In cidermaking, pre-filtering typically takes place after pressing to remove pectin and, though not as common in winemaking, it is sometimes done while racking the wine. The purpose is to remove visible sediment from the juice prior to depth filtering to avoid clogging up (and wasting) filter media. This is typically done with a bag filter, as filter bags that have a much higher porosity than depth filter media. Another method is a pipe screen filter, which uses a pair of inline filter screens that can either be used simultaneously or one at a time—allowing for continuous operation, as one screen is in use while the other is being cleaned, then the flow can be diverted to the clean screen while the first is removed and cleaned.
