Vinification

Vinification — The Cellar

Description

The complete technical journey of grape to bottle: harvest decisions, fermentation science, maceration techniques for red wines, the mechanics and effects of malolactic conversion, oak treatment options and their flavor impacts, pressing and fractional blending, fining and filtration choices, and the sulfur dioxide debate. Covers both conventional and natural wine approaches to each stage, explaining the tradeoffs that define every winemaker's decisions.

Skill Type

Knowledge

Harvest Decisions

The decisions made in the first hours after grapes arrive at the winery fundamentally determine the wine's potential. They cannot be undone.

Machine vs Hand Harvest

Machine harvest: A mechanical harvester straddles the vine row and beats the canopy with rubber rods, dislodging berries into collection bins. Fast, available 24/7, cost-efficient at scale.

• Advantages: Speed (can harvest the entire vintage in days), available at night (temperature control), no labor shortage vulnerability, feasible on flat terrain at any hour
• Disadvantages: Cannot select individual clusters; picks everything regardless of health or ripeness; some skin breakage and juice oxidation during collection; impossible on very steep slopes (Côte-Rôtie, Mosel, Priorat, Douro); cannot be used for whole-cluster processing (clusters are broken apart)
• Use cases: Large estates in Languedoc, generic Bordeaux, Rioja (commercial tier), New World commodity wine

Hand harvest: Human pickers make individual cluster selections with shears or knives.

• Advantages: Selective picking (leave unripe or damaged clusters; take only what's ready); essential for whole-cluster processing; required for dessert wines (botrytized grapes must be selected berry by berry at estates like Château d'Yquem — multiple passes through the vineyard); required on steep slopes; gentler handling
• Disadvantages: Expensive (labor cost 5–10x machine harvest); requires reliable skilled labor; slower (timing critical in unstable weather); can only work daylight hours in most arrangements (though night harvesting with lights is practiced)

Night Harvest: Increasingly common in warm climates (Napa, Barossa, Rhône during heat waves). Grapes harvested at 2–4°C ambient temperature arrive at the winery cold, reducing oxidation and allowing greater aromatic preservation. Temperature control at harvest is a significant quality factor in warm-climate winemaking.

Whole Cluster vs Destemmed

Destemming: The standard approach. A destemmer-crusher removes stems from clusters before fermentation. Most red and all rosé wine. Benefits: Removes stems (which add astringency and, if unripe, green/herbal character); allows more extraction control; standard baseline.

Whole cluster: Keeping some or all stems intact, fermenting uncrushed or partially crushed.

• Effect on wine: Adds spice, forest floor/woodland character, structural tannin (different from skin tannin — more granular, finer), cools the fermentation naturally (stems absorb heat), can reduce overall extraction
• Requirement: Stems must be phenologically ripe — brown, woody. Green stems add harsh, unpleasant green tannin.
• Producers who use high whole-cluster percentages: DRC (often 100%), Rousseau, Dujac, Ponsot (Burgundy); Sean Thackrey, Littorai (California)
• The debate: High whole-cluster extends the aromatic complexity and structural length of many Pinot Noirs but can add astringency if the stems aren't fully ripe.

Sorting Table

After harvest, grapes pass over a sorting table (or through an optical sorter in large modern facilities) where workers or machines remove:

• Damaged/rotten berries
• Underripe clusters or berries
• Leaves and vineyard debris (Mégrands)

Optical sorting: High-speed camera and air-jet system photographs each berry at up to 7 frames per second, identifies defects by color/size/shape, and removes them with targeted air jets. Expensive. Precise. Used at top estates (Pétrus, Sassicaia). Hand sorting: Two passes — one before and one after the destemmer. Labor-intensive but effective when done by skilled, attentive workers.

Fermentation

Alcoholic Fermentation: The Chemistry

Yeast converts glucose and fructose (grape sugars) into ethanol and carbon dioxide: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

One degree Brix (approximately 17 g/L of sugar) converts to approximately 0.57–0.64% ABV, depending on the yeast strain and fermentation conditions.

Temperature: The most controllable variable in fermentation.

• White wine (12–18°C): Low temperature slows fermentation, preserving volatile aromatic compounds (esters, terpenes) that would evaporate in a warm ferment. The tradeoff: slow fermentations can stick. Long, cold fermentation for Riesling and Sauvignon Blanc is standard for preserving the floral and citrus aromatic profile.
• Red wine (25–32°C): Warmer fermentation extracts color (anthocyanins are more soluble at higher temperatures), tannin, and flavor compounds from skins. Very high temperatures (above 35°C) risk killing yeast (stuck fermentation) and destroying aromatics.
• Rosé (12–15°C): Treated like white wine to preserve freshness.

Wild / Native Yeast

The grape berry, vineyard soil, and winery equipment host a complex ecosystem of yeast species — primarily non-Saccharomyces (Metschnikowia, Hanseniaspora, Starmerella, Lachancea, others) early in fermentation, which are typically succeeded by Saccharomyces cerevisiae (more alcohol-tolerant) as ethanol levels rise.

Arguments for wild yeast:

• More complex fermentation creates more diverse secondary metabolites → more complex wine
• Reflects the specific microbial ecosystem of the vineyard and winery → site expression in the fermentation
• No external inoculation → nothing added to the wine
• Beloved by natural wine movement as philosophically consistent

Arguments against:

• Higher risk of stuck fermentation (non-Saccharomyces strains are less reliable at completing fermentation)
• Higher risk of spoilage organisms (Brettanomyces, which produces the barnyard/medicinal notes, is a winery yeast that can dominate a wild ferment in unhygienic conditions)
• Variable results year to year — a warm vintage may have a completely different spontaneous flora than a cold one
• Not actually "wild" in most wineries — the dominant spontaneous flora is heavily influenced by the winery's own resident yeasts, built up over years

The practical middle ground: Many estates that ferment with "wild" or "native" yeast have built up a reliable house yeast population through decades of practice. The Burgundy négociant who hasn't inoculated since 1970 is effectively fermenting with a selected strain — just one selected by years of environmental pressure rather than a laboratory.

Cultured / Commercial Yeast

Saccharomyces cerevisiae strains selected for specific properties and freeze-dried for commercial sale.

Common strains and their characters:

• EC-1118 (Champagne yeast): Highly alcohol-tolerant, reliable, clean. Standard for sparkling wine secondary fermentation. Sometimes used as "rescue" yeast when fermentations stick.
• 71B: Enhances fruity esters, partially metabolizes malic acid, widely used for fruity styles (Beaujolais nouveau, rosé, aromatic whites)
• D80/D254: Designed for extraction of tannin and color — used in full-bodied reds
• K1V-1116: Cold-tolerant, enhances fruit aromatics, used for aromatic whites

Arguments for cultured yeast:

• Reliable, predictable fermentation completion
• Specific flavor contributions can be dialed in
• Lower risk of stuck fermentation
• Can be matched to wine style (fruity vs. neutral vs. spicy yeast)
• Standard in commercial winemaking globally

The natural wine objection: Commercial yeast strains were mostly selected for reliability and aromatic impact in laboratory conditions, not for site expression. Using the same yeast strain in Burgundy and New Zealand produces some level of homogenization that suppresses the individual character of each site.

Maceration (Reds)

Maceration is the contact between grape skins (and seeds, sometimes stems) and the fermenting juice. Everything extracted from the solid material — color, tannin, flavor — happens during maceration. Managing maceration is the central technical skill in red winemaking.

What is Being Extracted

Anthocyanins (color): Concentrated in the skin (except teinturier varieties like Saperavi, which also have them in the flesh). More soluble at higher temperatures and higher alcohol. Extracted relatively early in maceration — the first few days extract most available color.

Proanthocyanidins / Tannins: Located primarily in skins and seeds (seed tannin is different from skin tannin — coarser, harsher, higher astringency). Tannin extraction continues throughout maceration and increases with temperature, mechanical action, and alcohol level.

Flavor compounds: Extracted throughout fermentation and maceration. Varietal character compounds (pyrazines, terpenes, esters) are released from the skins and cells.

The Cap

During red wine fermentation, CO₂ gas lifts the grape skins to the surface of the tank, forming a "cap" (chapeau in French). The cap, left unmanaged, prevents the fermenting juice from contacting the skins, reducing extraction and creating hot spots where unwanted bacteria can multiply. Cap management is the daily manual labor of red winemaking.

Punch-Down (Pigeage)

Workers (or a mechanical device) submerge the cap into the juice from above using a tool resembling a large plunger. The cap is pushed down into the liquid several times per day.

• Effect: Gentle extraction. Breaks up the cap, enables skin-juice contact, keeps the cap moist and temperature-regulated.
• Standard for: Pinot Noir (where gentleness is paramount), Burgundy universally, most small to medium wineries
• Manual pigeage: A cultural tradition in Burgundy and throughout small artisan estates. Some winemakers report that human foot treading (the original method, still used in some Douro Port production) is gentler than mechanical punch-down.

Pump-Over (Remontage)

A pump draws juice from the bottom of the tank and sprays it over the top of the floating cap. Circular process: juice extracted from below, distributed over above.

• Effect: More extraction than punch-down. Also aerates the must (oxygen encourages yeast health, can help complete stuck fermentations). Good for color stability.
• Standard for: Cabernet Sauvignon, large commercial estates, any variety where more structure is desired
• Closed loop option: Pump-over without oxygen (submerged injection) avoids oxidation.

Délestage (Rack and Return)

The entire liquid portion of the tank is drained off into a separate tank. The cap, now unsupported, falls to the bottom and is briefly aerated. The drained juice is pumped back over the reassembled cap.

• Effect: Very gentle extraction, significant aeration of cap, breaks up grape seeds (which can release harsh seed tannin if repeatedly crushed). Typically done once or twice during fermentation.
• Standard for: Producers seeking gentle extraction with aromatic preservation. Common in Rhône, some Burgundy.

Cold Soak (Pre-Fermentation Maceration)

The crushed grapes are held at low temperatures (5–10°C) before fermentation begins, allowing color and fruit extraction before alcohol is present (alcohol dramatically accelerates tannin extraction).

• Duration: 3–7 days typically
• Effect: More color and fruit extraction without the tannin that alcohol-driven extraction brings. The "soft" pre-fermentation phenolics.
• Proponents: Many Burgundy and Oregon Pinot Noir producers. Jacques Lardière at Jadot was an early practitioner.
• Controversy: Does cold soak actually add complexity, or just risk (unwanted bacterial development before yeast dominates)? The evidence is genuinely mixed.

Extended Maceration (Post-Fermentation Maceration)

After fermentation is complete (all sugar converted), the wine can remain on its skins for extended periods — weeks to months.

• Effect: Continued tannin extraction AND polymerization (tannin molecules bond together into chains, becoming less astringent). The paradox: extended maceration extracts more tannin but the tannin extracted is more polymerized and thus smoother.
• Traditional Barolo: Extended maceration for 60–90 days (traditional style). The result: wine initially very tannic but with capacity for extraordinary aging and eventual silkiness.
• Modern Barolo: 7–15 days maceration. Less initial tannin, earlier drinking.
• Current: Many Barolo producers use 30–45 days — the contemporary middle ground.

Malolactic Conversion (MLF)

The Chemistry

Malic acid (found naturally in grapes and green apples — sharp, crunchy) is converted by lactic acid bacteria (primarily Oenococcus oeni) to lactic acid (found in dairy — softer, rounder) and CO₂:

Malic acid (diprotic, sharp) → Lactic acid (monoprotic, softer) + CO₂

The effect: both chemical softening (lactic acid is perceived as less harsh than malic) and pH increase (typically 0.1–0.3 pH units rise, reducing acidity).

Red Wine

All serious red wines undergo MLF. In most cases it happens spontaneously — the lactic acid bacteria are naturally present in the winery environment and begin working after alcoholic fermentation completes or sometimes simultaneously. Winemakers rarely inhibit MLF in reds because:

• High tannin red wines benefit from the acid softening
• MLF improves microbial stability (residual malic acid is a food source for bacteria; completing MLF removes this risk)

White Wine — To MLF or Not

This is one of winemaking's most consequential stylistic decisions for white wines:

Full MLF (complete malolactic conversion):

• Result: softer, rounder, creamier wine. Diacetyl (the principal secondary compound of MLF) smells of butter at high concentrations; at low concentrations, adds complexity.
• Associated with: Most serious Burgundy Chardonnay, Meursault, Puligny-Montrachet, most Napa Chardonnay, Australian Chardonnay in Burgundian style
• Mechanism: Bâtonnage (lees stirring) after MLF integrates the diacetyl into the wine's texture, reducing the butter aroma while retaining creaminess

Blocked MLF (inhibited malolactic conversion):

• Result: Crisper, fresher, more aromatic, higher perceived acidity, more apple/citrus character, reduced complexity but more primary freshness
• Methods of blocking: SO₂ (kills lactic acid bacteria), low temperature (bacteria inactive below ~15°C), lysozyme enzyme (specifically targets lactic acid bacteria), centrifugation (physically removes bacteria)
• Associated with: Riesling (acid preservation essential), Sauvignon Blanc (aromatic freshness is the point), Muscadet, most Vinho Verde, unoaked Chardonnay designed for freshness, most aromatic varieties
• Why: The high natural acid of Riesling would become flabby if fully put through MLF. Sauvignon Blanc's aromatic character would be muffled.

Partial MLF: Some wines deliberately undergo partial MLF — the conversion is allowed to proceed partway and then halted. Allows a middle ground: some added complexity and textural softening from partial conversion, while retaining more freshness and acid than full MLF.

Oak Treatment

Oak is the single most discussed winemaking input after the grapes themselves. It is also the most misunderstood — the effect of oak depends enormously on the type of oak, the format, the toast level, the ratio of new to used, and the time of contact.

French Oak vs American Oak

French Oak (Quercus robur, Quercus petraea — primarily Q. sessilis/petraea for wine):

• Tight grain (narrower rings indicate slow growth in cooler French forests)
• Finer-grained vessels mean slower extraction of tannin and aromatic compounds
• Flavor: Vanilla (subtle), cedar, spice, toast, hazelnut. Elegant, integrated.
• The French forest premium: Tronçais (finest grain, most subtle), Allier, Nevers, Vosges, Limousin (coarser grain, stronger vanilla — used for Cognac, not typically wine)
• Primary use: All Burgundy, most Bordeaux, Rhône, most fine wine globally
• Cost: €900–1,200+ per barrel (new)

American Oak (Quercus alba):

• Wide grain (faster growth in American forests)
• More aggressive extraction — more tannin and flavor compounds per unit time
• Flavor: Strong vanilla (vanillin), coconut, dill, clove, sometimes tobacco. Unmistakable.
• Historical use: Traditional Rioja (Tempranillo with American oak vanilla = classic style), old-school Barossa Shiraz (Penfolds Grange was historically American oak — recently transitioning to mixed), some Napa producers
• The "international style" move away from American oak: Post-1990s, American oak became associated with less sophisticated winemaking (too obvious, too much vanilla). Most prestige producers have shifted to French.
• Cost: €400–600 per barrel (new — significantly cheaper than French)

Hungarian / Slavonian Oak: Between French and American in grain size and flavor intensity. Slavonian oak (from Croatia/Slovenia) is traditional for large Barolo botti and has been used in Italy for centuries. Neutral when used in very large format (2,000–10,000L botti) — minimal oak flavor contribution; only structural oxygenation effect.

New vs Neutral Oak

• New oak (first fill): Maximum flavor extraction. Vanilla, toast, cedar, spice. Adds both aromatic complexity and structural tannin from the wood. After one use, loses approximately 40–50% of its extractable compounds.
• Second fill: Less extraction — still contributes but subtly
• Third fill and beyond ("neutral"): Effectively no flavor contribution. Functions purely as a vessel — allows micro-oxygenation without adding flavors.
• Why neutral oak? Many great wines age in old oak specifically because they want the slow, controlled micro-oxygenation (which helps polymerize tannins and develop complexity) without any added wood flavors.

The new oak percentage decision: Producers express their oak program as a percentage of new oak. 100% new oak (some Napa Cabernet) = maximum wood impact. 0% new oak (all neutral, as in traditional Barolo botti) = no wood flavor. Most Burgundy premiers crus: 30–50% new oak. Grand crus: 50–100% new oak. The percentage is a direct statement of the winemaker's style philosophy.

Toast Level

Barrels are fired (toasted) over flame during the coopering process. The heat chars the interior surface, creating caramelized compounds (furfural and other furanic compounds) with aromatic signatures:

• Light toast: Aromatic compounds preserved. More vanilla, more spice, more "raw" oak character.
• Medium toast (most common): Balance of aromatic contribution and structure. Cedar, vanilla, toast, some spice.
• Heavy toast / charred: Heavy smoke, coffee, dark chocolate, toasted bread notes. The char also reduces harsh tannin extraction (the carbonized surface acts as a buffer).
• Choice: Generally matches wine style. A delicate Pinot Noir might use light-medium toast to avoid overwhelming. A powerful Napa Cab might use medium-plus or heavy toast for added complexity.

Barrel Size

• Barrique (225L, Bordeaux standard) or Burgundy pièce (228L): Small size means higher ratio of oak surface area to wine volume. More oak flavor per unit time. Used for most serious Bordeaux, Burgundy, Napa, etc.
• Hogshead (300L): Less oak surface per liter. More common in Australia, some Bordeaux.
• Foudre (500–2,000L+): Very low surface area to volume. Less oak influence, more oxygenation benefit. Common in Alsace, Rhône (large format), some German producers.
• Botti (2,000–20,000L): Traditional Barolo and Barbaresco. Effectively neutral (no oak flavor) — purely a vessel for slow oxidative aging. The "traditional" Barolo style is defined by botti aging.

Oak Alternatives

• Oak chips: Small pieces of toasted oak added directly to wine in tanks or barrels. Very rapid extraction. Legal in most countries for table wine.
• Oak staves/dominoes: Larger format than chips, inserted into tanks. Slower extraction than chips.
• Oak powder: Maximum surface area, maximum speed. Commercial wine production only.
• Assessment: All oak alternatives can add flavor compounds but lack the structural oxygenation benefit of actual barrel aging. The micro-porous barrel wall allows controlled oxygen ingress (1–3 mg/L per year) that integrates compounds and softens tannin. Oak chips in a sealed tank add flavor without this critical structural benefit.

Pressing

After fermentation (reds) or immediately after crushing (whites), the grape solids must be separated from the liquid.

Free-Run Juice (Vin de Goutte)

The juice that flows from grapes purely by gravity — no applied pressure. For reds: the wine drained from the tank when the valve is opened after fermentation. For whites: the juice that flows from crushed grapes before pressing.

• Character: Finest, most elegant, lowest tannin (reds), cleanest (whites). Highest quality fraction.

Press Fractions

As increasing pressure is applied to the remaining grape solids (press wines, vin de presse), the extracted liquid becomes progressively:

• More tannic (skin and seed tannin)
• More phenolic
• More concentrated (can add color and extract)
• Less elegant
• In whites: more bitter, more phenolic, less aromatic

The blending decision: Winemakers taste each press fraction and decide how much (if any) to blend back into the free-run wine. First press fraction: often added to add structure. Subsequent press fractions: increasingly selected against for quality wines. Generic wines: more press wine included for volume and color.

Fining and Filtration

Fining

The addition of a positively-charged protein substance that bonds with negatively-charged tannin and protein molecules, forming large aggregates that fall out of the wine through sedimentation.

Common fining agents:

• Egg whites (albumin): Traditional. Add 2–6 egg whites per barrel, stir, allow to settle over 1–2 weeks. Gentle, selective for harsh tannins. Standard in fine Bordeaux and Burgundy for centuries. Not suitable for vegans.
• Bentonite clay: Negatively-charged clay that bonds with positively-charged proteins (especially heat-unstable proteins in whites that would cause cloudiness). Standard for white wine protein stability.
• Casein: Milk protein. Removes browning and oxidative phenolics. Also not vegan.
• Isinglass: Derived from fish swim bladders. Very gentle, used for white wines and beer. Not vegan.
• Gelatin: Animal-derived, similar to egg white in effect.
• Vegan options: Bentonite (standard for whites), pea protein, potato protein.

The natural wine objection: Fining adds an external substance to the wine, removes some portion of the wine's natural compounds, and (for animal-derived finings) requires disclosure in some jurisdictions. Natural wine movement defaults to unfined.

Filtration

Mechanical removal of particles (yeast cells, bacteria, sediment, cloudiness).

Types:

• Earth filtration (diatomaceous earth / kieselguhr): Course filtering through filter cake. Removes large particles.
• Plate and frame / pad filtration: Paper or fibrous pads catch increasingly fine particles. Sterile filtration (0.45 micron membrane) removes all microorganisms — wine is biologically stable without SO₂.
• Cross-flow filtration: Tangential flow membrane system. High-volume continuous filtration.

The filtration debate: Many serious producers — and the natural wine movement universally — argue that filtration strips wine of character, removes complexity, and homogenizes the texture. The scientific evidence suggests that sterile filtration does remove some large-molecule flavor compounds along with the particles. Whether the difference is detectable or significant is the question.

• Most Burgundy grand cru: unfined and unfiltered (or very lightly filtered)
• Most commercial wine: filtered for stability and clarity
• Middle ground: light filtration (coarse earth filter only) that removes cloudiness without stripping character

Sulfur Dioxide (SO₂)

What It Does

SO₂ (sulfur dioxide) serves two simultaneous functions in winemaking:

1. Antioxidant: Binds with oxygen and its reactive derivatives (acetaldehyde, hydrogen peroxide), preventing oxidation of the wine's aromatic compounds and phenolics.
2. Antimicrobial: Free SO₂ (the portion not bound to other compounds) inhibits bacteria and wild yeast at sufficient concentrations, preventing refermentation in bottle and bacterial spoilage.

The molecular SO₂ concept: Only free SO₂ (particularly the molecular form, highest at lower pH) is antimicrobial. Most SO₂ added to wine binds rapidly with acetaldehyde, aldehydes, and sugars (bound SO₂). Winemakers target free SO₂ levels, not total SO₂.

When It Is Used

• At harvest: Prevents oxidation and wild yeast/bacterial activity during transport to winery
• During fermentation: Generally not used (yeast outcompetes most threats; CO₂ blanket provides protection)
• After MLF: Critical window — once MLF is complete, residual malic acid is gone, bacterial food source is reduced, but the wine is vulnerable to Brettanomyces and acetic acid bacteria if not protected
• At bottling: Final SO₂ addition to protect wine during distribution and aging

Legal maximums (EU):

• Dry red wine: 150 mg/L total SO₂
• Dry white wine: 200 mg/L total SO₂
• Sweet wines: Higher limits (to compensate for residual sugar's SO₂ binding)
• "Organic wine" EU designation: 100 mg/L red, 150 mg/L white (lower limits are the defining regulation)

The Natural Wine Debate

Natural wine position: SO₂ addition is a chemical intervention that reduces wine's natural character. Wines made without addition (zéro-zéro in French natural wine vocabulary) are more alive, more expressive, more terroir-transparent. The fragility is a feature — if you're drinking a living wine, it needs to be treated accordingly (temperature-controlled transport, careful storage, consumption within a realistic window).

Conventional wine position: SO₂ is one of wine's longest-used preservatives (used since ancient Roman times in the form of burning sulfur wicks inside amphoras). At approved levels, the risks are minimal (except for the small percentage of people with SO₂ sensitivity — typically relevant only at high doses, mostly from cheap wine where much larger quantities are used). Without adequate SO₂, wines are unstable during transport, in retail environments, and in consumers' homes — most people don't cellar wine properly. Responsible SO₂ use protects the consumer's experience.

The reality: Both positions contain truth. Natural, zero-SO₂ wines from skilled, clean winemakers can be extraordinary. Natural, zero-SO₂ wines from careless or poorly-equipped winemakers can be faulty (volatile acidity, mousy, oxidized). The binary "SO₂ good vs SO₂ bad" debate ignores the technical nuance that makes the difference between those two outcomes. The question is not whether SO₂ is used but how much, when, and for what reason.