The trap filter system is designed to capture any solid particulate such as filter aids which may remain in the wine following primary clarification. The objective of this stage is to provide a consistent level of particulate filtration to help reduce filterability index and provide clear wine to intermediate storage.
Potassium bitartrate and calcium tartrate crystals are naturally occurring precipitates in wine which form non-hazardous, glass-like crystals as the alcohol concentration increases during must fermentation. These crystals are undesirable as they are sometimes large enough to be visible to the naked eye (>40μm) and need to be removed during production. To remove the crystals, the wine is chilled to just above freezing point, facilitating crystallization and precipitation, and the crystals can then be removed by filtration.