Oak in winemaking

In general terms - how does oak improve the quality of wine and spirits?

• improves flavour, colour & stability

• reduces astringency

• enhances character and complexity

  • slow evaporation, controlled oxidation, flavour extraction

When do oak trees reach maturity?

suitable for harvesting after 80 years

What type of oak is typically used for barrel manufacture?

White oak

european - Quercus penduculata and sessilis

american - Quercus alba

What part of the oak tree is used to make barrels?

Only the heartwood

What does the extraction of volatiles into wine and spirits depend on?

• duration of maturation

• size of barrel - extractable surface area

• previous use of barrel - new or old

• type and origin of oak - French/european vs American

• toasting level - The degree of barrel toasting (light, medium, heavy) alters the breakdown of oak lignin, hemicellulose, and cellulose, influencing the release of vanillin, lactones, and spice-like phenolics. Higher toasting levels generally increase the presence of smoky and caramelized notes

• oxygen exposure - Micro-oxygenation through the barrel staves and controlled oxygenation in winemaking impact the oxidative reactions that modify oak volatiles and enhance aroma complexity

• wine composition - The alcohol content and pH of the wine affect extraction rates. Higher alcohol enhances the solubility of aromatic compounds, while lower pH can influence the breakdown of tannin

• temperature and humidity - Warmer cellaring conditions accelerate volatile extraction, while cooler conditions slow the process. Humidity affects evaporation rates and barrel permeability

List the two structural properties that give oak wood the strength, durability and workability required for barrel cooperage

1. Tyloses Formation

2. Grain Structure and Medullary Rays

Explain Grain Structure and Medullary Rays in terms of oak wood strength, durability and workability

Oak has a dense and tight grain structure with prominent medullary rays. These rays provide structural integrity and resistance to splitting, ensuring the wood remains strong under the stress of barrel construction and usage. The grain structure also allows coopers to bend and shape the wood into curved staves while maintaining its strength, making oak highly workable for barrel production

Explain Tyloses Formation in terms of oak wood strength, durability and workability

Oak wood contains tyloses, which are outgrowths that form in the xylem vessels. These tyloses block the vessel elements, making the wood watertight and preventing excessive evaporation or leakage of wine during maturation

Why are oak toasting levels important when choosing a barrel to age wine in?

Oak toasting levels are crucial in barrel selection as they influence flavor, aroma, tannin extraction, and wine structure:

• Light Toast – Preserves fresh oak and coconut notes, with higher tannin extraction for structure.

• Medium Toast – Balances vanilla, spice, and oak integration, suitable for many wine styles.

• Heavy Toast – Enhances smoky, caramel, and roasted notes while softening tannins.

Lighter toasts suit delicate wines (e.g., Chardonnay, Pinot Noir), Medium toasts work well for balanced integration in red wines like Merlot and Tempranillo, while heavier toasts complement bold reds (e.g., Cabernet Sauvignon, Shiraz). The right toasting level ensures harmony between oak influence and wine style

What does thermal degradation do to polysaccharides in toasting?

Polysaccharides give maltol (caramel toffee), cyclotene (maple, burnt sugar), furans (toasted, nutty)

What does thermal degradation do to lignin in toasting?

Lignins give vanillin (vanilla, sweet), guaiacol (smoky, charred), eugenol (spicy, clove) and phenolics