Slice thickness: the one variable beginners get wrong

Twelve to fifteen millimetres for most foods. Thickness is the single variable that decides your cycle length, and getting it wrong is the most common reason a batch comes out with a wet centre while the edges are crisp.

Why it matters more than anything else

Water vapour has to travel from the middle of a piece of food to its surface before it can leave. That journey gets disproportionately harder as the piece gets thicker — doubling the thickness more than doubles the drying time, because the path is longer and the outer layer, now dry, insulates the wet core.

This is also why a tray finishes at the pace of its thickest piece. Uniformity matters as much as the number.

Thickness by food

Food	Thickness	Note
Strawberries, soft fruit	10–12 mm	Halve small ones, slice large
Apple, pear	10–12 mm	Corer and mandoline give consistency
Banana	8–10 mm	Dense and sugary; thinner than you think
Cooked meals	12–15 mm layer	Spread, do not mound
Raw meat	10–12 mm	Slice against the grain, partly frozen
Cooked meat, shredded	Loose single layer	Do not compact it
Peas, sweetcorn	As they are	Already the right size
Cheese, grated	Loose layer	Grating is the slicing
Milk, liquids	8–10 mm depth	Depth in the tray, not thickness
Candy	As it is	Single layer, on mats

The tools that make it consistent

You do not need much, but a knife alone makes consistency hard over five trays.

• A mandoline is the single most useful prep tool for this. Set once, and every slice matches.
• An egg slicer handles strawberries surprisingly well.
• A food processor with a slicing disc for volume, though it is less precise.
• Partial freezing before slicing makes meat and soft cheese far easier to cut evenly.

Depth versus thickness for liquids

Milk, yoghurt, puree and sauce do not have a thickness, they have a depth in the tray. Eight to ten millimetres is the working figure — deeper and the middle takes forever. This is where silicone mats earn their place, because they let you lift a dried disc out intact.

What too thick looks like when it fails

The batch feels finished. The edges snap, the surfaces are dry, the machine has ended its cycle. Then three months later the bag has gone soft, because the centre of the thickest pieces held moisture that redistributed through the sealed bag over time.

That is the failure mode, and it is why the weight test matters: weigh a test tray, run two more hours, weigh again. If the weight is still dropping, thickness is probably why.