Freeze drying fruit and vegetables: prep, blanching and times

Sliced strawberries at 10 to 12 mm are the best first batch there is: forgiving, cheap, and they show you exactly what a finished load looks and sounds like. Fruit is where nearly everyone starts and where the habits that make later batches work get learned.

Why fruit first

Three reasons. It is high in water and low in fat, which is the ideal combination for freeze drying. It is cheap enough that a ruined batch costs nothing. And the finished result is unmistakable — a properly dried strawberry slice snaps with an audible crack, which teaches you the test you will use on everything else.

Fruit by difficulty

Fruit	Prep	Cycle	Note
Strawberries	Slice 10–12 mm	12–20 h	The batch to learn on
Raspberries	Whole	12–18 h	Already the right size
Blueberries	Pierce or halve	16–24 h	Skin resists; pierce or they stay wet
Apple	Core, slice 10–12 mm	16–24 h	Dip in lemon water to stop browning
Banana	Slice 8–10 mm	18–26 h	Dense and sugary; thinner than you think
Mango	Slice 10–12 mm	18–26 h	Fibrous; slice across the fibre
Peach, nectarine	Stone, slice 10–12 mm	18–26 h	Skin on is fine
Grapes	Halve	20–30 h	Whole grapes almost never finish
Watermelon	Slice 12 mm	24–30 h	Very high water; loads the cold trap
Citrus	Slice 5–8 mm	16–22 h	Peel and all – makes excellent garnish

The two prep tricks worth knowing

• Pierce the skin on anything waxy — blueberries, grapes, cranberries. An intact skin is a moisture barrier and the fruit will come out with a wet centre. Halving does the same job.
• Acidulate pale fruit. Apple, pear and banana brown by oxidation while you are slicing. A quick dip in water with lemon juice stops it, and does not affect the drying.

Vegetables: blanch first

This is the one real difference from fruit. Most vegetables should be blanched — briefly boiled, then chilled in cold water — before drying. Blanching deactivates the enzymes that would otherwise keep degrading colour, texture and flavour during storage.

Vegetable	Blanch	Then
Peas	60–90 sec	Chill fully, drain, load
Sweetcorn	2–3 min	Chill, drain well
Green beans	2–3 min	Cut to size first
Broccoli, cauliflower	2–3 min	Small florets
Carrots	2–3 min	Slice or dice 8–10 mm
Potato	3–5 min	Dice; blanching also stops browning
Onion	No need	Dries well raw; strong smell transfers
Peppers	No need	Slice and load
Mushrooms	No need	Slice 8–10 mm
Leafy greens	30–60 sec	Very fast to dry afterwards
Tomato	No need	Slice 10 mm; high water content

The onion warning

Onion and garlic transfer their smell aggressively through silicone mats and into the chamber, and the next batch will taste of it. Either dedicate a set of mats to alliums, or run them last before a cleaning cycle. Freeze-dried strawberries that taste of garlic are a genuinely disappointing discovery.

What good looks like

A finished fruit slice snaps rather than bends, has no cool spot in the centre, and weighs the same after another two hours in the machine. Vegetables are the same test. If any piece flexes, the batch is not done.