Reducing Volatile Acidity

Memstar has successfully used its patented VA reduction process since 1997 to reduce the level of volatile acidity (acetic acid and ethyl acetate) in many millions of litres of clients’ wine while flavour elements and other wine constituents remain essentially unchanged.

Excessive volatile acidity still remains a problem, despite the advances in winemaking technology and practice. Wines with VA levels greater than about 0.6 g/l are less appealing to consumers, often displaying estery, glue-like aromas, diminished fruit flavour, and a sour, ‘spiky’ acid finish.

High VA can lead to stuck or sluggish fermentations and a product that is, in many cases unsaleable, particularly at levels in excess of 1.5 g/l, when the wine may not be sold legally.

Since 1997 the Memstar VA reduction process has been used successfully to treat wines with VA levels higher than 3 g/l as well as significantly improving wines with even minor reductions from 0.8 to 0.6 g/l.

How Does it Work?

The wine to be treated is circulated at high pressure through a reverse osmosis plant to separate a flow of permeate which contains water, alcohol and some of the acetic acid and ethyl acetate to be removed. This is then treated in an anion exchange column where the acetic acid is adsorbed on the charged resin. The treated permeate with the volatile acidity removed is recombined with the bulk of the wine concentrate and returned to tank.

Critical to the success of the Memstar VA reduction process is the use of highly selective reverse osmosis membranes operating under optimum conditions of temperature and pressure. In this application, processing at high pressure (up to 70 bar) is preferable because the membranes perform more selectively than at lower pressure.

This means that virtually none of the desirable wine components (the other acids, anions, sugars, tannins, flavour and colour) pass through the membrane but are retained in the concentrate. They do not come into contact with the ion exchange resin so they cannot be absorbed or contaminated. Very little other acid is lost. Nothing is added to the wine and the volume and alcohol content are not affected.

The process continues for as long as necessary to reduce the volatile acidity to the level desired by the winemaker.

Winemakers’ Questions concerning Memstar processes