macération pelliculaire in French, winemaking operation with the aim of extracting flavour compounds, flavour precursors, and anthocyanins from grape skins into grape juice or wine. In its widest sense, it is identical to maceration, and some form of skin contact is usually essential to rosé winemaking, but the term is generally used exclusively for the maceration of white grapes for about four to 24 hours before pressing and fermentation with the aim of increasing the extraction of constituents that contribute to the aroma of white wines. Destemmed and moderately crushed grapes are put into a vat and covered with inert gas and cooled down, if necessary, to a temperature of less than 15 °C/59 °F. A few hours later, the free-run juice is collected and the marc is pressed. Skin contact can also take place directly in airtight pneumatic presses. Skin contact tends to reduce must acidity and increase ph. It also increases the concentration of amino acids, leading to a better rate of fermentation. Vine varieties frequently processed with skin contact are Sémillon, Sauvignon Blanc, Gros Manseng, Muscat, and Riesling. Grapes must be healthy, fully ripe, and have sufficient acidity and low tannin content. Denis dubourdieu and his team have been responsible for its application to white bordeaux since the late 1980s. It is important to arrest skin contact before excessive amounts of bitter phenolics (which may also darken colour) are extracted. In some vintages and in some regions, especially when the skin is rich in tannin due to a hot, dry climate, the technique simply does not work as too much undesirable material is extracted with the minimum amount of additional flavour compounds.