When you are sipping on that delicious whiskey do you ever wonder where the amazing taste comes from? A lot of people will say “the grains” or “the craft and care from the master distiller” While these things are true, did you know that the flavor of whiskey is largely influenced by the wood in which it’s aged? The type of wooden barrel, the size of that barrel, and the amount of time the whiskey spends in the barrel all play a role in the final taste. In fact, up to 70% of the flavor of whiskey comes from barrel aging and 100% of the color comes from the barrel. So grab your favorite wood flavored drink while we explore the science behind barrel-aging and how it affects the flavor of whiskey.

Types of Whiskey Barrels:

Whiskey Barrels Aging

There are two main types of barrels used for aging whiskey: American oak cask and European oak cask. American oak barrels are made from white oak and are typically charred on the inside to give whiskey a caramel, vanilla, and coconut flavor. 


European oak barrels, on the other hand, are made from a variety of oak species and are not typically charred. These barrels give whiskey a more subtle, spicy flavor with hints of dried fruit and nuts.

In addition to American and European oak barrels, Japanese oak barrels are also gaining popularity in the whiskey industry. These barrels, known as Mizunara oak, are made from the rare Japanese oak tree and are prized for their unique flavor profile. Mizunara oak barrels can impart flavors of sandalwood, incense, and spice to whiskey, making them a sought-after choice for whiskey makers. However, Japanese oak barrels are also notoriously difficult to work with and can be expensive, which means that Mizunara-aged whiskeys tend to be pricier than their American or European counterparts.

The toasting of whiskey barrels:

Toasting is a crucial step in the barrel-making process that can have a significant impact on the flavor and visual color of the whiskey. During toasting, the inside of the barrel is exposed to a flame, which caramelizes the natural sugars in the wood and gives the whiskey a deeper, richer flavor. The length of time the barrel is toasted, as well as the intensity of the flame, can impact the final flavor profile of the whiskey.

Toasting can also impact the visual color of the whiskey. Whiskey that has been aged in heavily toasted barrels tends to have a darker, reddish hue, while whiskey aged in lightly toasted barrels tends to be lighter in color. The level of toasting can also impact the mouthfeel of the whiskey, with heavier toasting resulting in a thicker, creamier texture. 

There are typically three levels of toast (who knew toast was so exciting?)

Light Toast
Medium Toast
Heavy Toast

Light toast: During a light toast, the barrel is only toasted for a short period of time, typically around 20 minutes. This style of toasting is typically reserved for whiskey that is a bit more mild.

Medium toast: A toasting that lasts slightly longer than a light toast, normally around 20-30 minutes. This will result in whiskey with a bit more color development and a stronger flavor profile than a light toast. 

Heavy toast: The kind of toasting most whiskey fans prefer (at least the whiskey fans here at Distillery Dudes). A heavy toast lasts around 30-40 minutes and will give you a maximum flavor and a beautiful color on your whiskey. 

What is the difference between toasting and charring a whiksey barrel?

Toasting is a lighter process compared to charring barrels. Charring is a more intense process that involves setting the inside of the barrel on fire to create a layer of charred wood called “alligator char.” This process gives the whiskey a smoky, charred flavor and also helps filter out impurities. The level of charring can vary, with different levels producing different flavors.

There are different levels of charring, which are conveniently referred to as “char levels.” The char level is determined by the length of time the inside of the barrel is exposed to flame and the intensity of the flame. The most common char levels are:

Char Level 1

Char Level 1: Also known as “light char,” this involves exposing the inside of the barrel to flame for about 15 seconds. This produces a thin layer of char that imparts a light smoky flavor to the whiskey.

Char Level 2

Char Level 2: This is also known as “medium char” and involves exposing the inside of the barrel to flame for about 30 seconds. This produces a thicker layer of char than Char Level 1, which results in a more pronounced smoky flavor in the finished whiskey.

Char Level 3

Char Level 3: This is also known as “heavy char” and involves exposing the inside of the barrel to flame for about 45 seconds. This produces a very thick layer of char that imparts a strong smoky flavor to the whiskey.

Char Level 4

Char Level 4: This is the highest level of char and is also known as “alligator char.” It involves exposing the inside of the barrel to flame for about a minute or more, which creates a deep, alligator-like texture on the surface of the wood. Alligator char is the most intense level of char and imparts a very strong smoky flavor to the whiskey.

If you ever get to go to a cooperage and witness the charing process in person, we highly recommend it. It will give you a deeper appreciation for the skill and art that goes into the whole whiskey making process. The char level used by a distiller can have a significant impact on the flavor profile of the finished whiskey, so it is an important decision, and one we are very thankful for, in the barrel-making process.

The Aging process of whiskey:

Ready for a bit of science talk? Good because we can’t talk about whisky aging without talking a little science. The best things in life are worth waiting for (a great talk track for all those ring shy boyfriends out there) and whiskey is no exception. Whiskey aging is a complex and critical process that involves multiple chemical reactions occurring inside the barrel. As the whiskey is stored in the barrel, it slowly begins to take on the unique flavors and colors that we associate with quality whiskey. During the aging process, the whiskey absorbs various compounds from the wood, such as tannins, lignin, and wood sugars, which contribute to the final flavor profile of the spirit. Additionally, as the whiskey interacts with the charred interior of the barrel, it undergoes a process known as oxidation, which can impart additional flavors and colors to the whiskey.

The aging process can take anywhere from a few months(way too short) to several years, and during this time, the whiskey will gradually lose volume due to evaporation. This lost volume is commonly referred to as the “angel’s share” and can range from 2% to 10% of the total volume of the whiskey. As the whiskey loses volume, it becomes more concentrated, which can result in a stronger, more intense flavor profile. However, too much evaporation can lead to a loss of flavor and an overly oaky taste.

The color of the whiskey can also change significantly during the aging process. When whiskey is first distilled, it is clear and colorless, but as it is aged in the barrel, it takes on that rich, amber hue we all adore. This color change is due to the whiskey interacting with the charred interior of the barrel and absorbing compounds such as vanillin and caramel from the wood. The longer the whiskey is aged in the barrel, the darker and more complex its color will become.

Whiskey Color- Amber Hue

In addition to the aging process itself, the type of barrel used for aging can also have a significant impact on the final flavor profile of the whiskey. For example, American whiskey is often aged in new American white oak barrels that have been charred on the inside, which imparts a smoky, oaky flavor to the spirit. Bourbon barrels must be new charred oak barrels and bourbon must be aged in these new oak barrels two years. Scotch whisky, on the other hand, is typically aged in used barrels that have previously held bourbon or sherry, which can result in a more complex, layered flavor profile.

Overall, the whiskey aging process is a crucial step in the production of barrel-aged spirits, and it can significantly impact the final flavor and color of the whiskey. From the type of barrel used to the length of aging time and evaporation, there are many factors that distillers must consider when creating their own unique spirits. For connoisseurs, the aging process is an integral part of the whiskey experience, and there is no substitute for the unique flavor profile that can only be achieved through proper barrel aging.

The Impact of temperature and humidty during the aging process:

Temperature and humidity are also crucial factors in the aging of whiskey. The barrels are often stored in warehouses that are not climate-controlled, which means that the whiskey is exposed to the elements. As the temperature and humidity change throughout the year, the whiskey expands and contracts, causing it to interact with the wood of the barrel differently. Many distillers believe that rotating barrels throughout the aging process allows for a more even interaction between the whiskey and the wood, while others believe that leaving the barrels in the same spot throughout the aging process produces a more complex and nuanced flavor profile.

Whiskey Barrel- Angle Share

The impact of temperature and humidity on the flavor and aging of whiskey cannot be overstated. Heat causes the whiskey to expand and push out through the wood, allowing it to pick up flavors from the oak barrel. Humidity, on the other hand, affects the rate of evaporation and the amount of “angel’s share,” or the amount of whiskey that evaporates during the aging process. The angel’s share can vary depending on the climate of the warehouse, with more evaporation in hot, dry climates and less evaporation in cooler, more humid climates.

Furthermore, temperature and humidity also affect the color of the whiskey. The longer the whiskey ages, the darker it becomes as it absorbs color from the wood. Warmer temperatures and higher humidity levels can speed up this process, resulting in a darker whiskey in a shorter amount of time.


If you like whiskey then you should be thankful for wood, more specifically wooden barrels. Barrel-aging is a complex and fascinating process that plays a crucial role in the flavor of whiskey. The type of wood, the size of the barrel, and the amount of time the whiskey spends in the barrel all impact the final taste. By understanding the science behind barrel-aging, whiskey enthusiasts can gain a deeper appreciation for the complexities of their favorite drink.