Winemaking Processes: Protein Stability, Fermentation & Sparkling Wine
Identifying Protein Instability in Wine
To differentiate protein instability (protein haze) from other issues like iron casse, perform the following tests:
- Add a few drops of hydrochloric acid to the cloudy wine. If protein instability is present, the cloudiness will likely increase.
- Alternatively, heat the wine to 80°C. If the haze dissolves, it might be tartrate crystals or another deposit. If it persists or increases, protein instability is likely. [Note: Standard tests often involve heating to induce haze if unstable proteins are present. The text describes dissolving, which is less typical for protein haze itself but might differentiate it from other heat-soluble deposits.]
White Wine Fermentation Process
Fermentation for white wines typically takes place at lower temperatures than for red wines (e.g., 20°C or lower, often 12-18°C) to preserve delicate secondary varietal aromas. Additionally, the aromas produced by yeasts at higher temperatures might be less desirable for some white wine styles compared to those typical in red wine vinification.
White must often has fewer indigenous yeasts after settling (racking), which can delay the spontaneous start of fermentation. Therefore, fermentation is often initiated using:
- A pied de cuve: A starter culture prepared by fermenting a small quantity of must, which is then added to the main batch (often placed at the bottom of the tank before filling).
- Selected active dry yeast (ADY).
Whether malolactic fermentation (MLF) is encouraged or blocked depends on the desired wine style; it is often prevented in white wines to maintain higher acidity.
Sparkling Wine Production Methods
Sparkling wines contain carbon dioxide (CO2) from a natural, endogenous origin. This CO2 can come from the primary alcoholic fermentation (ancestral method) or, more commonly, from a secondary fermentation of a base wine.
Common types include Champagne, Cava, and other sparkling wines made via natural fermentation in bottles (traditional method, transfer method) or large tanks (Charmat method). They typically involve adding sugar and yeast (liqueur de tirage) to a base wine to induce a second alcoholic fermentation, which produces the characteristic bubbles.
Traditional Method Stages
1. Tirage Bottling
The base wine is bottled with the liqueur de tirage (a mixture of sugar dissolved in wine, plus yeast). The bottles are sealed with a temporary closure, often a crown cap with a plastic cupule (bidule).
2. Second Fermentation & Lees Aging (Prise de Mousse & Sur Lie)
Bottles are stacked horizontally (sur lattes or en tirage). The second alcoholic fermentation, or prise de mousse, occurs inside the bottle, typically lasting 1-2 months at cool temperatures (10-15°C). A slow fermentation enhances foam quality. Afterward, the wine ages sur lie (on the lees – spent yeast cells). During this aging period (minimum 9 months for many appellations, often much longer, e.g., 3-8+ years for prestige cuvées), yeast autolysis occurs. This process releases amino acids and other compounds that contribute complexity, flavour, and finer bubbles. For extended aging, bottles may be periodically shaken (poignettage) to prevent lees from sticking.
3. Riddling (Remuage)
To collect the lees in the neck of the bottle, riddling (remuage) is performed. Bottles are gradually rotated and tilted from horizontal to an inverted vertical position (sur pointe). This process settles the yeast sediment into the neck, leaving the wine clear.
4. Disgorgement & Dosage (Dégorgement & Liqueur d’Expédition)
The collected lees are removed through disgorgement (dégorgement). The neck of the inverted bottle is typically frozen in a brine solution (around -25°C). When the temporary cap is removed, the internal pressure expels the frozen plug of yeast sediment. A small amount of wine is lost, which is replaced by the liqueur d’expédition (or dosage). This is a mixture of wine and sugar, determining the final sweetness level:
- Extra Brut (driest)
- Brut
- Extra Dry
- Dry (Sec)
- Semi-Dry (Demi-Sec)
- Sweet (Doux) (sweetest)
5. Corking & Dressing
The bottle is then sealed with a final cork, secured with a wire cage (muselet). The bottle is ‘dressed’ with labels and foil. The producer’s name and product type are typically indicated.
Note on Transfer Method: Fermentation and initial aging can occur in the bottle, after which the wine is transferred under pressure to a tank to remove lees via filtration before final bottling. The initial bottle fermentation phase might last around two months.
Tank Method (Charmat) Sparkling Wines
For some sparkling wines, the second fermentation takes place in large, pressurized, airtight tanks (cuve close). After fermentation (which can be relatively short, e.g., ~21 days or longer depending on quality level), the wine is filtered and bottled under pressure.
Cava vs. Champagne Distinction
Cava is a Spanish sparkling wine produced using the traditional method, primarily in the Penedès region of Catalonia, but also in other designated areas of Spain. The term ‘Cava’ designates this specific Spanish Denominación de Origen (DO).
While made using the same traditional method, the term ‘Champagne‘ is legally protected and reserved exclusively for sparkling wines produced under strict regulations within the Champagne wine region of France.