From barrel fermentation to the angel’s share, discover how oak shapes wine’s flavour, texture and ageing potential through the insights of Koos Grenache and Professor Octavius Pinot.

The cellar is cool and dim, the air carrying the quiet scent of wood, spice and something slowly evolving. Rows of barrels stretch into shadow.

Koos Grenache uses a pipette (wine thief) to pour wine into Octavius’s glass

Koos

“Ah, oak. The winemaker’s favourite hiding place. Get heavy-handed with it and suddenly everything tastes expensive.”

Octavius Pinot
“Or, when used with restraint, it becomes invisible — which is precisely the point.”

Koos
“If I can taste the tree before the grape, we’ve got a problem.”

What oak actually does

Octavius
“Wine does not simply sit in oak — it interacts with it.”

Over time, three things happen:

• Tiny amounts of oxygen pass through the wood
• Tannins soften and knit together
• Compounds from the oak dissolve into the wine

Koos
“So it’s not just flavour. It’s teaching the wine some manners.”

Octavius
“Structure, texture, and longevity. Oak shapes how a wine feels as much as how it tastes.”

Oak has terroir too

Octavius
“The origin of the oak matters just as much as the origin of the grapes.”

• Tronçais Forest – fine-grained, slow, elegant
• Nevers – firmer spice
• Vosges – aromatic lift
• Slavonia – often used for large casks

Koos
“So now we’re drinking forests as well as vineyards.”

French oak vs American oak

Koos lifts two glasses side by side.

Koos
“This one smells like spice and polish. That one smells like someone baked a vanilla cake.”

Octavius
“You’ve just discovered the difference between French and American oak.”

French oak

Often sourced from forests like Tronçais and Nevers.

• Tight grain
• Slower flavour release
• Notes of spice, cedar, and structure

Koos
“So it whispers.”

American oak

• Wider grain
• Faster, more obvious extraction
• Notes of vanilla, coconut, and sweet spice

Koos
“No whispering there.”

South African preference

Octavius
“Most premium South African producers favour French oak.”

• Better integration with fruit
• More restraint
• Greater ageing potential

Koos
“We’ve got enough sunshine in the vineyard. We don’t need the barrel shouting over it.”

A famous exception

Octavius
“Wines like Penfolds Grange show how well American oak can work in the right hands.”

Koos:
“Which proves — it’s not the tool, it’s how you use it.”

Why not South African oak

Octavius
“A common question. Local oak tends to grow faster, producing wider grain and less predictable extraction.”

Koos
“Fine for furniture. Not ideal for fine wine.”

Before the barrel exists

Oak logs are split, not sawn, then stacked outdoors for 18 to 36 months.

Rain and sun leach out harsh tannins. The wood slowly settles before it is shaped.

Fire and flavour

Inside the cooperage, the barrel is toasted over an open flame.

• Light toast gives structure and subtle spice
• Medium toast gives balance
• Heavy toast gives smoke, coffee and darker notes

Octavius
“This is where flavour is shaped.”

Koos
“And occasionally overdone.”

Barrel sizes

Octavius
“Size determines influence. There is also a more technical way to understand why size matters — surface area.”

A 300 litre barrel has a surface area of roughly 2.4 square metres, which equates to about 80 square centimetres of wood contact per litre of wine.

A 500 litre barrel, with a surface area of around 3 square metres, provides closer to 60 square centimetres per litre.

Koos
“So the bigger the barrel, the less wood each litre of wine has to deal with.”

Octavius
“Exactly. Less surface contact means a more subtle oak influence and a slower, gentler evolution.”

• 225 litre barrique – pronounced oak impact
• 300 litre hogshead – more balanced expression
• 500 litre puncheon – subtle oak, more fruit
• Foudre (1,000 litres and above) – minimal flavour, gentle ageing

Cost, care and the angel’s share

Octavius:
“Barrel fermentation and maturation is not cheap.”

• A new barrel can cost between R15,000 and R30,000 or more
• It contributes meaningful flavour for only a few years (1 – 4 years)
• It requires space, time and constant care

As wine ages, a small portion evaporates through the wood — the angel’s share.

Barrels must therefore be topped up regularly to prevent oxygen from spoiling the wine.

Koos:
“So the angels get their cut, and the winemaker keeps refilling the glass.”

New, second fill and third fill

Octavius:
“A barrel’s influence softens with use.”

• New oak gives strong flavour
• Second fill is more integrated
• Third and fourth fill becomes largely neutral

Barrel fermentation and Chardonnay

In a quiet corner, barrels gently bubble during fermentation.

Octavius
“When wine ferments in barrel, the oak becomes part of its foundation, not something added later. Not every white wine benefits from oak fermentation or maturation in oak — it all comes down to the style the winemaker is trying to create.”

After fermentation, the wine rests on its lees — spent yeast cells.

Winemakers stir these lees, a process known as bâtonnage.

Over time, the wine develops:

• Creaminess
• Bread-like richness
• Greater texture and depth

Why fermentation for red wines is different

Octavius
“Red wines ferment with skins, forming a cap that must be managed.”

Koos
“Try doing that inside a small barrel and you’ll need a very small winemaker.”

A lesson from Vega Sicilia Único

Octavius
“One of the world’s great wines. It spends many years ageing before release.”

Koos
“And not drowning in new oak?”

Octavius
“Mostly older barrels.”

Koos
“Which proves the point. Great wine is about balance, not volume.”

Alternatives and shortcuts

Octavius:
“Some producers use oak chips or staves. While they add flavour, they cannot replicate the slow oxygen exchange of a barrel.”

Koos:
Ah, the express lane to ‘oak character’.”

Closing Note

Oak is not simply a flavouring. It is a slow, deliberate conversation between wood, air, time and wine.

Handled well, it becomes almost invisible — yet its effect is everywhere.

Koos finishes his glass and sets it down.

Koos
“A good barrel doesn’t shout. It just quietly makes the wine better.”