Warehouses for whiskies

Dunnage is the most traditional warehouse, with stone walls and a slate roof. Often placed beside malt whiskies, the dunnage provides stable and cool temperatures thanks to its thick stone walls and slate roofs that minimize temperature changes. Earthen floors enhance humidity, and windows or vents provide air flow. Casks are typically stacked three high on racks, meaning they all experience the same conditions.

Rickhouses are modern structures made typically of concrete or metal with metal roofs. They are usually positioned on hilltops or in open countryside. Also known as "racked warehouses" in Scotland and "rickhouses" in Kentucky, these warehouses store barrels of Bourbon on tall racks, up to 20-25 barrels high. The temperature in summer can reach up to 38°C (100°F), while in the rickhouse, the temperature is around 24°C (75°F) on the ground floor and rising to 46-49°C at higher levels. The position of a barrel in this warehouse is crucial because the ground floor has higher humidity, which means it loses more alcohol than water through evaporation. Meanwhile, the upper levels are drier, and more water than alcohol evaporates, leading to an increase in alcoholic strength and more intense spice. In the past, barrels were rotated in the rickhouse to compensate for differences in temperature and humidity at different levels, ensuring that the whisky aged uniformly. Nowadays, the common approach is to blend barrels from different levels to achieve a uniform and consistent final product, regardless of where they were aged in the rickhouse.

Palletized warehouses are modern, large, tall structures made of brick or metal and come with varying degrees of insulation. They are called palletized because casks are stored vertically on pallets, unlike dunnage and rickhouses, where casks are stored horizontally on racks. This vertical storage maximizes space but raises questions about whether and to what extent it influences the aging process. Over time, the volume of liquid in the cask gradually decreases. As a result, the maturing whisky is in contact with different parts of the cask when stored vertically compared to horizontal storage. Ongoing research is being conducted to compare the effects of the two storage options.