My old pal in Ol' Blighty, Susan Jordan, posted this on FB today:
The science and art of whisky making
Andy Connelly describes how base beer is transformed into golden whisky – the drink of angels and hairy Scotsmen
"... drinking whisky is never about just drinking whisky; we're social creatures and we tend to drink in a social context... Even if we resort to drinking alone, we drink with memories and ghosts."~~ Iain Banks
If you are lucky enough to be reading this with a glass of whisky in your hand then take a second to regard the contents of your glass. Is it a pale golden or dark ruby colour? Does it greet your nose with memories of heather moorland or salty coastlines? Is your mouth filled with a honey sweetness or a dark acrid smokiness? All of these and many more are possible from the most multifaceted of spirits known variously as whisk(e)y, liquid sunshine, and the water of life.
Whisky is the liquid gold that emerges from the distillation of base beer. It is "the separation of the gross from the subtle and the subtle from the gross ... to make the spiritual lighter by its subtlety" (Hieronymus Brunschwig, 15th century doctor and distiller). Almost all spirits are produced by distillation: a liquid with a low alcohol content such as wine or beer can be taken and from it a spirit produced. Alchemists believed that through repeated distillation they could extract the essence or spirit of a material and that from wine they could extract the aqua vītae or water of life. The word itself, whisky, is an Anglicised version of the Gaelic for water of life: uisge beatha or usquebaugh is what Irish and Scots monks called their distilled barley beer.
Scotland's mild, maritime climates, with long hours of daylight in summer, was ideal for growing barley for making beer. Thus, the Scots distilled beer not wine, and so made whisky not brandy. The first evidence of whisky production in Scotland comes from an entry in the Exchequer Rolls for 1494: malt is sent " ... to Friar John Cor, by order of the King, wherewith to make aqua vitae". Since then whisky has been as intimately associated with Scotland as the kilt and Tunnock's caramel. However, it is not thought to be a Scottish invention. Whisky making is most likely to have developed in Ireland and have been carried across to Scotland by monks some time between 1100 and 1300.
The processes that go into making whisky appear simple but they can produce an infinitely complex and subtle drink. Whisky can be made from many different grains but a Scottish single malt can only be made from malted barley. Scottish single malt is what we will concentrate on here as there are many more whisky distilleries in Scotland than anywhere else in the world.
Step 1: Make a simple beer
Like most processes based on fermentation, beer making is the conversion of sugars into alcohol, using yeast. In wine making these sugars come from grapes, in beer making they come (in the majority) from malted barley.
Malting, carried out by maltsters, is the process of extracting the sugars from barley. It begins by soaking the barley in water to allow the barley seeds to germinate. During germination enzymes turn the starch within the barley into soluble sugars. After two or three days the germination is stopped by drying. This drying process is critical to the taste of the beer, and so the whisky. In many parts of Scotland, especially on the Scottish islands, drying was traditionally done using the local fuel peat to fire the kilns. Phenolic compounds transferred from the peat giving the malt, and so the whisky, its signature smoky peaty flavour. The greater the amount of peat used, the more peaty and smoky the whisky.
The malt is then ground and hot water is added to extract more fermentable sugars. The liquid that is drained off after this process is called the wort. Yeast is added to the wort which is allowed to ferment giving a rough beer called wash (7-10% alcohol).
Just as different grape varieties are used in wine production, there are a number of different barley varieties that can be used for the distillation of Scottish single malt whisky. If any other type of grain is used (such as maize, buckwheat, rye, corn, etc.) the result cannot be called single malt whisky.
Step 2: Distillation of the beer
Distillation works because different liquids boil (evaporate) at different temperatures. The boiling point of alcohol is 65-80 °C, depending on the type of alcohol, substantially below water's 100 °C. This means that as a mixture of water and alcohol is heated, more of the alcohol than the water will be released as vapour. These vapours are collected or condensed on a cold surface, similar to the water droplets on a pan lid when you boil water. In fact, the word distil comes from the Latin destillare, "to drip".
Scottish whisky is generally distilled twice. The first still is called the "wash still", and is used to separate alcohol from the wash. The wash still produces a spirit called low wines (21-28% alcohol). These low wines are then transferred to the "spirit still", which separates out the drinkable alcohol.
During heating, the condensed vapour is separated into three parts or cuts. The first cut is called the heads or foreshots and contains a high proportion of toxic methanol and acetone and other low boiling point liquids. As the temperature increases, the next cut is called the 'heart of the run': this is the spirit that will evolve into whisky. With more time and temperature the vapour decreases in alcohol and increases in water content. This third cut is called the tails or feints, and includes a host of aromatic compounds that give desirable flavours. However, some are only in small quantities, such as fusel oil.
Fusel oils are longer chain (higher) alcohols than ethanol. They are mildly toxic and in high concentrations have a strong disagreeable smell and taste (fusel being German for "bad liquor"). In small concentrations, however, they give the whisky flavour and body.
The craft of the stillman is to know at what point to draw the boundaries between these cuts; each distillery will take a slightly different fraction so each spirit is chemically different before it even gets into the cask to mature.
The "new make spirit" produced at this point is about 70% alcohol. It is what would have been drunk in the early days of whisky, straight from the still, like vodka. It was only discovered in the 16th century that over time whisky kept in oak casks would evolve and mellow becoming something greater and more complex. But what is this evolution and why does it happen?
Step 3: Storage and maturation in oak casks
When alcoholic liquids are stored in new oak casks several things occur. First, the liquid extracts soluble materials from the wood that contribute colour and flavour, including tannins, oak lactones (a coconut flavour), clove and vanilla aromas. These flavours, particularly vanilla (vanillin in oak, the same compound found in vanilla pods), can be very strong in new barrels, hence second hand casks are desirable for Scottish whisky as they give milder flavours.
The inner surface of the casks is generally carbonised by burning. This acts like an activated charcoal absorbent, removing some materials from the whisky and accelerating chemical interactions between wood and whisky. The browning-reaction products of burning and smoky volatiles formed are also extracted by the whisky, giving flavour and colour.
Every cask "breathes" while it matures. Gaps and pores in the wood allow the liquid to absorb limited amounts of oxygen which leads to oxidation of alcohols and aldehydes. Acids also react with ethanol to form esters, some of the most aromatic and often fruity of whisky's flavour compounds.
The wood of the casks expands during the heat of summer and contracts during the cold of winter. As a result of evaporation the whisky will annually lose up to 2.5% alcohol while it matures. The part of the maturing whisky that vanishes between casking and bottling is called the angels' share.
The first whisky casks would have been old oak sherry casks from Spain which arrived in the British Isles for bottling. Sherry was very popular in the 16th century and so the casks could be bought relatively cheaply. Now ex-American bourbon casks are generally used as they are cheaper than old sherry or wine casks, although some whiskies are still matured or "finished" in sherry or wine casks.
The size of the cask, the position in the warehouse, the type and previous life of the oak, the temperature and humidity, and many other difficult-to-define variables contribute to the final whisky flavour. This multitude of variables means the age for optimum flavour development changes drastically from distillery to distillery, or even from cask to cask. Some whiskies are best after eight years while others are best after 16; there are no rules, just tasting. This is why the process of "blending" is so important, even in single malt whiskies.
Step 4: Blending and bottling
A single malt whisky is a 100% malted barley whisky from one distillery, blended or mixed from many casks to give the desired colour and flavour; the age on the bottle indicates the youngest whisky in that blend. The process of blending a single malt is complex and highly skilled; if distilling is a science then blending is definitely an art.
Once the whisky is blended it is usually diluted to the final bottle concentration. The source of the water used at this point is considered of great importance and whisky distilleries will guard their water source carefully. Caramel is sometimes added at this point to adjust the colour of the whisky.
The whisky is generally diluted to a bottling strength of between 40% and 46%. Occasionally distillers will release a "cask strength" edition, which is either undiluted or diluted only a little and will usually have an alcohol content of around 60%.
The dilution of whisky is more complex than just the addition of water. Some chemicals within whisky (particularly fusel oils and fatty acids) have limited solubility in water. When whisky is diluted with water to 40% alcohol these oils can give the whisky a cloudy appearance, and so for improved shelf appearance they are generally removed by cold filtering.
Step 5: Drinking and appreciation
No matter how many years a whisky has been maturing, whatever the idyllic Scottish island from which it came, and whatever the long history, whisky is there to be drunk. Hopefully drunk as a pleasurable experience, savoured and appreciated. So if you have the chance, spend some time with your glass of whisky as you might with a good wine. Try using a wine or a brandy style glass instead of a tumbler for an enhanced experience.
The colour of the whisky is the first thing you see in your glass. The colour can give a clue to the type of cask used. Single malts that were matured in bourbon casks, for example, are usually a golden-yellow/honey colour; whiskies finished in sherry casks are usually darker and more amber in colour.
The next sensory experience is the smell. Put your nose to the glass and take a gentle sniff. What do you find? Is there a hint of that peated malt? Or a little of that vanilla from the oak cask?
The chemicals that are reaching your nose are a complex mixture, the culmination of distillation and years maturation. But they are not a fixed set, you can still alter and change the bouquet that greets your nose and so the flavour of the whisky simply by adding water. Adding water to whisky changes the concentration of alcohol and so increases the volatility of alcohol-soluble hydrophobic or long-chain compounds such as the fruity esters, increasing the fruity aspects of the whisky's flavour.
In contrast, smoky phenolics and roasted nut and cereal-flavoured nitrogen-containing compounds are water-soluble, and the volatility of these is reduced with water addition and so the smoky aspect of the whisky's flavour is reduced. However, the addition of ice reduces the temperature of the whisky and hence reduces the volatility of all the compounds, leading to a reduced aroma and a diminished taste.
Good whisky needs time, both during maturation and in the glass. Sip the malt slowly. As you roll it around your tongue let the flavours take over your mouth and savour the warmth rolling down your throat. Hold up your whisky against the light, ponder the centuries of history, discovery and chemistry behind the golden liquid. Drink deep, drink to make your spirit lighter and remember that you drink where angels have been before you; angels and hairy Scotsmen.
Andy Connelly is a cookery writer and former researcher in glass science at the University of Sheffield. He is training to become a science teacher