Chapter 11

Wine Filtration

The Right Filter for Each Application

Filtration is primarily used in winemaking to achieve two goals: to attain an acceptable level of clarity and to improve microbial stability. Proper filter selection means choosing the right filter for a given purpose. There are appropriate situations for specifying nominal versus absolute high beta-ratio filters. Depth filters (e.g., pressure leaf, plate and frame, and lenticular) and cross-flow filters on the lower end of the performance spectrum provide clarification (solids removal, turbidity reduction), and some protection of downstream particle filters, with nominal filters of fixed pore construction providing much improved protection.

Turbidity and Filterability

When deciding which approach to take with filtration measuring the turbidity and filterability is a useful tool. The two measurements which are usually used in this regard are nephelometric turbidity units (NTU) and filterability index (FI).

Turbidity

Turbidity is the degree of clarity or haziness of wine. Wines just after fermentation contain both large and small suspended solids, including yeasts, bacteria, protein or pectin complexes, phenolic complexes, and metal precipitates and are often well above 200 nephelometric turbidity units (NTUs). Wines at this stage are usually settled, fined, and stabilized to improve clarity. Wines between 100 and 200 NTUs may undergo filtration steps from coarse metal screens to diatomaceous earth (DE) filtration, with a finer DE filtration conducted between 60 and 100 NTU.

Filterability Index

The filterability index (FI) of a wine is an indication of the time needed to block a specific filter medium during filtration. One simple method is to record the time which is required to filter respectively 200- and 400-mL wine with the chosen membrane at a constant pressure of 2 bar.

Click on the following topics for more information on wine filtration.