Elevators, conveyors and hoppers

A hopper is a holding volume with a controlled outlet. Its job is to accept a whole bin at once and release fruit at the rate the next machine can take it, which decouples the delivery from the process and means a mill can run continuously while fruit arrives in batches. That is the entire idea, and most of what goes wrong with a mill intake is a hopper problem rather than a mill problem.

Fruit bridges. A mass of apples in a converging hopper can arch across the outlet and hold itself up, so the mill runs empty while the hopper is full — and the standard response, poking at it with something, is exactly the action that causes injuries. Hoppers designed for fruit have a wide, steep outlet, a slow-turning agitator or a live bottom, and vibration or an air blast to break an arch without anyone touching the fruit.

Feed rate also matters for the mill itself. Choke feeding — keeping a mill full so that fruit is worked against fruit — gives a different pomace from a starved feed where each apple meets the rollers alone, and a hammer mill fed unevenly produces a grind that shifts through the day. Level control on the hopper is therefore a quality device as much as a convenience.

The auger row is the one that surprises people. An auger is cheap, compact, self-emptying and will move almost anything, and it is a poor way to move whole apples because the flight shears fruit against the trough wall and produces a mash before the mill has seen it. It is the standard way to move pomace away from a press, which is a different problem entirely: the material is already broken and the shear does not matter.

Damage happens at transitions rather than along conveyors. A belt discharging onto another belt, an elevator tipping into a hopper, a chute ending on a steel plate — these are where the drop height is, and the energy in a falling apple goes into bruising it. Well-arranged plants keep free-fall heights short, fit deceleration plates or brush curtains at drop points, and let fruit land on fruit or on water rather than on metal.

How much this matters depends on what happens next. A bruise is a broken cell wall, polyphenol oxidase meeting its substrates, and the beginning of oxidation — which for cider fruit going into a mill twenty minutes later is largely irrelevant, and may even be part of the character being sought. It becomes serious in two cases: fruit that will be held for days before milling, where a bruise is where rot starts, and juice intended to be pale and aromatic, where every bit of early oxidation is a subtraction.

The other consideration is entirely practical. Bruised and split fruit sheds juice onto the conveyor, and juice on a belt is sticky, attracts vinegar flies and feeds an acetic population that is then in contact with every subsequent load. Conveyors are washed down during the day and not just at the end of it.