WINETECH Technical Yearbook 2021

PRACTICAL IN THE CELLAR | JANUARY/FEBRUARY 2021

The importance of solids in white wine making CHARL THERON: Private consultant KEYWORDS: Solids concentration, turbidity, white wine.

SEEING THAT GRAPES are the raw material for wine, the juice and solids they contain will play a role in the eventual wine. In the case of white wine considerably less skin contact is applied than for red wine and the solids remaining after skin contact will play an important role. The extent of juice clarification in white wine making is one of the first resolutions of winemakers. The solid content of white juice influences the alcoholic fermentation and the malolactic fermentation (MLF) as well as the flavour profile of the resulting wine. The grape characteristics and extraction processes of the grape juice cause a considerable difference in the solid content of the grape juice. Limited information however exists regarding the actual composition of the solids in juice. This causes the resolution concerning its optimal composition to be complicated. The solids of white juice consist of approximately

70% polysaccharides, 8% lipids and 2.5% nitrogen. Minerals, phenolic compounds and pectins contribute the most to the remaining composition. The most grape- based solids have a particle size with a diameter smaller than 2 µm. During alcoholic fermentation the particles become smaller as result of the carbon dioxide movement. After that they tend to flocculate and settle together with the yeast lees. The solids do however have a considerable influence on fermentation. They supply especially lipids and nitrogen for yeast cell development. Lipids are an important component of the cell membrane, which facilitates the yeast cell to resist alcohol at the end of fermentation. Juice with a high solids concentration usually ferments faster. The same applies to the rate of MLF. The solids concentration of juice can be expressed as nephelometric turbidity units (NTU), total wet, dry suspended

A racking pipe and plate can be used to separate clear juice from solids.

WINETECH TECHNICAL YEARBOOK 2021 | 150