It is always exciting to fill your barrel with a newly distilled batch—once you have grown the habit of aging your own spirits. Or maybe you bought a secondhand barrel at an auction or from a distillery. A dry barrel needs to be cleaned.
This brings us to the question of how you clean the inside of a whiskey barrel.
- Prepare your barrel for cleaning.
- Cleaning the inside of the barrel.
- Rinsing the barrel with clean water is usually enough, but you can also use mild detergent and warm water.
- You will need chemical intervention if your barrel develops an unpleasant smell or shows signs of mold.
- Remember to always rinse your barrel before filling.
There are three basic steps to cleaning the inside of your whiskey barrel. First, prepare and swell the barrel to prevent leaks. Second, rinse the barrel thoroughly, or use chemicals. Lastly, if you will not use your barrel for the foreseeable future, store it correctly.
Preparing Your Barrel for Cleaning
Let’s assume you bought a secondhand barrel. It may contain some leftover liquid (never let a barrel dry out!). In the extreme case where you get a dry barrel, you’ll need to cure it again and clean it.
The first step is to swell the barrel, ensuring it will hold liquid without leaking. It prevents too much oxygen from coming into contact with your contents (in this case, whiskey). You can achieve this in a few easy steps according to the warm water method.
- Fill your barrel with hot water (175°–180°F/79–82ºC) around one-tenth. Never use boiling water.
- Replace the bung and roll your barrel around to make sure the water touches the inside surfaces.
- Turn the barrel upright, again using hot water, and fill the top part of the outside of your barrel. Let it rest for about 15 minutes. Turn the barrel over and repeat the process.
- Fill the barrel with water and check for leaks or seepages. If you notice the barrel leaking or seeping, allow the wood to swell and absorb more water.
- Never leave water in the barrel for over two days because it can encourage microbial and bacterial growth, spoiling your spirits in your barrel to age.
- Empty the barrel and rinse it with clean water three times.
The cold water method takes much longer than the above.
Cleaning the Inside
It’s time to clean your barrel. Keep in mind cleaning the inside will strip away some flavors. There are various methods that you can use, so let’s get cleanin’!
Rinsing your barrel with clean water is one way to ensure the longevity of your barrel. Drain all the (residual) liquor and rinse the barrel until the water runs clear. Easy as that.
A warm water and soap solution can also be used, but be sure to rinse your barrel afterward.
But, if the barrel develops mold, you will need some chemical intervention. Keep in mind with each chemical treatment, you will strip the wood of its flavor properties.
Sodium percarbonate or soda carbonate are the two common cleaning agents used to get rid of bacteria and microbial build-up inside barrels. It is also used to get rid of smells.
The recommended dosage is a tablespoon of either per gallon of water. Roll or swirl the barrel to make sure you cover the inside completely. Again, you will rinse your barrel at least three times, but to be safe, four times.
If mold grows on the outside of your barrel, you can use this solution to wash the outside as well. We would recommend washing the outside regardless—just to be on the safe side.
Other than mold, whiskey fungus (Baudoinia compniacensis) can also grow on the outside of older barrels. Ethanol evaporating from the aging whiskey encourages the growth of whiskey fungus. Distillers referred to it as the angel’s share, but it can wreak havoc as well.
Always be careful when working with chemicals. Wear gloves and protective eye gear. Although these are bases, they can still cause corrosion or splash and hurt you.
An alternative to chemicals is Barrel-Kleen—a biodegradable cleaner for barrels. Be sure to follow the manufacturer’s instructions when mixing the product.
After using Barrel-Kleen, you need to use an acid neutralizer as well. Rather buy the complete Barrel-Kleen cleaning kit, which has everything you need for cleaning and neutralizing.
Storing Your Clean Barrel
If you do not fill your barrel with whiskey immediately, you can store it. However, avoid using sulfur dioxide (SO2) gas (from sulfur discs) for barrels that will age spirits, such as whiskey.
SO2 gas dries the barrel, kills bacteria and microbes, but it also adds sulfides (and sulfites) which penetrate the wood, imparting a sulfur taste to the whiskey. It also dries the barrel, leading to cracks and leaks.
The alternative is to use a citric acid solution inside the barrel. This will prevent bacteria, microbes, and mold from growing inside your barrel. And your barrel will stay moist.
To make this solution, you will need the following:
- 1 teaspoon of citric acid
- 2 teaspoons of potassium metabisulfite per gallon (4 liters) of hot water.
Fill the barrel to the brim with the solution to store your barrel for up to six months. Remember to rinse your barrel thoroughly, let it dry for 3 hours, and then fill it with liquor.
We’ve looked at preparing your barrel by swelling it with hot water first to prevent leaks. After swelling, you need to clean the inside—rinsing three or four times will do the trick. You can also opt for a mild detergent and warm water.
But, if your barrel develops a smell or has mold growing inside, you will need to use chemicals to kill the mold and/or bacteria. Keep in mind, with each chemical treatment, over time, you will lose the barrel’s flavor properties.
Last, storing your barrel correctly will prolong its life and prevent serious interventions before you fill it up again.