Reverse Osmosis

Reverse osmosis separation of wine is based on the tendency of smaller molecules to pass through a semi-permeable membrane more readily than larger molecules.

The wine to be treated is recirculated at high pressure through a reverse osmosis system which separates the juice or wine into two flows – permeate and concentrate.

Permeate – the flow containing the low molecular weight components which pass through the semi-permeable membrane

Concentrate – the bulk wine flow which is retained by the membrane and contains almost all of the vinous components

According to the wine composition table below, water passes most readily and other, larger wine components progressively less so. As molecules get larger, there is a point where the passage of a particular sized compound becomes insignificant. This is the 'molecular weight cut-off' (MWCO) of the membrane.

For 'tight' RO membranes, this nominal MWCO is about 90. Water, carbon dioxide, ethanol and acetic acid pass through the membrane into the permeate reasonably easily; lactic acid only marginally and other components hardly at all.

With another, 'looser' membrane type all components pass more readily including more of the larger compounds up to about molecular weight 180.

Which membrane is used will depend on the specific Memstar application.

Some wine components and their molecular weights