First you need raw materials with a source of sugar as well as flavours (often referred to as congenors) to make spirits. If the raw materials are starch (and inulin) based e.g. wheat, barley, potatoes etc., these need to go through a conversion process (typically heat orientated) to create a sugary liquid that can be fermented.
Some distillers grow their own raw materials, e.g. various Cognac producers grow their own grapes (6 white grapes are permitted for use in Cognac, however, Ugni Blanc, called Trebbiano in Italy, is the key variety). Many buy in the raw materials, e.g. Scotch Whisky producers often buy their grain from a variety of countries. Either option, the quality of the raw materials distillers use plays an important role.
Yeast and sugar are both critical for fermentation and yeast is a scavenger whose favourite food is sugar. Yeast, its scientific name is saccharomyces cerevisiae, is a single-celled fungi. It’s not just used in the alcoholic fermentation process, it’s also used to leaven bread, responsible for the mould that ripens blue cheese and even the moulds that produce antibiotics for the pharmaceutical and veterinary industries.
Fermenting liquid where the yeast is consuming the sugar to convert it into alcohol, CO2, flavours and heat
In the alcoholic fermentation process, the yeast consumes the sugar for energy and growth, and produces not only alcohol but carbon dioxide, flavours (congenors) and heat. The higher the level of sugar in the raw materials, the more sugar the yeast can potentially convert into alcohol. This explains why alcohol levels in wine can be considerably higher where the grapes have been grown in hotter climates as they are riper with higher levels of sugar.
sugar + yeast = alcohol, CO2 , flavours & heat
Fermentation occurs naturally as yeast lives on the fruit, vegetables and so on. These are referred to as wild or ambient yeasts and can be used for alcoholic fermentation. Many wineries and distilleries opt for laboratory cultured yeasts as they provide greater consistency in the end products that can be helpful for brand style. Some use a combination of both types of yeast.
For alcohol liquids destined for distillation, these are often fermented to between 8-10% abv (alcohol by volume i.e. the alcoholic strength you see on spirit (and wine) labels).
The aim of distillation is to increase the alcohol level in the fermented liquid and to select and concentrate the flavours (congenors). This is done by putting the alcoholic fermented liquid, which contains a lot of water, into a still and applying a heat source.
As water boils at 100ºC and ethanol at the lower 78.3ºC, if the heat is applied carefully the first vapours that will rise are alcoholic ones. These vapours rise through the still and enter a connected condenser which has a cooling source (e.g. cold water filled pipes/jacket) converting the vapours back into liquid form. The new liquid has more ethanol than the original liquid. Think of boiling your kettle or cooking in the kitchen, the steam rises and hits the cool windows and then water runs down the window. Same principle
There are essentially 2 types of stills:
Pot stills are made of copper as this metal is easy to shape and a great conductor of heat. This is a batch process as the alcoholic liquid requires more than one distillation.
Pot stills are more labour and time intensive. These are ideal if the distiller wants to make flavoursome and lower alcohol spirits. Sometimes legislation stipulates their use e.g. Single Malt Scotch Whisky.
The 1st distillation, which can take a couple of hours to around 5 hours, separates the alcohol from some of the water and no cuts are made. The alcohol is typically between 25-30% abv at this point. The liquid is stored in stainless steels tanks until required.
The 2nd distillation concentrates the alcohol of the 1st distillation and the heads and tails from previous second distillations i.e. it’s a more complex liquid. The distiller can select or reject particular congenors and this time does makes cuts. The cuts relate to the heads (first off and very solventy i.e. paint like), the desired heart (next off and typically around 75% abv) and the tails (last off and when cheese and plastic aromas start to appear). For each cut selection, the distiller just re-directs the flow of the liquid. The earlier the cut point the lighter the style and the later a richer style.
Whilst designs do vary the same principle applies. This type of still was invented to enable continuous spirit production and reduce costs in terms of labour and time required.
Continuous stills are column shaped and unsurprisingly sometimes called Column Stills. They have a heat source, typically high-pressure steam pumped up from the bottom of the still, and perforated plates where multiple mini distillations take place. This happens as liquid forms on each plate, the vapours are forced through the liquid and the most volatile rise to the plate above whilst the least fall.
Using the viewing plates, the distiller can monitor and draw off the liquid at the desired abv. The higher up the still the liquid is drawn off, the heads, the higher its abv versus the lowest, the tails, the lower abv.
Continuous/Column stills are ideal for highly rectified spirit (HRS) production, e.g. vodka, as they can reach 96% abv if the still has enough plates.
All newly made spirit is dry and colourless off the still. Distillers, subject to legislation, can adjust the colour (typically using tasteless food grade caramel colouring albeit liqueurs have a vast colour range), flavour, sweetness (can help the balance and style, plus a legal requirement for liqueurs) and alcohol levels.
Unaged v Maturation
Spirits can be unaged or matured. Some newly made spirits are kept in inert stainless-steel vessels and remain colourless. If they are left for a period of several months, they can become smoother and more mouth filling but will still remain colourless.
Other spirits are matured in wood, typically oak, which softens the spirit. Maturation is an important source for colour and flavour. The impact of the wood on the spirit can depend on many things e.g. source of the wood (i.e. French and American oak have different flavour profiles); level of toasting when the barrel was constructed (i.e. by legislation USA Bourbon must be aged in brand new charred wood); size of the barrel (relates to liquid/wood ratio i.e. larger barrels have a lower impact versus smaller barrels a greater impact); length of time in the barrel; previous contents; whether the spirit has been transferred for finishing (i.e. some whisk(e)y is finished in another type of wood for example many Scotch Whiskies are matured in ex Bourbon casks before being moved into ex Sauternes/Port/Sherry etc. casks in the latter maturation stages to add additional complexity); and even warehouse temperatures (heat speeds up the maturation process and increases oak influence).
Blending is a common procedure as it helps with consistency, which is important for brand style/taste. Differences in spirits can be a result of the different woods used, ages of the spirits, distillation strengths or methods and also there can be variations, sometimes considerable, barrel to barrel.
Old spirits can lack balance and be pretty hard to enjoy and new spirits can lack any depth or complexity. Blending a bit of older spirit into younger ones can increase the balance and complexity neither had individually.
Blending is an art where the aim is to produce a spirit that is better than the individual spirits themselves
Spirits are diluted using demineralised/completely pure water to bring them down to bottle strength e.g. what you buy them at. The vast majority of spirits are around 40% abv. The legal minimum in the EU is 37.5% abv and USA 40% abv. The USA uses a proof system too which equates to 2 x the abv e.g. 40% abv would translate to 80% proof.