Winemaking Process

Winemaking Is Decision-Making

A winemaker's job is making decisions. Hundreds of them, from harvest timing to bottling, each one steering the wine in a particular direction. Understanding these decisions — why they're made and what they do to the wine — is what separates someone who drinks wine from someone who understands it.

The raw material is grape juice. The finished product is something infinitely more complex. This chapter traces the journey and explains the choices that shape every bottle.

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Harvest — When to Pick

Harvest timing is the first and arguably most consequential decision. As grapes ripen on the vine, sugar rises, acidity falls, and flavour compounds develop. Pick too early and the wine will be tart, green, and thin. Pick too late and it will be flabby, alcoholic, and jammy. The art is finding the moment of balance.

What the winemaker measures

• Sugar level (Brix, Baumé, or Oechsle) — this determines potential alcohol
• Acidity (pH and titratable acidity) — this determines freshness and ageing potential
• Phenolic ripeness — tannin maturity in reds (unripe tannins taste green and bitter)
• Flavour development — tasting the grapes themselves

Hand vs machine harvest

Hand harvesting allows selective picking (taking only the ripest bunches), is essential on steep slopes (Mosel, Douro, Côte-Rôtie), and is gentler on fruit. It's also slow and expensive. Some appellations require it — Champagne, Beaujolais Crus.

Machine harvesting is fast, efficient, and can work at night (important in warm climates where cool temperatures preserve acidity). Modern machines are increasingly gentle, though they can't be used on steep terrain or for whole-cluster pressing.

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Crushing and Pressing

After harvest, grapes are typically destemmed (stems separated) and crushed (skins gently broken to release juice). What happens next depends on whether you're making white, red, or rosé.

• White wines: Grapes are pressed immediately after crushing. The clear juice is separated from the skins before fermentation begins. Minimal skin contact preserves the fresh, fruity character
• Red wines: Crushed grapes (juice, skins, seeds, and sometimes stems) go into the fermentation vessel together. The skins stay in contact with the juice throughout fermentation, releasing colour, tannin, and flavour
• Rosé wines: Brief skin contact (2–24 hours) gives a pink tint, then the juice is pressed off and fermented like a white wine

Pressing methods

• Pneumatic press: An inflatable bladder applies gentle, even pressure. Now the standard for quality wine
• Basket press: Traditional, very gentle. Still used in Champagne and some traditional estates
• Free-run juice (vin de goutte) flows before pressing — it's lighter, more delicate. Press wine (vin de presse) is more tannic and deeply coloured. Winemakers decide how much press wine to include in the final blend

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Fermentation — Where Sugar Becomes Wine

Alcoholic fermentation is the core transformation: yeast cells consume sugar and produce ethanol (alcohol) and carbon dioxide.

The equation is simple: Sugar + Yeast → Alcohol + CO2. The art is everything that surrounds it.

Temperature

Temperature during fermentation is one of the winemaker's most powerful levers.

Above 35°C, yeast can die, causing a stuck fermentation — a winemaker's nightmare. Modern wineries use jacketed stainless steel tanks with cooling systems for precise temperature control.

Yeast

• Cultured yeast (inoculated): commercially selected strains of Saccharomyces cerevisiae. Predictable, reliable, lower risk. The winemaker chooses a strain to emphasise certain characteristics (thiol production, temperature tolerance, alcohol tolerance)
• Indigenous yeast (wild, ambient): naturally present on grape skins and in the winery environment. More complex flavour development but higher risk of off-flavours or stuck fermentation. Includes non-Saccharomyces genera that dominate early fermentation before being outcompeted

Many top producers use indigenous yeast because they believe it better expresses the vineyard's character. It's a philosophical and practical choice.

Fermentation vessels

The container shapes the wine:

• Stainless steel tanks: Inert, easy to clean, excellent temperature control. The default for fresh, fruit-driven wines
• Oak barrels: Micro-oxygenation plus oak flavour integration during fermentation. Classic for white Burgundy — fermenting Chardonnay in barrel produces a seamlessly integrated oak character quite different from aging in barrel after fermentation
• Concrete tanks: Excellent thermal stability (thick walls), semi-porous allowing gentle oxygen exchange. Traditional in Bordeaux; modern egg-shaped concrete vessels (Nomblot) create natural lees circulation. Neutral in flavour
• Amphora / qvevri: Clay vessels buried in the ground — the 8,000-year-old Georgian tradition. Porous, allowing oxygen exchange without adding flavour. Adds textural complexity

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Maceration — Extracting Colour and Tannin

Maceration is the contact between juice and solid matter (skins, seeds, sometimes stems). It's primarily a red wine technique and determines the wine's colour depth, tannin level, and flavour intensity.

Pre-fermentation cold soak

The must is held at 5–15°C for 2–5 days before fermentation begins. This extracts colour and fruit aromatics without harsh seed tannins (which require alcohol to dissolve). Common for Pinot Noir and Grenache, where gentle extraction preserves elegance.

Extended maceration

After fermentation completes, the wine remains on the skins for additional days or weeks. This allows tannin molecules to polymerise (link together), which can paradoxically soften tannin texture over time. Used for age-worthy reds like Barolo and Bordeaux.

Carbonic maceration

Whole, uncrushed berries are sealed in a vessel flooded with CO2. Fermentation begins inside the intact berry — an intracellular process that produces very fruity, low-tannin, aromatic wines. This is the technique that defines Beaujolais Nouveau: cherry, banana, bubblegum, immediate pleasure.

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Malolactic Fermentation (MLF)

Not technically a fermentation — it's a bacterial conversion. Lactic acid bacteria (principally Oenococcus oeni) convert sharp malic acid (the acid in green apples) to softer lactic acid (the acid in milk).

What MLF does

• Softens acidity — the wine feels rounder, less tart
• Adds body and a creamy mouthfeel
• Produces diacetyl — the compound responsible for buttery aromas (especially prominent in oaked Chardonnay)
• Improves stability — removes a potential food source for spoilage bacteria

When it's used

• Almost all red wines undergo MLF as standard — reds need the softening
• Full-bodied whites where richness is desired: Chardonnay (Burgundy, California), Viognier
• Deliberately prevented in aromatic whites where fresh acidity is essential: Riesling, Sauvignon Blanc, Albariño. Prevention is achieved by chilling the wine or adding sulphur dioxide

The buttery quality of a classic Meursault (Burgundy Chardonnay)? That's MLF plus oak. The razor-sharp zing of a Sancerre (Sauvignon Blanc)? That's no MLF, no oak — pure fruit and acidity.

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Maturation — Shaping the Wine's Character

After fermentation, wine may be aged before bottling. The choice of vessel, duration, and technique is one of the winemaker's most expressive decisions.

Oak Aging

Oak barrels contribute three things: flavour compounds, tannin, and controlled micro-oxygenation (oxygen passes slowly through the wood, softening the wine).

French vs American Oak

French oak staves are split along the grain (lower yield, higher cost); American oak is sawn (more efficient). This structural difference affects porosity and flavour delivery.

New vs Used Oak

The age of a barrel dramatically changes its impact:

• New oak (first fill): Maximum flavour and tannin extraction. Intense vanilla, toast, spice. 100% new oak is a bold statement — First Growth Bordeaux, premium Napa Cabernet
• Second fill (1 year old): Softer oak influence, more about texture than flavour
• Third fill and beyond: Essentially neutral — provides micro-oxygenation without adding flavour. Useful for gentle maturation
• After 4–5 uses: Fully neutral. Some producers prefer this — all the benefits of slow oxygen exchange, none of the oak flavour

Oak Alternatives

Cheaper than barrels: oak chips, staves, and spirals can be added to stainless steel tanks to impart oak flavours. They cannot replicate the micro-oxygenation of a barrel, so the integration is less seamless. Prohibited in some traditional appellations.

Stainless Steel Aging

Inert, flavour-neutral. Preserves primary fruit character and freshness. The default for wines meant to be enjoyed young: Sauvignon Blanc, Pinot Grigio, Albariño, Vinho Verde.

Lees Aging

Lees are dead yeast cells that settle after fermentation. Leaving wine in contact with its lees (and sometimes stirring them — bâtonnage) adds richness, creaminess, and a bready or biscuity complexity. This is standard practice in Champagne (where extended lees aging is what gives the wine its toasty character) and in Muscadet (sur lie).

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Fining and Filtration — Finishing the Wine

Before bottling, most wines are clarified to remove haze-causing particles.

Fining

Fining agents are added to the wine. They bond with unwanted particles and precipitate to the bottom, where they're removed. Common agents:

• Bentonite (clay) — removes proteins in whites; vegan
• Egg white — softens harsh tannins in reds; not vegan
• Isinglass (fish bladder) — removes haze in whites; not vegan
• Pea protein — tannin softening; vegan

Filtration

Wine is passed through filters to remove remaining particles and microorganisms. Ranges from coarse (pad filtration) to sterile (0.45 μm membrane filtration). Sterile filtration ensures no refermentation in bottle.

The "natural" question

Some winemakers choose to bottle without fining or filtration, believing it preserves more body, texture, and character. The wines may be slightly hazy — not a fault, but a stylistic choice. Most wines labelled "unfined and unfiltered" are higher-end bottles where the winemaker is making a deliberate statement.

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Closures — The Final Decision

The cork-vs-screwcap debate continues, but increasingly quality producers — especially in Australia, New Zealand, and Austria — are using screwcaps for all their wines, including age-worthy bottles. There is no quality stigma.

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Putting It Together

Every wine you taste is the result of a chain of decisions. Understanding this chain lets you work backwards from the glass: Why does this wine taste this way?

A buttery, vanilla-scented Chardonnay? The winemaker chose ripe grapes, oak barrel fermentation, malolactic conversion, and lees stirring. A bright, mineral Sancerre? Early harvest, stainless steel, no MLF, bottled young. A tannic, age-worthy Barolo? Long maceration, extended aging in large oak barrels, years of patience.

The winemaker is the author, and the wine is the story. Now you can read it.