What Is Irish Whiskey?

When it comes to whiskey from the European continent, Scotch might get all of the limelight but Ireland has a lovely and delicious distilling culture of its own. Irish whiskey borrows a number of components from the Scottish tradition, but (as you might expect from that rebellious bunch) they put their own spin on things to make it their own.


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The legal definitions of Irish whiskey are much less strict than their Scottish counterparts, but that doesn’t mean that it’s the wild west.

Raw Materials

Right off the bat, there is a huge difference between Irish and Scottish whiskey when it comes to the raw materials used. With the Scottish tradition, all of the barley used in the production of their spirits typically goes through the malting process. But with Irish whiskey, there’s a proud tradition of using unmalted barley in the process as well, something that adds some unique flavors.

For the malted barley, the grains are first soaked in water and then laid out in a malting room for some period of time while the seeds inside the barley start to germinate.

There’s a very important reason for this germination. Seeds are made up of complex carbohydrates, which are intended to be used as food for the new plant. But plants (and yeast, for that matter) can’t directly use carbohydrates — it needs to be broken down into simple sugars for the plant first in a process called “enzymatic hydrolysis”. When the new seed germinates, it releases natural enzymes that break down the complex carbohydrates into simple sugars that it can then use.

For Scotch whisky, only natural enzymes are allowed to be used to convert complex carbs into sugar. Which is why you’ll see malted barley used fairly exclusively. Irish whiskey is different in that commercial enzymes are allowed to be used in this process, which means you can see things like 100% unmalted barley or even grain whiskey that has no barley whatsoever.

The trick with malting barley is that we want the germination to happen, but we don’t want the new plant to eat all of the available sugar. That sugar is what our yeast is going to eat and turn into alcohol, so we need the barley to stop growing at some point. This is accomplished by heating or “kilning” the malted barley which raises the temperature of the seed and stops it from growing any further. Most malting facilities will use a clean modern source of heat such as natural gas, but the traditional method of heating the barley is with peat — a natural fuel that creates a distinctive smoky aroma. Some distilleries still use peat smoke during the kilning process to impart that smoky flavor into their spirit.

Irish Malt Whiskey requires that 100% of the grains used for the whiskey need to be malted barley.

For Irish Pot Still Whiskey, 30% of the grains used in the process need to be malted barley, and 30% need to be UN-malted barley. You can use more (like a 50/50 split) but that’s the minimum.

The wildcard here is Irish Grain Whiskey, which only really stipulates that a maximum of 30% malted barley can be used. You can go as low as zero percent in this category, with corn usually replacing the barley.

For grains other than malted barley, they are typically milled or crushed and then cooked in a warm bath before moving to the next step.

Fermentation

Now that we have a soup of sugary liquid and grain remnants, it’s time to start the fermentation process. This is where yeast (a single cell organism) eats the sugar in the solution and produces ethanol (alcohol), carbon dioxide, and heat.

Typically distillers will use cultured, lab grown yeast for their fermentation process. These cultured yeasts are grown and selected for their ability to create alcohol and for their specific flavor profiles, ensuring that the flavors are consistent from one distillation run to the next, but there is no restriction on using wild (ambient) yeast for distillers.

Fermentation will typically take a couple days and, once complete, the fermented liquid (called the “wort”) is drained from the tank. Typically, distillers will spray down the remaining solid matter in the tank to make sure all of the available alcohol has been extracted (called “sparging”).

Distillation

Irish whiskey seems to constantly be one-upping their English counterparts. In Scotland, spirits are typically distilled twice, but in Ireland the common process is distilling them three times in pot stills. These stills are usually constructed from copper, which is a component that reacts with the vapor and liquid in the still to remove unpleasant sulfur compounds that taste pretty awful. The vapor produced in the still is commonly cooled in a “shell and tube” condenser, which is where pipes containing the hot gasses are cooled by a water jacket to force them to condense back into a liquid. This container is also usually made out of copper for additional sulfur reduction.

In the first distillation, the primary focus is to strip out all of the water from the wort that resulted from the fermentation process. This is sometimes called a “stripping run”, and if a dedicated still is used it’s called a “wash still”. There isn’t excessive care or attention paid to isolating out specific components at this point, and the results are called “low wines”, as they have a lower alcoholic content than the final product. What’s left in the pot is called “pot ale” and is discarded.

The low wines are then put into a charging vessel, some other components from the second distillation are added (we’ll get to that in a second) along with some water to reduce the overall alcohol content in the mixture. This process causes some of the less desirable components (fusel oils) to fall out of solution and get stripped off before the mixture is added to the second still.

In Irish triple distillation, the middle still is called a “feints still” because the output here is “strong feints” (which are passed along to another charging vessel for the final distillation) and the “weak feints” are left in the pot at the end of the distillation run. These weak feints are added back to the charging vessel from the first distillation run as they still contain some alcohol and some good flavors that we’d like to try and extract.

The final distillation (typically in a “spirits still”) is closely monitored. The first thing that comes out of the still is called the “heads” of the distillation run and it mostly contains highly volatile materials with a lower boiling point, things like solvents and other nasty components. At some point, the distiller decides that the heads are finished and what’s coming out of the still is the spirit they want to capture (called the “hearts”) and they start capturing that liquid into barrels. When all of the alcohol they want to capture has been extracted from the liquid, they make one more “cut” to stop barreling the spirit and they let the rest of the mixture (called the “tails”) flow until the stream of liquid stops.

These two unwanted cuts — the heads and the tails — are called “pot feints” and are added back to the charging vessel for the next distillation run. What’s leftover in the pot from the final distillation is discarded.

Not all Irish whisky uses a pot still for their production, though. In fact, the prevalence of column stills used in the country is another differentiating factor between them and the Scots. A column still or a “continuous still” is commonly used in Irish grain whisky, whereas pot stills are usually more common for Irish malt-based whiskey (and, in the case of “Irish Pot Still Whiskey”, is actually a legal requirement). But in either case, the legal maximum alcohol content for the spirit that they create is 94.8% alcohol by volume.


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Maturation

Once the whiskey has been created, by law it must be aged in oak vessels (less than 700 liters in size) for a minimum of three years. There are a lot of options here, especially since European whiskey doesn’t have the same requirement as American bourbon to use a new barrel every time. In fact, the majority of barrels used for scotch maturation are previously used American bourbon barrels that have been disassembled and re-constructed to the distiller’s specifications.

Different distillers will have different opinions on the best way to age their spirits, though. Some will use American oak, others European oak. Some will only age a short period of time, while others will let their whiskey rest for decades. And the choice of location for the warehouse also has a huge impact on the final product, with hotter climates having a more pronounced impact than cooler climates. By law, though, 100% of this aging needs to take place on the Emerald Isle itself to call itself Irish whiskey.

Bottling

Once the spirit has been aged, it is finally time to bottle. In general, most Irish whiskey will be a blend of multiple different barrels to get the right flavor profile. By law, the only thing allowed to be added to the spirit is water (for proofing the spirit to the right alcohol content) and caramel coloring (specifically E150A caramel coloring).

  • Irish Pot Still Whiskey is a pot distilled spirit that must have at a minimum 30% malted barley and 30% unmalted barley as part of its grain bill.
  • Irish Malt Whiskey is a pot distilled spirit that comes from 100% malted barley.
  • Irish Grain Whiskey is a distilled spirit where the grain bill must include no more than 30% malted barley.
  • Irish Blended Whiskey is a blend of two or more types of Irish whiskey.

The bottle of whiskey must have a minimum of 40% alcohol by volume (ABV) and a maximum of 94.8% ABV to meet legal requirements.

Hopefully you’re walking away from this with a slightly improved understanding of Irish whiskey. And too keep learning, it’s time to start trying out the different varieties and find a favorite! Even with all the requirements there is still plenty of variation and choices for distillers to make, meaning you can always find something unique and interesting in just about every brand you try. Check out our full list of reviews here — and happy exploring!


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