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About Ageing Rum PART 2: “The Mystique Of Wood”

Ageing Rum wood barrels

The beauty of the universe is its relativity and that’s why nature is not always precise. If you pick two apples from the same tree they will not have the same shape, they will have different shades of color and even can have a slightly different taste. Depending on which side of the tree each apple grew, meaning the sun level each of them had or how much wind exposure in addition to so many other variables. 

With wooden barrels, the same happens. You can build two barrels from the same tree, fill them with the same Rum and store them in the same warehouse one next to the other and yet, you will obtain different Rums. There are so many variables that make ageing a truly mystical process. But, as always, let’s start from the beginning. 

First of all, the producer makes the choice about which barrel type he wants to use. Just as an example, “French Limousin”  will give more astringency to the Rum due to its higher level of tannins (antioxidants) and will take more time to extract tertiary aromas from it due to its high quantity of “rings” in an “inch” measure; “American White Oak” will give to the spirit lots of vanilla and nutty flavors due to its higher level of lignin and low quantity of “rings” in one “inch” measure (which means faster tertiary aromas extraction); “Chestnut” barrels will give more oxidation due to its bigger porosity but also even more astringency than French Oak because of its higher presence of gallic acid (one of two acids that creates tannins). I have seen some recent experiments where two different types of wood were combined creating what they call  “Zebra” casks because of its distinctive color duality. Understanding the nature of the wood, the barrel producers will “charr” or “roast” depending on the temperature used and the time. For example, Bourbon Whiskeys are carbonizing for 20-30 seconds at 350-400ºC charring 4mm of the wooden staves in the inside. Cognac producers are using barrels that have been delicately roasted at low temperatures but for 5 to 18 minutes. During this process, the heat transforms the wooden compounds: carbohydrates are becoming caramel and butterscotch; lignin is becoming vanillin and spices; tannins are being reduced due to the high temperatures giving less astringency and more smoothness. 

In addition to this large range of wood typologies, charring or roasting, there is an infinite world of “used” barrels that give unique flavors to the Rum during the ageing. This technique is called “Finish” and is used to obtain flavors and tastes from the product that was before inside the cask. The product that was previously inside the barrel will strongly influence the Rum profile, especially under high tropical temperatures where the extraction is the highest.If we were able to squeeze a 200 liter ex Bourbon barrel (used before to age Bourbon) like a sponge, we would obtain around 5 liters of Whiskey that stayed inside the wooden cask staves. Of course, it also depends on how large the barrel is. The larger the capacity, the lower the perception of tertiary aromas and the product that was in there before (in case of ageing in used barrels). Au contraire, the smaller the barrel capacity, the higher the extraction of aromas and influence of the previous product. In addition to this, the higher the Rum alcohol % is when they fill the barrels, the faster the extraction and shorter the barrel “life” will be (less years the barrel will give aromas to the liquid). 

If all of this was not already enough, there is another variable other than the climate (which I already explained in my previous article): the barrel position. The upper cask lines near the warehouse roof are under higher temperatures which means even higher “Angel’s Share”, concentration and tertiary aromas extraction. For example, in our Ron Abuelo warehouses in Panama, the lower barrel lines right on the ground are losing annually around 8% “Angel’s Share”. Our upper barrel lines are losing up to 15%. The closer you get to the sky with your barrels, the more the Angels steal from them! 

Almost all rums are using “White American Oak” ex Bourbon barrels. The reason is simple, American whiskeys can only use the cask once! This translates to greater value barrels for aging in the spirit market. American Oak also is more immediate in terms of tertiary aromaa extraction versus French Oak, and definitely cheaper! 

However, nowadays there are many possibilities and different used barrels available. That is why lots of Rums present distinctive “Finishes” in ex Sherry, Port, Cognac or even Grappa among many others to the final customer. It all depends on how much the producers want to invest and which unique Rum profiles they want to launch in the market. Just so you know, a good 500L ex Sherry Oloroso “tonel” costs around 1000-1200$ compared to the American Oak ex Bourbon Type 1 Select which costs 200$. Producing fancy “finishes” costs a considerable amount of money and that is why Rum prices are higher in these cases. 

In my next article, we will talk about the “ageing systems” which will clarify the numbers and labels misunderstandings. Stay tuned and remember: drinking Rum before noon doesn’t mean you have a problem, it means you are a pirate!

Read Chapter 1 in this series: The Three Rum Revolutions And The Beginnings Of Rum
Read Chapter 2 in this series: Rum: The Sugarcane Journey
Read Chapter 3 in this series: Rum: Fermentation Craziness
Read Chapter 4 in this series: Rum: The Distillation Puzzle
Read Chapter 5 in this series: About Ageing Rum PART 1: “Why More Is Not Always Better”