Pre-freezing the load overnight in a normal freezer shortens the cycle noticeably and reduces wear on the compressor, because the machine skips most of the freeze-down phase. It is the easiest saving available and it costs you nothing but planning.
What the machine does without it
Load room-temperature food and the first phase of the cycle is the machine taking it from ambient down to around −30°C. That is the hardest work the compressor does, it draws the peak power of the whole cycle, and it happens before any drying starts.
Load food that is already at −18°C from a domestic freezer and most of that work is already done. The machine still needs to take it colder, but the bulk of the temperature drop has been achieved by an appliance you already own and pay to run anyway.
What it saves
- Cycle time. Owners commonly report several hours. The exact figure depends on the load and your machine.
- Peak electrical draw. The freeze-down phase is when a machine pulls closest to its maximum. Skipping it keeps the average lower.
- Compressor wear. Less time at maximum load. On a machine you intend to keep a decade, this is worth having.
- Better ice crystal structure, arguably. A domestic freezer freezes more slowly than a blast freeze, which makes larger crystals — so this one cuts both ways. See below.
The one argument against it
Slower freezing makes larger ice crystals, and larger crystals do more damage to cell walls. Machines with a circulating fan blast-freeze deliberately to get small crystals and better texture. So pre-freezing in a domestic freezer may cost you a little texture quality on delicate foods.
In practice this is a small effect and most owners cannot detect it. If you are drying premium fruit for sale and texture is your selling point, load fresh and let the machine blast-freeze. For everything else, pre-freeze.
How to do it well
- Load the trays first, then freeze them. Freezing food in a bag and transferring it later means handling frozen food and losing the even layer.
- Stack trays with spacers if your freezer is tight, so air can circulate.
- Overnight is enough. Twelve hours is plenty; longer does no harm.
- Move fast at transfer. Trays out of the freezer and straight into the chamber. A few minutes of thawing undoes some of the benefit.
- Do not pre-freeze liquids you poured to depth unless the tray is level in the freezer, or you will get a wedge.
If your freezer is full
This is a genuine constraint and the reason many owners skip it. One workaround is to pre-freeze only two or three trays and load the rest fresh – you still get part of the benefit.