The following describes the production process of Irish Pure Pot Still Whiskey, primarily based on the procedures at Midleton Distillery, which is part of Irish Distillers. This distillery produces whiskey for brands like Jameson, Powers, the Spot series, and Redbreast. Currently, Bushmills and Cooley distilleries use production methods similar to those of Scotch single malt whiskey, although Bushmills employs a complex triple distillation process. Additionally, Cooley's brand Connemara, which undergoes double distillation, uses heavily peated barley. Both Irish Distillers and Cooley produce grain whiskey as well.
1. Malted Barley
Although different barley varieties are used, the malting process is similar to that in Scotland, where enzymes are activated to convert starches into sugars. Hot air is used for kilning, without any peat.
2. Unmalted Barley
In the 19th century, a heavy tax was imposed on malted barley, which led many Irish whiskey producers to incorporate a certain proportion of unmalted barley in their grain recipes. The standard ratio is 60:40 (unmalted:malted), though this may vary by brand. This mix of malted and unmalted barley gives Irish Pure Pot Still Whiskey its unique spicy/apple flavor and enhances its rich, oily texture.
3. Brewing
The malted and unmalted barley are wet-milled separately before the resulting grist is transferred to the mash tun. The two types of barley are mashed together in a 1:2 ratio, with the temperature gradually increasing from 55°C to 75°C to ensure full conversion.
3.1 Lauter Mash Option 1
After mashing, the liquid is transferred to a lauter tun to extract the wort. Only the high-sugar "strong wort" is collected for fermentation. After filtering, water is added, and the "weak wort" is retained to be used as water in the next mash, with clear wort being collected.
3.2 Mash Filtering Option 2
This mash filtering method effectively extracts sugars from the wort. A hammer mill crushes the malted barley and unmalted barley into fine grist, which is then mixed and transferred into the mash tun. The wort is then processed through a large filter with 86 plates. Each plate has perforations on one side, and as the wort is pumped between the plates, pressure forces it through the plates, leaving behind solid residue. Pressure is increased to extract all fermentable sugars, and the liquid is then divided into strong wort and weak wort.
4. Fermentation
Distillers’ yeast is added, and fermentation lasts at least 60 hours, with the option to extend it up to 120 hours. The collected fermented liquid has an alcohol content of 9-10% ABV.
5. Distillation 1
All Irish Pure Pot Still Whiskey is distilled three times, and distilleries typically use four pot stills of the same size and shape. The first distillation takes place in two wash stills, and the collected low wines have an alcohol content between 25% ABV (for heavier styles of Pure Pot Still Whiskey) and 40% ABV (for lighter styles).
6. Distillation 2
The low wines and weak feints are redistilled in a feints still. The distillate is separated into three parts: heads, hearts, and tails. The heads and tails are collected in the weak feints receiver, while the hearts are collected in the strong feints receiver. By adjusting the cut points of the distillate, different flavors can be retained or removed. The lower the strength of the hearts, the heavier the resulting spirit; the higher the strength, the lighter the spirit.
7. Distillation 3
Once again, the distillate is split into three parts. The heads are collected as strong feints, the hearts are collected for maturation, and the tails are divided into two parts: the first part goes to the strong feints receiver, and the second part goes to the weak feints receiver. Different cut points also create different characteristics.
7.1 Column Distillation Option 1
The residual alcohol left in the three pot stills is transferred to two column stills, where "column feints" are distilled. These feints can be used in subsequent pot distillation to create specific styles.
7.2 Column Distillation Option 2
Although Pure Pot Still Whiskey does not use column distillation, distillers may choose to divert the distillate into a column still at any point to provide more options when blending whiskey. Some distilleries also produce 100% column-distilled grain whiskey, based on corn, or malted barley grain whiskey.
8. Maturation
A wide variety of oak casks are used for maturation, many of which are custom-made, including sherry casks, port casks, and Madeira casks. Most new spirits are aged in first-fill casks.