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Equipment

Filters: plate, sheet, cartridge and crossflow

What kinds of filter are used on cider and what does each remove?

In short

Depth filters — sheets, pads and diatomaceous earth beds — trap particles throughout a thick porous layer. Surface or membrane filters — cartridges and crossflow modules — retain particles on a defined pore structure at the surface.

The important distinction for a cider maker is between clarifying filtration, which makes a cider bright, and sterile filtration, which removes viable organisms so that a sweetened or unsulphited cider will not referment in the bottle.

Every filtration removes something besides haze. Colour, colloidal body and some aroma go too, and the finer the filtration the more of them go.

The equipment families

Sequence matters more than any single choice. A fine filter fed with turbid cider blinds almost immediately, so filtration is done in steps of decreasing pore size, with settling, fining or centrifugation ahead of it. Attempting to take a hazy cider straight to a sterile cartridge wastes the cartridge and does not achieve sterility.

Filter types and what they are for
TypeMechanismTypical purposeMain drawbacks
Sheet or plate-and-frame filterDepth filtration through cellulose sheets of graded tightnessRough clarification through to near-sterile polishingSheets are single-use; can strip flavour; rinsing needed to remove paper character
Diatomaceous earth or kieselguhr filterA bed of filter powder built on a support and dosed continuouslyHigh-throughput clarification of turbid liquidRespirable crystalline silica hazard in the dry powder; spent earth is a waste stream
Lenticular moduleStacked depth media in a sealed housingClarification with less handling than loose sheetsConsumable cost
Cartridge filterPleated membrane or depth medium in a housing, rated nominal or absoluteFinal polishing and sterile filtrationBlinds quickly if fed unclarified cider; must be integrity-tested for sterile duty
Crossflow or tangential filterCider flows across a membrane surface rather than into it, so the retained material is swept awaySingle-step clarification without filter aidHigh capital cost; can strip colour and aroma; demanding cleaning regime

Nominal, absolute and what "sterile" means

Filter ratings come in two kinds. A nominal rating states a size that the filter retains most of, which is a statistical statement and gives no guarantee about any individual particle. An absolute rating states a size above which retention is essentially complete, established by a defined challenge test. For anything that matters microbiologically, only an absolute rating means anything.

Sterile filtration in beverage work generally means membrane filtration at a rating capable of retaining yeasts and the bacteria of concern, with the filter integrity-tested before and after use so that a failure is detected rather than assumed away. It is not a matter of buying a cartridge with a small number on it; it is a validated process with a downstream that must also be sterile, because a sterile-filtered cider filled through a contaminated filler is not sterile.

This is the whole point of sterile filtration for cider: it is the alternative to pasteurisation and to chemical stabilisation for a product that contains fermentable sugar and must not referment. A cider that has been back-sweetened and is going into a sealed bottle either has its yeast removed, killed, or inhibited — and the consequences of getting that wrong are pressure in glass, not merely a spoiled flavour.

What filtration costs the cider

Depth filter sheets carry a charge as well as a pore structure, and they adsorb material electrostatically as well as sieving it. That is why a tight sheet filtration can noticeably lighten colour and reduce phenolic content, and why a heavily filtered cider often tastes thinner than the same cider unfiltered. It is also why sheets are rinsed thoroughly before use: unrinsed cellulose contributes a papery character that is immediately recognisable.

Crossflow membranes strip differently. Because the membrane retains everything above its cut-off, colloids and larger aroma-bearing complexes are removed, and producers report a loss of body and of some aromatic lift. Modern membranes and gentler operating regimes have narrowed this, and it has not disappeared.

The judgement is a stylistic one and the site takes no position on it. A bright, stable, filtered cider is a legitimate product and so is a naturally settled cloudy one. What is not legitimate is filtering to a rating that does not achieve microbiological stability and then treating the cider as though it were stable.

Filter aid dust

Diatomaceous earth and perlite filter powders can contain crystalline silica, and inhaling the dry dust is a genuine occupational lung hazard. Handling requires the supplier’s guidance, dust control at the mixing point and appropriate respiratory protection. Spent filter earth is also a disposal question with its own local rules.

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