Advanced Winemaking

Winemaking as Applied Chemistry

At Level 3, the winemaker's decisions are no longer a general narrative — they are a specific, consequential chain of chemical and physical interventions. Each technique solves a problem or shapes a style, and each carries trade-offs. Understanding the why behind each choice, and the science that governs it, is what separates competent description from genuine comprehension.

---

Harvest and Pre-Fermentation

Sorting and Selection

Modern quality-focused wineries employ multiple levels of selection: vineyard sorting (picking only ripe bunches), vibrating sorting tables (removing MOG — material other than grapes), and optical sorters (cameras identifying and ejecting individual damaged berries). The goal: only healthy, optimally ripe fruit enters the winery.

Crushing and Destemming

Most grapes are destemmed (stems removed) and gently crushed before fermentation. The choice to include some or all stems is a significant stylistic decision.

Whole-cluster fermentation: Retaining intact clusters (stems included) during red fermentation. The stems contribute tannin structure, lower pH slightly, and add spice and herbal complexity. They also create a "scaffolding" effect in the fermenter that promotes gentle extraction. Common in Burgundy (up to 100% whole cluster for some Pinot Noir producers), Cornas, and increasingly in Syrah production worldwide. Risk: unripe stems add green, astringent tannins.

Skin Contact for White Wines

Brief skin contact before pressing (2–24 hours) extracts additional flavour and textural compounds from white grape skins. Extended skin contact (days to months) produces orange wine — white grapes vinified like reds, with tannin structure, amber colour, and oxidative complexity. The tradition originates in Georgia (qvevri) and is now practised worldwide.

---

Fermentation Chemistry

Alcoholic Fermentation

The primary reaction is straightforward:

C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂

But this equation conceals the complexity. Yeast also produces hundreds of secondary metabolites — esters (fruity aromas), higher alcohols (fusel oils), glycerol (contributing body and viscosity), succinic acid, and many trace compounds that collectively create wine's aromatic complexity.

Yeast Selection

Cultured yeast (Saccharomyces cerevisiae): Selected commercial strains chosen for specific properties — temperature tolerance, alcohol tolerance, thiol release (enhancing Sauvignon Blanc's tropical character), or ester production. Predictable, reliable, lower risk of stuck fermentation.

Indigenous yeast (wild, ambient): Multiple species naturally present on grape skins and in the winery. Non-Saccharomyces genera (Kloeckera, Candida, Hanseniaspora) dominate the early stages, producing distinctive flavour compounds, before being outcompeted by S. cerevisiae as alcohol rises. The result can be more complex, more site-specific — or it can fail.

The choice is both practical and philosophical. Many of the world's top estates use indigenous yeast because they believe it better expresses terroir. The risk is managed through meticulous vineyard hygiene and cellar experience.

Temperature Control

Modern wineries use jacketed stainless steel tanks with integrated cooling/heating systems for precise control. Some producers deliberately allow fermentation temperatures to rise briefly (peak extraction), then cool rapidly.

Fermentation Vessels

The vessel is not neutral — it participates:

• Stainless steel: Inert. No flavour contribution. Excellent temperature control. The default for fruit-driven, clean wines
• Oak barrels: Flavour compounds (vanillin, lactones, eugenol) integrate during fermentation, producing a more seamless oak character than post-fermentation aging alone. Barrel fermentation also allows micro-oxygenation from the start. Standard for white Burgundy, premium Napa Chardonnay
• Concrete: Semi-porous, allowing gentle oxygen exchange. Excellent thermal mass. Modern egg-shaped vessels (Nomblot) create natural convection currents that keep lees in suspension. Neutral in flavour
• Amphora / qvevri: The Georgian tradition (8,000 years old). Clay is porous, allowing oxygen exchange without flavour contribution. Buried in the ground for temperature stability. Adds textural complexity

---

Maceration and Extraction

Extraction Dynamics

Extraction from grape skins is not linear. Different compounds extract at different rates and under different conditions:

• Colour (anthocyanins): Extracts rapidly, even without alcohol. Maximum colour is reached within a few days
• Tannin (proanthocyanidins): Extracts more slowly and requires alcohol as a solvent. Seed tannins extract later and are harsher than skin tannins
• Flavour compounds: Extract throughout maceration, with complexity increasing over time

Extraction Techniques

Cold Soak (Pre-Fermentation)

Must held at 5–15°C for 2–5 days before yeast activity begins. Extracts colour and fruit aromatics without alcohol (which dissolves harsher tannins). Favoured for Pinot Noir and Grenache where elegance, not power, is the goal.

Extended Maceration (Post-Fermentation)

Wine remains on skins after fermentation completes, sometimes for weeks. During this period, tannin polymers link together (polymerisation), which paradoxically softens the tannin texture. Used for age-worthy reds — Barolo, Bordeaux, Napa Cabernet.

Carbonic Maceration

Whole, uncrushed berries sealed in CO₂. Intracellular fermentation occurs within intact cells, producing about 2% ABV before the berries are crushed and conventional fermentation begins. The result: intensely fruity, low-tannin wines with distinctive banana, bubblegum, and cherry aromas. Definitive for Beaujolais Nouveau. Semi-carbonic maceration (only the bottom berries are crushed by the weight of those above) is more common in practice.

---

Malolactic Conversion

Lactic acid bacteria (Oenococcus oeni) convert malic acid to lactic acid:

Malic acid → Lactic acid + CO₂

The effects: reduced perceived acidity (lactic is softer than malic), increased body and mouthfeel, production of diacetyl (the buttery compound), and improved microbiological stability.

Standard for virtually all red wines. For whites, it's a stylistic choice:

• Encouraged: Chardonnay (Burgundy, California — adds richness and complexity), Viognier
• Prevented: Riesling, Sauvignon Blanc, Albariño — where primary fruit and fresh acidity are essential. Prevention via low temperature, SO₂ addition, or sterile filtration

Partial MLF (allowing conversion in only a portion of the wine) offers a middle path — some softening without losing all the malic freshness.

---

Sulphur Dioxide (SO₂) Management

SO₂ is the winemaker's most important chemical tool — serving simultaneously as:

• Antioxidant: Prevents browning and preserves fresh character
• Antimicrobial: Inhibits spoilage bacteria and wild yeast
• Anti-enzymatic: Blocks oxidative enzymes (polyphenol oxidase, laccase)

Free vs Bound SO₂

Total SO₂ in wine exists in two forms: free (the active, protective fraction) and bound (combined with other molecules, no longer protective). The winemaker monitors and maintains free SO₂ at sufficient levels — typically 20–40 mg/L for whites, 20–30 mg/L for reds.

SO₂ and pH

Free SO₂ is more effective at lower pH. At pH 3.0, approximately 6% of free SO₂ is in the active molecular form; at pH 3.5, only about 3%. This means higher-pH wines (from warm climates) require more total SO₂ to achieve the same protection — one reason why acidity management matters.

The "Natural Wine" Debate

Natural wine producers minimise or eliminate SO₂ additions, relying on careful vineyard practice, indigenous yeast, and gentle handling to protect the wine. The trade-off: greater risk of oxidation, microbial instability, and premature ageing, but potentially a more vivid, immediate, site-specific expression. There is no legal definition of "natural wine" — it is a philosophy, not a classification.

---

Maturation Regimes

Oak: The Science of Flavour

Oak contributes through three mechanisms: flavour compounds released from the wood, tannin (ellagitannin — structurally different from grape tannin), and controlled micro-oxygenation through the semi-porous staves.

Compound Contributions

Toast Levels

Barrels are toasted (heated) during coopers' finishing — the degree of char dramatically affects flavour:

• Light toast: More raw wood character; coconut, vanilla
• Medium toast: Balanced; spice, vanilla, light smoke
• Heavy toast: Smoke, espresso, dark chocolate; can mask fruit if overdone

Size Matters

Standard Bordeaux barrique: 225 litres. Larger vessels (500L demi-muid, 2,000+ litre foudre) have a lower surface-area-to-volume ratio, meaning less oak flavour extraction and slower oxygenation. Many producers of Nebbiolo, Sangiovese, and Pinot Noir prefer larger, older oak — the goal is gentle maturation, not flavour overlay.

Lees Aging and Bâtonnage

Lees (dead yeast cells) release mannoproteins and amino acids during autolysis, adding creaminess, body, and biscuity complexity. Bâtonnage (stirring the lees) accelerates this process and keeps lees in suspension. Standard practice for Muscadet sur lie, white Burgundy, and Champagne (where extended lees aging is the defining technique).

Micro-Oxygenation

Controlled introduction of tiny amounts of oxygen into wine in tank (via ceramic diffusers), simulating the slow oxygenation of barrel aging. Softens tannins and accelerates polymerisation. Used for commercial reds where barrel cost is prohibitive — can improve quality at scale, but cannot replicate the full complexity of barrel maturation.

---

Finishing: Fining, Filtration, and Bottling

Fining

Fining agents bond with target molecules and precipitate them. The choice of agent depends on the problem:

Filtration

• Pad / sheet filtration: Wine passes through cellulose pads. Removes particles down to a specified size
• Membrane filtration (0.45 μm): Sterile filtration. Removes all microorganisms, preventing refermentation in bottle. Standard for wines with residual sugar
• Cross-flow filtration: Continuous process; wine flows across the membrane surface rather than through it. More efficient, less wasteful

Unfiltered and Unfined

Some winemakers deliberately avoid fining and filtration, believing it strips body, texture, and character. The wines may show slight haze — not a fault, but a statement. This is more common in premium, small-production wines where the winemaker can accept the risk.

Bottling

Modern bottling lines purge bottles with inert gas (N₂ or CO₂) to minimise oxygen pickup. SO₂ is adjusted to target free levels. Sterile bottling passes wine through a 0.45 μm membrane immediately before filling.

Closures

The closure choice affects how a wine evolves over years — the rate of oxygen ingress determines whether the wine develops oxidative complexity (slow cork maturation) or retains reductive freshness (screwcap preservation).

---

Sparkling and Fortified: Advanced Techniques

Traditional Method — The Detail

The complexity of traditional-method sparkling wines comes from autolysis — the breakdown of dead yeast cells during lees aging. The enzymes released cleave mannoproteins, producing the biscuity, brioche, toasty character that distinguishes Champagne from tank-method sparkling wine. Minimum lees aging: 15 months (Champagne NV), 36 months (vintage), up to 60 months (Franciacorta Riserva). Many prestige cuvées age 5–10 years on lees.

Dosage — the addition of liqueur d'expédition after disgorgement — is the final stylistic calibration. Brut Nature (0–3 g/L sugar) to Doux (> 50 g/L). The trend over the past two decades is toward lower dosage (extra brut, zero dosage), allowing the wine's natural character to speak.

Fortified Wine — The Chemistry

Port: Fortification with 77% ABV aguardente at 6–9% ABV arrests fermentation, leaving 70–100 g/L residual sugar. The ratio of spirit to wine is approximately 1:4. Ruby-style ports undergo reductive aging (tank/bottle); tawny-style ports undergo oxidative aging (small barrels, extended).

Sherry: Biological aging under flor (Saccharomyces yeast film) requires specific conditions: 15–15.5% ABV, humidity, and 15–20°C. The flor consumes glycerol and produces acetaldehyde — responsible for Fino's distinctive tangy, almond character. The solera system provides fractional blending across vintages: wine is drawn from the bottom tier (solera) and replenished from criaderas above, ensuring consistency without a vintage date.