Red Winemaking Process: From Grape to Glass

Posted on Jul 2, 2024 in Biology

Red Winemaking:

The process of red winemaking involves fermenting the wort (grape juice) with the solid parts of the harvest (skins and seeds). This extraction process imparts color, flavor, and mouthfeel to the wine.

Operations Before Vinification:

Collection and Transport:

Harvesting grapes carefully is crucial to ensure the clusters arrive intact and prevent premature fermentation. Here’s how:

  1. Minimize transfers.
  2. Prevent grapes from being crushed.
  3. Use easy-to-clean containers to avoid contamination.
  4. Employ inert containers to prevent unwanted reactions.
  5. Minimize impurities like dust and dirt.
  6. Keep harvest, transportation, and unloading time short.

Reception in Bodega:

Upon arrival at the winery, several operations take place:

  1. Weighing: This can be done using a double-weighing method (weighing the trailer with and without the load) or a single-weighing method (weighing the grapes directly).
  2. Sampling: Samples are taken to determine grape price based on maturity and classify the harvest quality. Automated analyzers measure sugar, pH, total acidity, and harvest rot.
  3. Unloading: Grapes are carefully unloaded into a discharge chute or directly into the processing machinery to maintain their integrity.

Mechanical Treatment of the Grape:

1. Crushing:

Crushing breaks the grape skins to release the pulp and juice. Gentle crushing is essential to avoid damaging seeds and skins. Advantages of crushing include:

  • Easier transport of the must
  • Improved skin contact
  • Yeast dispersion and aeration
  • Facilitation of maceration in red wines
  • Enhanced extraction of anthocyanins and tannins
Types of Crushers:
  1. Roller Crushers: These use two rotating rollers to gently crush the grapes.
  2. Centrifugal Crushers: These machines combine crushing and destemming. Grapes are fed into a rotating drum with paddles that force them against a perforated grid, separating the stems from the crushed grapes.

2. Destemming:

Destemming separates the berries from the stems and can be done before or after crushing. Advantages in red winemaking include:

  • Improved taste
  • Slightly higher alcohol content
  • Higher color concentration during maceration
  • Space savings

However, destemming can also lead to difficulties in pressing, slower fermentation, and increased oxidation in poor harvests.

Types of Destemmers:

Destemmers typically consist of a rotating horizontal drum with perforations. As the grapes move through the drum, the stems are separated and ejected.

3. Maceration:

After crushing and destemming, the must is transferred to fermentation tanks. During maceration, the must is in contact with the grape skins, extracting color, tannins, and flavor compounds.

4. Maceration Process:

During maceration, polyphenols and aroma compounds are extracted from the solid parts of the grapes.

5. Alcoholic Fermentation:

Alcoholic fermentation is the process of converting sugar into ethyl alcohol and carbon dioxide. This process is carried out by yeast, primarily Saccharomyces cerevisiae, naturally present on the grapes. Fermentation typically lasts 10-15 days and has two phases:

  1. Tumultuous Fermentation: This phase lasts 8-10 days and is characterized by high yeast activity, rapid sugar decline, temperature increase, and significant carbon dioxide release.
  2. Slow Fermentation: This phase sees reduced yeast activity, slow density decline, stable temperature, and minimal carbon dioxide release.
Monitoring Fermentation:
  1. Density: Measured using a hydrometer, density indicates the sugar concentration in the must. It typically decreases from 1.100 to 0.994-0.996 during fermentation.
  2. Temperature: Maintaining optimal temperature (28-30°C for aged wines, 19-25°C for young wines) is crucial for yeast activity and preventing unwanted flavor compounds.

Temperature control is achieved using stainless steel tanks equipped with cooling jackets, showers, or heat exchangers.