Components of Must
Must consists of:
- Juice — water, sugars (glucose and fructose), acids (tartaric, malic, citric), and flavour precursors
- Skins — source of colour, tannins, and aromatic compounds
- Seeds — contain bitter tannins released with excessive pressing
- Stems — can add green tannins or, in whole-cluster fermentation, provide spice and structure
Must Weight
Must weight measures the sugar concentration of the juice and predicts potential alcohol. Common scales include Brix (USA), Baumé (France/Australia), and Oechsle (Germany). A must at 24° Brix will produce approximately 13.5% alcohol.
Must Treatments
Before fermentation, winemakers may adjust must through:
- Chaptalization — adding sugar to raise potential alcohol (common in cool climates)
- Acidification — adding tartaric acid in warm climates where grapes lose acidity
- Cold settling — allowing solids to settle before fermentation for cleaner juice
- Saignée — bleeding off some juice to concentrate the remaining must for red wines