What the press does to the juice

A mill breaks cells. Juice sits inside cell walls, and until those walls are ruptured no amount of pressure will release it — which is why whole fruit under a press yields almost nothing and why the mill, not the press, sets the ceiling on extraction.

Particle size is the variable, and it has an optimum rather than a direction. Too coarse and a large fraction of cells survive intact, so the juice stays in the pomace. Too fine and the pomace becomes a paste with no internal drainage channels: juice released at the centre cannot reach the surface, the pomace blinds the cloth or the press surface, and yield falls even though more cells were broken. Every press has a pomace texture it works best with, and matching the mill to the press is a real decision rather than a detail.

Fruit condition interacts with this. Firm fruit grates into discrete particles; over-soft fruit smears, and a mill set correctly for sound fruit produces paste from fruit that has been held too long. This is one of the practical reasons the maturity decision and the pressing decision cannot be taken separately.

Once the fruit is milled, the clock starts. Pomace left standing before pressing continues to release phenolic material and colour into the juice, and enzymes released from the broken cells begin working on the pectin. Held deliberately, this is maceration; held accidentally, it is the same process without a decision behind it.

What it gains is extraction: more phenolic material, more colour, and often more juice, because the pectin degradation makes the pomace release liquid more readily. What it costs is oxidation. Polyphenol oxidase, released at the same moment as everything else, converts phenolic compounds in the presence of air, and the same phenolic material that maceration is extracting is the material oxidation is consuming.

Maceration is not keeving, and the two are confused constantly. Maceration is a pre-press hold of the pomace to extract more from it. Keeving is a post-press process in which pectin is deliberately gelled in the juice so that it floats, taking nutrients and solids with it, in order to starve the ferment. They happen at different stages, use different mechanisms and have opposite intentions with respect to nutrient content.

Batch presses — rack and cloth, basket, hydraulic — build a stack or a load, apply pressure, and take it apart afterwards. Continuous presses — belt presses in particular — run pomace through moving surfaces without stopping. The mechanical difference is one of process, and the consequence for the juice is one of air.

A rack-and-cloth cheese is a largely sealed stack: the juice inside it is surrounded by pomace rather than by atmosphere, and it drains out at the edges. A belt press spreads pomace in a thin layer between two open belts, which is exactly the geometry that maximises air contact — a large surface area, in the open, for the whole of the pressing. That is the trade, and it is a trade rather than a defect: the belt press is the reason commercial cider making is possible at scale, and oxidation before fermentation is not always unwanted.

The bladder press is the interesting case because it is closed. An inflatable membrane presses pomace against the walls of a sealed drum, which can be flushed with inert gas or simply kept shut, so the juice can be recovered with very little oxygen contact at moderate speed. That combination is why bladder presses have spread through small commercial cider making despite being expensive.

Yield numbers for presses are quoted freely — sixty per cent for a hand press, seventy-five for a hydraulic, higher for a belt — and almost all of them trace to equipment marketing rather than to a trial. CiderHQ has not found a published comparative trial pressing the same fruit, milled the same way, through several press types.

That absence matters because the figures are not comparable even in principle unless the fruit and the milling are held constant. Juice yield depends on the cultivar, on how ripe the fruit was, on how finely it was milled and on whether it was macerated, and any of those moves the number by more than the difference between two presses does.

What can be said without a trial is the ordering of the trade — speed against oxygen — and that is what the figure above shows.

Pomace after pressing still holds liquid. Rehydrating it and pressing again — historically ciderkin or water-cider, and still done commercially as a second extraction — recovers a weak juice that carries a disproportionate share of the remaining phenolics and very little sugar.

What that liquid may then be called is a regulatory question rather than a technical one, and it differs by jurisdiction. In the United Kingdom and in most European frameworks the juice content of the finished product is what the label has to reflect; in the French appellations of origin, added water is simply forbidden, while the two French geographical indications permit it.