit-odors. Most meats are often described as bad odourants in India, especially when raw, this is probably due to the strong vegetarian culture present in India.

One of the early written western classifications was made by the Swedish botanist Carl von Linne. His odores medicamentorum (1752) lists seven primary odors: Aromaticos (aromatic), fragrantes (fragrant), ambrocacos (ambrosial, musky), alliaceos (onion, garlic), hircinos (hircine, goaty), tetros (repulsive), naufeofos (nauseous). Zweibakker (1895) added another two odors: ethereal (fruity) and empyrheumatic (burnt). Henning (1915) contructed this into a prism, representing the links between different groups. For examples of cultural variation see the odor classifications of Serer Ndut tribe from Senegal and Sua Indians of Brazil in the tables below. 

Odor	Example
Urinous	Europeans,horses,dogs,cats,plants used as diuretics,squash leaves
Rotten	cadavers, pigs, ducks, camels, creeping plants
Milky/Fishy	nursing women,neighbourhood tribes,goats,cows,antelopes,jackals,fish,frogs
Acidic	spiritual beings, donkeys, tomatoes, trees, roots
Fragrant	Seret Ndut, Bambara (friendly tribe), flowers, limes, peanuts, onions

Table1. The odor classification of Serer Ndut in Senegal.

Odor	Example
Bland	adult men,small mammals,small birds,fish,innocuous plants
Pungent	old men,old women,large mammals,macaw,amphibians,medicinal plants
Strong	adult women,children,carnivorous mammals,birds,harmful plants

Table2. The odor classification of Sua Indians in Brazil.

Many odor classifications might seem quite strange for someone from a different culture (although it would be great to see some whisky tasting notes by a Serer Ndut). But as you learn that onion essence is a popular compound of perfume in Africa and consider that fish and milk probably turn sour and rancid in the heat practically instantly, maybe some logic starts to emerge. But the bottom line is that there are no really universal, constant and non-culture related descriptors or classifications for smells.

A common method of classification in the late 1900s was a wheel, basically developed from the Linné-system by adding classes and simplificated from the 3D-model of Henning to one (simple circle) or two dimensional (circle with tiers). The flavour wheels have a lot in common as they are descriptive systems constructed by people from similar cultural background (educated Europeans / Americans) and probably because many have most likely been developed from the succesful wine wheel by Ann C. Noble (1990). The wheels detailed according to their use, but basic principle is often quite similar. Most wheels concentrate on the smell, but many have at least some basic taste descriptors included although none seems to list umami; for example an Asian whisky wheel would probably be quite different providing perhaps umami, soy and more than one subcategory of spices. Trigeminal activity (camphor, burning sensation) is quite usually covered in the wheels, but mouthfeel, viscosity and texture are noted surprisingly seldom. Some wheels have apparently been made from the production point of view, such as the Dewar whisky wheel and to some extent the early version of Scotch Whisky Research Institute wheel. Probably the most detailed whisky flavour wheels used are the Revised Scotch Whisky Flavour Wheel for Industrial Purposes and the Whiskymag wheel. Below you'll find some other wheels for beer, chocolate, tequila, olive oil, cigars, cheese, bodyodor and off-odors.

Wine wheel (Ann C Noble)

The Dewar whisky wheel

SWRI wheel

SWRI revised wheel

Whiskymag wheel

Macallan wheel

Coffee wheel

Fragrance wheel by Michael Edwards

Chocolate wheel

Olive oil wheel

Cigar wheel

Comté cheese wheel

REFERENCES AND FURTHER READING:

Classen C et al. Aroma: The cultural history of smell. Routledge, 1994
Lawless HT. Exploration of fragrance categories and ambiguous odors
using multidimensional scaling and cluster analysis. Chem Senses
1989;14:349– 60
von Linné C. Dissertatio medica odores medicamentorum exhibens. 1752
McHugh J. The classification of smells and the order of senses in Indian religious traditions. Numen 2007;54;374-419