Sparkling Wine Production and Protein Stability in Wine
Protein Stability in Wine
Protein Bankruptcy
Protein bankruptcy occurs when grape proteins and yeast in wine coagulate due to heat, cold, or tannins from oak aging or cork stoppers. This results in a haze that starts below the cap and spreads throughout the bottle when agitated. Red wines are less susceptible due to tannins binding with proteins during barrel aging. White wines, however, retain proteins that need removal before bottling.
Treatment
Bentonite, a negatively charged clay, is used to remove proteins. It attracts positively charged wine proteins through electrostatic adsorption. Bentonite is available in powder or granular form, swelling tenfold in water to form a colloidal gel with a large surface area for adsorption. It should be hydrated in cold or warm water for 24 hours, stirred into a gel or paste, and then added slowly to the wine while stirring for 5-10 minutes.
Heat Test
To assess protein stability, fill a test tube with wine, add a touch of tannin, stir, and heat in a water bath at 80°C for 30 minutes. Cool in a refrigerator for 4 hours. If the wine remains clear, there’s no risk of protein bankruptcy. A whitish haze or deposit indicates the presence of proteins and potential instability. Tannin is used to promote protein precipitation and flocculation. A nephelometer can also detect protein presence.
Identifying Protein Bankruptcy
To differentiate protein haze from iron deposits, add a few drops of hydrochloric acid to the cloudy wine. Increased turbidity indicates protein bankruptcy. Heating to 80°C will solubilize the protein if it’s the cause of the haze.
Sparkling Wine Production
Sparkling wines contain CO2 from natural or endogenous sources, either from the initial grape fermentation or a secondary fermentation of a base wine. Examples include Champagne, sparkling wine produced through natural fermentation in bottles or large containers. All share a common process: sugar and yeast are added to a base wine to induce a second fermentation, creating the characteristic bubbles.
1. Naturally Fermented Sparkling Wine and Champagne
Champagne, produced using the traditional method (méthode champenoise), undergoes secondary fermentation and aging on lees in the bottle, followed by riddling and disgorgement. Cava, a Spanish sparkling wine with a Denominación de Origen (DO), is made similarly. Both use white grapes (Macabeo, Viura, Xarel-lo, Chardonnay, Parellada) and sometimes red grapes (Garnacha, Monastrell, Pinot Noir, Trepat).
Preparation Phases
- Tirage: Bottled wine receives a liqueur de tirage (sugar and yeast mixture). Bottles are sealed with a temporary crown cap.
- Second Fermentation and Aging: Bottles are stacked horizontally for 1-2 months at 10-15°C. Slow fermentation enhances foam quality. Aging on lees (dead yeast cells) follows, lasting at least 9 months and up to 5-8 years for premium cuvées. Periodic riddling prevents yeast adherence to the bottle.
- Riddling (Remuage): Bottles are gradually rotated and tilted until inverted, collecting the lees in the neck.
- Disgorgement (Dégorgement) and Dosage: The neck is frozen, and the lees plug is expelled. A liqueur d’expédition (sugar solution) is added to determine sweetness levels (extra-brut, brut, etc.). Bottles are corked and labeled.
2. Bottle-Fermented Sparkling Wine (Transfer Method)
Similar to the traditional method, but after fermentation and aging, the wine may be transferred to a new bottle to remove the lees.
3. Sparkling Wine in Large Containers (Charmat Method)
Secondary fermentation occurs in a large, sealed tank. The wine is then filtered and bottled under pressure. This process is faster, typically taking 21 days from yeast addition to bottling.