About barrel-aged mead

The other day, we held an event at ANTELOPE where we prepared mangoes and learned about barrel-aging mead.

I have compiled a more detailed explanation of barrel-aging, including topics we didn't have time to cover during the event.

I’ve written this in a rather informal style, but essentially, it boils down to the fact that there is still very little information available about barrel-aging mead and many unknowns remain, so let’s all work together to build up the mead scene.

〈Table of Contents〉

1. Basics of Barrel-Aging

- Aging of Alcohol

- Oxidative and Reductive Aging

- Reduction Odors and Sunlight

2. Types of Barrels

⚫︎Wood

- Oak

- Other Woods

⚫︎Size

⚫︎Toast

⚫︎Used Barrels

3. What Happens Inside a Barrel

- Components Extracted from Oak

- Microorganisms

- Accelerating Aging

4. Barrel-Aging Mead

- Oxidation of Mead

1. Basics of Barrel-Aging

Barrel-aging refers to the process of aging alcohol in wooden barrels.

Aging adds aroma and flavor, and softens the alcohol over time.
It can also change the color and add depth to the taste.

Aging of Alcohol

What is aging, in the first place?
Most people have an image of the harshness of alcohol fading away to become mellow over the passage of time.

While this is not actually wrong, the full picture of aging has not yet been fully explained.

One common theory is that alcohol and water are not mixed at a molecular level, and that they blend together as time passes.

On the other hand, there is research suggesting that time itself is not necessary for aging; rather, components like organic acids and polyphenols act to strengthen the hydrogen bonds between alcohol and water, making them indistinguishable (eliminating the burning sensation).

In other words, while aging does occur in bottles and stainless steel tanks, it is likely to progress more efficiently in wooden barrels, which contain higher levels of components like polyphenols.
Furthermore, as wood barrels are used repeatedly, their extractable components diminish, and since used barrels already have components extracted from previous contents like wine, new barrels or sherry casks are more effective for aging.

Oxidative and Reductive Aging

Another major difference between bottles/stainless tanks and wooden barrels is whether the liquid comes into contact with oxygen.

Because barrels are made of wood, oxygen comes into contact with the liquid through the grain.
Conversely, in bottles or stainless steel tanks, you can prevent oxygen contact by filling them with CO2 or similar gases.

So, how do these types of aging differ?

Oxidative aging seeks "umami, depth, and complexity," and is a world of enjoying unique flavors (nutty, caramel, and aged aromas).

Reductive aging is a style that preserves "freshness, purity, and drinkability," delivering the charm of the fruit as is.

While both methods have their own merits, aging can also progress in a negative direction—that is, if it becomes too oxidative or too reductive.
I have compared the deterioration of each.

When it comes to mead, I rarely feel it suffers from oxidative deterioration.
This is likely because mead contains fewer polyphenols—which are highly susceptible to oxidation—compared to wine.
Therefore, it’s quite common for it to remain largely unchanged even two weeks after opening.

Reduction Odors and Sunlight

Conversely, I want to be cautious about reduction odors.
I believe this is also related to off-flavors caused by sunlight.

Specifically, if the self-decomposition (autolysis) of yeast settled at the bottom of the bottle progresses in a reductive state, substances called mercaptans are generated.
What are mercaptans? They are the cause of that specific odor found in dental plaque.
Since these substances are also generated by ultraviolet light, the product will deteriorate rapidly if the bottle is exposed to direct sunlight.

Because I often notice this deterioration due to sunlight, I want to prevent it by using light-blocking bottles and being careful about storage methods.

2. Types of Barrels

First, a bit of history.
Wine production dates back to 5000 BC.
Around that time, fermentation and aging were carried out in clay containers called amphorae.

However, because they were fragile and heavy, barrels were developed.
Barrels were originally used for transporting all sorts of things on ships, not just for aging wine, so using them solely for aging alcohol is a relatively recent practice.

From here, I would like to look at barrels from various perspectives.

Wood

Barrels are almost always made of oak, but not exclusively.
Research observing wine aging using various woods has shown that wood affects 41 types of wine aromas, and 11 of those exist only depending on the type of wood used.

Oak

Oak has many characteristics suitable for barrel aging.
First, because it grows relatively slowly, the grain is dense, providing high strength and water resistance.
Also, unlike other woods, in the late stages of growth, a substance called tyloses blocks the sap channels, preventing liquid from penetrating the wood.

There are two representative types of oak: American and French.
Let's look at the characteristics of each.

• American Oak

• Originates in the US, but the specific region is rarely mentioned

• Coarse grain makes it easier to impart aroma

• Easier to split and process

• Relatively inexpensive

• French Oak

• Includes terroir elements, such as the specific French region of growth

• Fine grain means it imparts aroma more slowly

• High in tannins

• Harder, making it more difficult to process

• Quite expensive

Because French oak has a finer grain, aging in it takes longer, but it can be reused more often.

Other Woods

• Acacia

• Used in Austria for white wine and brandy.

• Lacks the sweet or rich flavor and aroma of toasted oak, but provides tannin and body.

• Chestnut

• Oak originated from chestnut trees.

• Cheaper than oak, also used in the production of Lambic.

• More tannic than oak and has lower water resistance.

• Cedar

• Used for fermentation and aging of Japanese sake.

• Resinous.

• Hinoki (Japanese Cypress)

• Degreased and used as a saccharification, fermentation, and storage vessel.

Beyond these, juniper and walnut wood have also been used; the changes in taste and aroma from different woods seem very interesting.

Size

While there are global standard barrels, countless sizes and types exist depending on the application.
Even in France's two major wine regions, Burgundy and Bordeaux, standard barrel sizes differ (228 liters and 225 liters, respectively), and there are major differences in shape and toasting treatment.

I will introduce the representative ones.

• Barrel (190L) - Used in the American whiskey and bourbon industry.

• Barrique (225L) - The global standard in the wine world.

• Butt (490L) - Used in whiskey production to provide more mellowness and sweetness.

• Fuder (1000L) - Suitable for very gentle aging.

The most important thing regarding barrel size is the relationship between the surface area in contact with the liquid.
In smaller barrels, the surface area in contact with the liquid as a whole is larger, so the extraction speed of components is faster, and the oxygen transmission rate is higher.
In other words, aging proceeds faster in smaller barrels, and slower in larger ones.

Toast

Toasting is the process of burning the inside of an oak barrel with an open flame.
While it is a process to make the wood easier to work with, it also has a significant impact on the flavor and aroma provided by barrel aging.

Depending on the level of char, they are categorized as light, medium, and heavy toast.

Applying heat to oak causes various chemical changes.
I'll explain this in more detail later, but for bourbon barrels, there is a process called "charring," where the surface is carbonized in a short time with an even stronger flame.
This creates a much more intense, sweet, and fragrant aroma.

Used Barrels

Barrels that have never been used before are called "new barrels."
The influence of new barrels is so strong that some winemakers put wine they don't intend to sell into them first to "break them in."

However, if you are attempting to barrel-age mead, you will rarely have the opportunity to use new barrels.
In most cases, you will use barrels that previously held wine or whiskey.

Two things are important here:
- First, with each use of a barrel, the extraction of wood-derived components like polyphenols decreases significantly.
- Second, the liquid will be influenced by the flavors and aromas of whatever was in the barrel previously.

So, what kind of barrels are available?

Among these, the ones I have actually used are wine barrels (red/white) and bourbon barrels.
My impression is that red wine barrels definitely impart tannins and a red wine flavor, while white wine barrels are weaker in woodiness and add a more "woody" flavor. Bourbon barrels, as expected, easily impart rich vanilla and toast notes.

3. What Happens Inside a Barrel

From here, let's look at the phenomena occurring inside a barrel.

As touched upon in the basics, the following are thought to be occurring inside the barrel:

• Strengthening of hydrogen bonds between alcohol and water

• Oxidation reactions

• Extraction of wood components

• Microorganisms

Let's look in detail at the wood components I haven't mentioned yet.

Components Extracted from Oak

• Vanillin

• The most famous component of barrel aroma, created as a result of lignin decomposition due to toasting. It literally smells like vanilla.

• Tannin

• Provides astringency and also plays a role in stabilizing oxidation.

• Lactones

• Said to have the aroma of coconut. Derived from lipids contained in the wood, it is a characteristic component of bourbon.

• Furfural

• A caramel and almond-like aroma. It is produced when hemicellulose is broken down by toasting.

Many other components are also extracted from wood.
Many are affected by toasting; as hemicellulose and other components break down into sugars, the Maillard reaction proceeds, resulting in a caramel-like flavor.

Additionally, the impact on flavor from the liquid previously held in the oak, which has soaked into the wood and is then extracted, is significant.
In a standard barrel, it is said that 2–4 liters of wine are absorbed into the barrel over several weeks, accounting for approximately 1% of the liquid carried over to the next batch.

Basically, the higher the temperature, the greater the impact on flavor.

Microorganisms

Permeability to oxygen means there is a possibility of contamination by microorganisms such as acetic acid bacteria.

Furthermore, yeasts like Brettanomyces can propagate even in anaerobic conditions.
While some production methods take advantage of this, it is generally considered undesirable in worlds like winemaking.

Therefore, in terms of preventing spoilage and the growth of harmful microorganisms, the addition of sulfur dioxide is the most widely used method to prevent not only excessive oxidation but also spoilage by microorganisms.

Accelerating Aging

So far, I have discussed barrel aging, but there is research into various methods to advance aging without using barrels.

The simplest is to use wood chips or immerse a portion of a barrel.
This increases the surface area where the liquid comes into contact with the wood, allowing for faster extraction of wood components.

Beyond this, though I will not explain them in detail, there are many scientific approaches such as the use of ultrasound, micro-oxygenation, pulsed electric fields, high hydrostatic pressure, and microwave or gamma-ray irradiation, which may enable higher quality aging in a shorter period of time.

4. Barrel Aging Mead

From here on, I will talk about barrel aging mead based on experience.
I say "based on experience" because there is little literature that explains mead aging in detail.

Even in "The Complete Meadmaker," a book by Ken Schramm, the boss of the mead world, there is an explanation of barrel aging, but there is no information specific to mead beyond what has already been explained.

However, there is Schramm's valuable experience regarding mead aging.

• Unheated mead is ready to drink in 6–8 months.

• Heated or boiled mead takes a year to become drinkable and another year to mellow out.

• Lighter meads peak at 1–2 years.

Except for barrel aging, we don't usually age our mead for that long, but it is very common for mead kept for over a year to taste amazing.
Therefore, you can enjoy the intrigue of aging by storing it in a cellar at 10–16°C away from direct sunlight.

Oxidation of Mead

We have seen that oxidative aging is a major element of barrel aging.

In this regard, mead is characterized by having fewer polyphenols than wine or beer.
Having fewer polyphenols could be said to mean it is harder to oxidize.
In fact, it is rare to feel the kind of oxidation in mead that you would find in wine.

Considering this, mead might be a type of alcohol suited for oxidative aging.

Basically, if you want to maintain a fresh aroma and taste, you prevent oxidation; if you want a sherry-like character, you intentionally use oxidative aging.

As there is still little information on barrel-aging mead, we will likely learn more as the number of people making and drinking mead increases.