Malt Irish whiskey is produced from malted barley distilled either two or three times in a pot still. Pot still Irish whiskey is produced from a combination of malted and unmalted barley, and distilled in a pot still (typically) three times. These differences promote two distinct styles of whiskey, and together with other vital factors such as the choice of casks and length of aging, each distillery also has its own individual house style.The tradition of using unmalted barley to produce pot still Irish whiskey began in the 18th century, prompted by the introduction of a tax on malted barley.Consequently, adding some unmalted barley enabled distillers to use less malted barley, and therefore reduce their tax liability.The proportions of malted to unmalted barley vary, which promotes different styles of spirit (regulations stipulate a minimum of 30 per cent malted barley). Including some malted barley is of course essential, as the process of malting the barley (ie. allowing it to germinate) also triggers the release of enzymes, which perform a vital role during mashing, driving the conversion of starches in the barley into sugars."Higher proportions of malted barley typically result in more prominent malty, biscuity notes. Higher proportions of unmalted barley promote more fruity notes, while also giving the whiskey a more creamy mouthfeel, and a mouth-coating finish compared to the relatively drier finish of malt whiskey. We can accentuate these differences through distillation techniques, and ultimately distillation has a bigger impact on the character of the whiskey than the proportions of malted and unmalted barley," says David Quinn, master of whisky science at Irish Distillers, which produces a range of pot still Irish whiskeys.Triple distilling means using a set of stills each dedicated to one particular distillation, with the first distillation in a wash still, the second in a feints still and the third in a spirit still.The wash still is charged with the wash which has an alcoholic strength of around 8-10% ABV. Once distilled this results in low wines with a strength of around 25% ABV, or higher.Distilling the low wines in the feints still entails three distinct phases. The first and final phases, known as the heads and tails respectively, are of an unsuitable character and quality, and are collected to be redistilled in the next distillation run within the feints still. The middle phase of the distillation run, known as the 'spirit cut,' is collected separately, and has an alcoholic strength of around 70% ABV. This distillate, known as strong feints, typically has a mix of fruit and cereal notes.When the strong feints are distilled for a third time the same selection procedure applies, with the heads and tails collected separately to be redistilled in the next distillation run within the spirit still. The middle phase of the distillation run yields another 'spirit cut,' which is collected separately as new make spirit (that will be matured into whiskey). This typically has a strength of around 80% ABV, or more, and the higher the strength the greater the proportion of lighter notes and the lower the proportion of richer, heavier notes. Even a difference of 1% ABV either way in the strength of the new make spirit influences these proportions, and the character of the new make spirit."The second and third distillations essentially mean taking a spirit cut out of a spirit cut, allowing us to select the characteristics we wish to keep and those we wish to remove, and progressively refining the spectrum into a fruity, floral, spicy character, which defines pot still Irish whiskey. Triple distillation also gives us more opportunities than double distillation, enabling us to make a range of individual pot still Irish whiskeys, depending on the proportions of malted and unmalted barley used, together with different spirit cuts," says David Quinn.Another vital consideration when triple distilling and producing a relatively more delicate spirit is the type of cask used for aging. These are either casks previously used to age bourbon (which contribute vanilla sweetness, among other notes) or sherry (adding for example a richer, dried fruit sweetness).Additionally, different 'fills' of each type of cask are used, with 'first fill' indicating a cask used to age whiskey for the first time, while 'second fill' indicates a second use, and so on.Each time the cask is filled, the influence of the cask on the maturing whiskey is less intense, which means that selecting the fill is a significant factor."We must be very careful with the cask selection, as potentially the influence of the cask can show more clearly with a more delicate spirit. So, we choose casks that will give the desired character. For example, we use first fill casks to give a rich, rounder style of whiskey, and for a more delicate result we use either second or third fill casks," says Colum Egan, master distiller of Bushmills, with Bushmills malt Irish whiskey being triple distilled from malted barley.