Six things that ruin a batch

Every one of these is common, and every one is free to fix. They are in rough order of how often we hear about them.

1. Overlapping slices

Pieces touching or stacked trap moisture between them. That part of the tray stays wet while everything around it finishes, and the batch either goes back in and over-dries or comes out with a few pieces that will spoil the bag. Lay everything flat with a gap.

2. Uneven thickness

A tray of mixed thicknesses finishes three times over. Even thickness matters more than thin — 5–6 mm, consistently, beats a tray that ranges from 3 mm to 10 mm.

3. Turning the heat up to save time

This is case-hardening, and it is the expensive one because the batch looks finished. A dry shell forms over a wet centre, the moisture redistributes in storage, and the product spoils a fortnight later. Fruit at 55–60 °C and no higher.

4. Sealing it while it is warm

Warm food in a sealed container condenses, and the water goes straight back in. Cool to room temperature first.

5. Never rotating the trays

Even in a well-designed cabinet the trays nearest the fan finish first. One rotation around the halfway point costs a minute and evens out the whole run.

6. Judging doneness by the surface

The outside of a slice is always drier than the inside. Tear a thick piece in half, let it cool, and look at the centre. That is the only test that tells you anything.