Behind Winemaking: Oak vs Stainless

Oak Barrels vs. Stainless Steel vs. Concrete Eggs

Oak Barrels

Oak barrels do two main things to a wine: add flavors and oxygenate. The flavors come from naturally occurring compounds in the oak that seep into the wine, creating vanilla, spice, and woody notes. The oxygen comes directly through the staves (the wood slats that form the sides of the barrel) and through the bung hole (the small opening in the center of the barrel). The oxygen breaks down tannins, smoothing out the wine, and leads to evaporation, gradually reducing the wine, much like a chef might reduce a sauce. 

Types of Oak

There are three main types of oak used for wine barrels: French, Hungarian, and American. 

French oak (Quercus robur) is tight-grained, meaning it allows less oxygenation and imparts a subtle and smooth texture. French oak is more tannic than Hungarian and American oak, imbuing a wine with spicier notes. Because of its heritage and quality, French oak is by far the most expensive and remains the industry standard for high-end winemaking. 

Hungarian oak is the same species as French oak therefore its overriding effect is similar, however it has slightly different qualities because it is grown in a different environment. (It turns out terroir doesn’t apply only to vines.) There is one major difference though. Hungarian oak is significantly less expensive, offering winemakers an opportunity to get that desired “French effect” at a cheaper cost.  

American oak (Quercus alba), a different species than French and Hungarian oak, is coarse-grained, which allows for more oxygenation, and is denser, meaning the flavors it imparts are bolder. The signature aromas and flavors of American oak are vanilla, coconut, and dill. It is also known to create a creamy texture and a sweeter palate. 

If you remember anything, remember the following:
– Wines aged in French oak are subtle and silky.

– Hungarian oak has a similar effect to French oak at a fraction of the cost.

– Wines aged in American oak are bold and rugged.

Barrel age

A new barrel has the strongest influence on a wine’s flavor. A barrel that has been used once (called a second pass barrel) imparts less flavor. A barrel that has been used twice (a third pass barrel) imparts even less. Following a fourth fill, a barrel is deemed neutral, so, though it still breathes, it isn’t imparting any significant flavor. Typically, winemakers use a combination of different barrel ages to achieve a specific structure and flavor balance, which is why you’ll often see a barrel age breakdown in production notes. 

Toast level

During a barrel’s construction, it is toasted over a small fire. This process caramelizes the wood’s carbohydrates, enhancing natural flavor compounds in the oak. The longer a barrel is toasted, the stronger and heavier the flavors become, and new flavors get unlocked as others fade. Similar to how coffee roasts range from light to dark, barrel toast levels range from light to heavy.

Barrel size

In a larger barrel a smaller percentage of the wine is in direct contact with the wood, therefore the wood imparts less flavor and and less oxygenation occurs. In a smaller barrel, a higher percentage of the wine is in contact with the wood, therefore the wood has a greater impact on the flavor and oxygenation increases.

Stainless steel

Insulated stainless steel tanks are great for winemakers who don’t want to impart the flavors of oak onto the wine. Wines aged in stainless steel are known for being clean, crisp, light, terroir driven, and more fruit forward. Though used across an array of varietals, insulated stainless steel tanks are particularly beneficial in the crafting of white wines, allowing winemakers to keep the wine cold, preventing oxidation. However, winemakers will often age a small percentage of a red wine in stainless steel to preserve the essence of the fruit while the rest is aged in oak barrels.

Insulated stainless steel tanks are easier to clean than barrels and effectively endlessly reusable, reproducing the same conditions each fill. These attributes make stainless steel a cheaper, more consistent option for winemakers in the long term.

Concrete

Though concrete fermentation vats have long been a fixture in cellars, concrete’s role in aging vessels began relatively recently with the creation of the concrete egg in 2001. Proponents claim concrete possesses the best of stainless steel and oak, oxygenating the wine without imparting the flavors of oak. The porous inner surface of concrete traps oxygen, which helps break down tannins for a smoother mouthfeel, and is particularly beneficial for crafting a softer, creamier style of white wine.

Concrete eggs are naturally insulating, which provides the winemaker an added element of temperature control. Like stainless steel, concrete eggs effectively last forever, as long as they are cleaned and treated properly.