Cask Management in the Warehouse

How do the seasons affect maturation?

Summer has just arrived so I wanted to take this chance to write about a more nuanced element of cask ownership – bonded warehousing. A warehouse might sound incredibly boring, so I would recommend an Irish coffee to help you through this.

Maturation in casks is influenced by the seasons. Unlike wine, I am not referring to the sweetness/fruitiness of the raw ingredient, but instead spirit/whisky in the cask and how from Winter to Summer the pace of maturation changes.

I don’t want to spark any arguments, so first, a disclaimer – there are no right or wrong answers when it comes to maturation. Sadly, peer-reviewed studies on maturation environments are few and far between. Here in Scotland, we have been making whisky almost the same way for centuries – definitely since 1494, maybe even from the late 1300s (not the best record keepers I will admit – thankfully we have monks).

Thanks to the success of trial and error, modern science has rarely turned its eye toward whisky.

When it comes to seasons and weather the theory is simple: the hotter weather forces whisky in the cask expands and has a higher liquid-to-wood contact ratio, resulting in more oils & tannins being imparted into the whisky. With this expansion in Summer months generally, more flavour will be gained as opposed to the cooler winter. Luckily with Scottish summers, as you can imagine, this isn’t a dramatic shift. Kentucky for example faces very different seasonal changes in their Bourbon. 

Humidity is a far more polarising topic, this could be an entire standalone article. At a glance, high humidity increases the evaporation of ethyl-alcohol, whereas low humidity forces higher evaporation of the water content within the cask. There are stories of some casks in the right climate having their ABV go up!

These two influences left unchecked would either create dramatic flavours in the spirit or very little change at all. Where seasonal swings are important for a balanced maturation, consistency is key.

The importance of the bonded warehouse

This is where bonded warehousing plays a crucial role. Every cask in Scotland has to be stored in an HMRC government-bonded warehouse until duty is paid, typically when the whisky enters a bottle.

These warehouses are not your average shed. Traditional warehouses have stone walls thicker than 1m, dirt floors (for cooling/dampness), and mesh/barred windows to allow airflow.

With this, the seasonal effects of humidity and temperature are slightly muted. Keeping the temperature and humidity within a consistent range year-round.

Modern warehouses achieve a similar effect with ventilation systems and a two-wall structure with a cavity between.

The three kinds of warehouses in Scotland

There are three commonly used types of warehousing: palletised, racking, and dunnage.

  1. Palletised: Modern and space efficient, not a style we typically use here at Braeburn. Casks are stored upright on a pallet up to 8-10 pallets high. Scotland is a small country with warehouse space being short; this latest iteration of bonded warehousing was a clear next step for the industry.  
  2. Racking: Modern combined with traditional, racking always reminds me of the capsule hotels in our world’s megacities, innovative and space focused. With racking you have rows and rows of casks supported by a framework allowing the casks to be stored as high as the structure can support.
  3. Lastly, Dunnage: this is our most common method of storage, the vast majority of casks under Braeburn’s management are stored in this traditional style. Casks are stored in rows only three high, as they are rolled into place by hand. Dunnage is easily accessible, although very inefficient and is by far the most romantic.

I will stop myself here before this tangent carries on any longer.

Thank you for taking the time to read and should you have any questions, I am always happy to discuss anything whisky.

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