With St. Patrick’s Day on the horizon, we’ve got Irish whiskey on the mind, so we thought we’d take you through the hows and why of triple distillation. 

Irish whiskey doesn’t have any kind of monopoly on triple-distilling its whiskey, nor does the process define Irish whiskey. Auchentoshan, Rosebank, Hazelburn (from Springbank), and Woodford Reserve all use three stills to make whiskey and there’s often nothing stopping anyone else from doing it across the world. 

But it’s fair to say that the technique is associated with Ireland more than any other country. When Alfred Barnard visited while researching his 1887 classic The Whisky Distilleries of the United Kingdom, 20 of the 28 Irish distilleries he saw practised triple distillation. At giants like Bushmills, Tullamore D.E.W., and Midleton Distillery (home of Jameson, Redbreast, Powers, the Spot whiskeys, and more), the process is used today and is favoured among many of the new waves of producers. There are always exceptions, like Cooley or Waterford, who use double distillation. 

The origins during the 19th century seemingly point to a third distillation being an elegant solution to the inadequate spirit that unmalted grain and the large stills could produce. That’s not why it’s practised today though, so with St. Patrick’s Day on the horizon, we thought we’d do a little breakdown of the process of triple distillation: how it works and the way it affects the flavour of the whiskey. To do that, we first need to cover batch distillation.

The three stills at Midleton Distillery

The three stills at Midleton Distillery.

The basics of batch distillation

Whenever you distill whiskey in pot stills, you’re undergoing batch distillation. As the liquid runs through the stills, it’s being separated and concentrated in stages. Often, this is done twice, first in a wash still and then in a spirit still. Your wash (a fermented alcoholic liquid, akin to beer) is boiled in the wash still, the liquid forms a vapour, which through the wonders of physics contains more alcohol than the boiling liquid. 

The vapour will also hit the copper sides of the still, and more of the water in the vapour will condense and fall back into the liquid (known as reflux), increasing the separation of alcohol and water.  This effect is called rectification. This vapour is diverted away from the still, cooled down and collected. The distillate that comes off the wash still, which is now called low wines, is around 25% ABV. You then distill those in the spirit still (along with some leftovers from your previous distilling) concentrating the alcohol to around 70% ABV. This spirit is then collected and matured.  

During batch distillation, distillers can dictate the profile of the spirit they’re making with something called cuts. What they’re selecting is the kind of congeners (flavour compounds) they want in the distillate, these are present in the grain and also develop during fermentation, distillation and maturation. The more volatile congeners, like methanol and esters (fruity congeners), come off first. These are called are your foreshots or heads (they have lots of other names too!) and are cut where the distiller chooses. They then collect the ‘heart’, the main body of the distillate that is used for the final spirit, what remains is a solution with the majority of higher alcohols (fusel oils) and the least volatile congeners, the feints or tails (again lots of other names for this).

How much or little of each you want to remove depends on the final spirit you want to create. Unwanted congeners can be removed by increasing the amount of reflux in the still. A larger/taller still shape encourages more reflux, as does using an upward lyne arm, or boil balls. Sulphur compounds can be removed by using a special type of metal, which reacts with the sulphur. Any ideas? You guessed it, copper.

Triple distillation explained

Triple distillation: make sense?

The feints still

Or, you can add an intermediate still in between them, often called a ‘feints still’. In this process, the distillation starts in the wash still with the 8% ABV being fed in as usual. In triple distillation, this stage is all about extracting alcohol and flavours from the fermented wash to create a low wine around 22%-50% ABV, usually on the lower end of that scale but it depends on how you operate.

The low-wines are transferred for a second distillation into the feints still. This is where the distiller will begin to select and remove desirable compounds through cuts. The initial spirits to emerge from this distillation are the foreshots, as usual, which will be cut and/or recycled depending on what the distiller wants. The next is called ‘strong feints’, and then finally the ‘weak feints’ (the tails in double distillation). The weak feints are recycled in each batch of low-wines that enter the feints still. So the second distillation is constantly producing a cycle of weak feints that get fed back into the feints still.

The strong feints, which are around 68-72% ABV, go forward to the spirit still for the third and final distillation. Then it all begins again. There are foreshots that the distiller will cut/recycle. In the next run, the distiller will separate the heart, the spirit to be kept and aged, and the strong feints which are recycled into the spirit still during this third distillation. Then there are the weak feints, which, once again, join the low wines in the feints still. The whole process relies on the distiller’s discretion of where to make cuts, from heads to hearts to tails, in the second and third distillation, not just the second distillation as they would in double distillation.

In triple distillation, the heart is concentrated so much that it comes out stronger than it would in double distillation, around 80-85% ABV typically. But when you taste triple-distilled whiskey, you won’t find it any stronger because at this point it still needs to age (where naturally some of the alcohol will evaporate thanks to the angel’s share) and because whiskey is often diluted out of the cask to bottling strength. 

The stills at Teeling Distillery

A trio of stills is a common sight at an Irish distillery. Now you know why.

The magic of three

By adding a third still, you’re both increasing rectification and copper contact. This greater concentration of the alcohol also heightens the lighter, aromatic, fruity flavours like the citrusy, clean character that the terpene oils of barley husk yield. These are readily alcohol soluble, so higher-strength triple-distilled whiskey will have more of them. By removing more of the volatile congeners, you’re also reducing any friction or burn when you drink the spirit, hence why people associate Irish whiskey with being ‘smooth’. 

Triple distillation also gives the distiller more flexibility in where they make their cuts, and what to add back in. When you have multiple mash bills (grain recipes) as you do in Irish whiskey, with malted barley and unmalted barley, as well as other grains like corn or oats being distilled together, that’s going to create a lot of foreshots and feints that the distiller can more easily refine. This greater extraction of alcohol is also useful with a mash of malted and unmalted barley, which tends to be a mix that provides a lower yield of alcohol. 

That’s not to say that triple distillation is necessarily a superior method, it’s about what flavours and textures you want. Oilier, heavier, more complex flavours are more water-soluble, so they can be reduced with triple-distillation. You can leave complexity behind for clarity. This supposedly lighter, fruitier, and ‘smoother’ style is often championed by ambassadors of Irish whiskey as a means to distinguish it from Scotch. This can be a little reductive, however. A light whisky can be harsh. A robust whisky can be smooth. Whisky is full of nuance, and triple distillation is no different.