Fermentation on the Skins

Definition

Fermentation on the skins (German: Maischegärung) refers to the fermentation process in which the must ferments together with the solid grape components (skins, seeds, and sometimes stems). This process is characteristic of red wine production and is decisive for the development of color, tannin structure, and the aromatic spectrum.

The Process in Detail

Preparation

After harvest, the grapes are destemmed (stems removed) and lightly crushed or ground. The result is the must mass (Maische) — a mixture of juice, skins, seeds, and possibly stems. This mass is filled into fermentation vessels.

Fermentation

Alcoholic fermentation is triggered by yeasts — either by natural yeasts on the grapes (spontaneous fermentation) or by added cultured yeasts. During fermentation:

• Sugars are converted into alcohol and CO₂
• The skins are pushed upward by the forming CO₂ and create the cap (French: chapeau)
• The skins must be regularly brought back into contact with the must

Extraction During Fermentation

The most important substances extracted from the skins during fermentation on the skins:

Color compounds (anthocyanins) are found in the skins of red grapes. Extraction occurs mainly in the first 3–5 days of fermentation. The developing alcohol acts as a solvent and intensifies color extraction.

Tannins come from skins, seeds, and stems (if included). They give the wine structure, aging potential, and the characteristic mouthfeel. Tannin extraction is time-dependent and increases with longer maceration time.

Aromatic compounds from the skins contribute significantly to the flavor profile. Primary fruit aromas, but also more complex notes, are released during fermentation on the skins.

Techniques for Fermentation on the Skins

Submerging the Cap

To ensure optimal extraction, the cap must be regularly brought into contact with the fermenting must:

Pigeage (punch-down): A traditional method in which the cap is pushed down mechanically or by hand into the must. This was formerly done by hand with wooden poles, but today is mostly mechanical.

Remontage (pump-over): The must is drawn off from below and pumped over the cap. This method is less oxidative than pigeage and allows for gentler extraction.

Délestage (rack and return): The entire must is drained off, the cap collapses, and the must is then pumped back in. This leads to more intensive extraction and better oxygen uptake.

Temperature Control

Fermentation temperature significantly influences extraction:

• Cooler fermentation (22–26°C): Emphasizes fruity aromas, gentler tannin extraction, lighter color
• Warmer fermentation (28–32°C): More intensive color extraction, stronger tannins, more complex aromas
• Cold maceration: Before fermentation, the must mass is kept cool (10–15°C) for several days to extract color and aromas without alcohol

Duration of Fermentation on the Skins

The maceration time varies depending on the desired wine style:

• Short fermentation (3–7 days): Lighter, fruit-forward red wines with softer tannins
• Medium fermentation (8–14 days): Classic style with balanced structure
• Long fermentation (15–30+ days): Powerful, tannin-rich wines with high aging potential

After fermentation, the wine is separated from the solids — this is called pressing. The free-run must (free-run wine) is usually finer than the press wine obtained by mechanical pressing.

Difference from White Wine Production

The fundamental difference between red and white wine production lies in the fermentation on the skins:

Red wine: Fermentation with skins (on the skins) → color extraction White wine: Fermentation without skins (juice fermentation) → no color extraction, also possible with red grapes (e.g., Blanc de Noirs)

Exception: Orange wines are white wines made like red wines with fermentation on the skins, which leads to more intense color and tannins.

Influence on Wine Style

The type of fermentation on the skins fundamentally shapes the character of the red wine:

Traditional fermentation on the skins in large wooden vats or stainless steel tanks with moderate extraction yields accessible, fruit-forward wines. This is typical of classic German red wines such as Spätburgunder or Frühburgunder.

Modern Burgundian method with whole-cluster fermentation, cold maceration, and extended maceration time produces structured, complex wines with high aging potential.

Mediterranean method with high temperatures and long maceration time creates powerful, tannin-rich wines as in Barolo or Rioja.

Fermentation on the skins is therefore not just a technical process, but a tool with which winemakers can deliberately shape the character of their red wines.