Most vegetables dry better after two minutes in boiling water. Fruit, onions, peppers, mushrooms and tomatoes do not need it at all.
The short answer
Blanch beans, carrots, peas, corn, broccoli, cauliflower and potatoes. Skip blanching for onion, garlic, pepper, mushroom, tomato, courgette and all fruit.
Two minutes in boiling water, then straight into ice water, is enough for most cut vegetables. Cut them first, blanch after, and drain well before the trays go in.
Why hot water helps a dried carrot
Vegetables carry enzymes that keep working after harvest. Drying slows them down but does not stop them, which is why an unblanched carrot can taste flat and papery after a few months in the jar. Heat switches those enzymes off, a step food science calls enzyme inactivation.
There is a second effect that matters more day to day. Blanching softens cell walls, so water leaves faster during drying and comes back faster when you cook. Blanched green beans rehydrate in about half the time of unblanched ones.
How long for what
| Vegetable | Boiling water | Steam | Notes |
|---|---|---|---|
| Green beans | 2 min | 3 min | Cut to 25 mm first |
| Carrots, sliced | 2 min | 3 min | 5 mm slices dry evenly |
| Peas | 1.5 min | 3 min | Shell before blanching |
| Sweetcorn, cut | 2 min | 4 min | Blanch on the cob, then cut |
| Broccoli florets | 2 min | 3 min | Soak in brine first if you want to remove insects |
| Potatoes, sliced | 5 min | 6 min | Prevents grey discolouring |
Steam or water
Water blanching is faster and easier to time. Steam blanching takes roughly half again as long but holds on to more of the water soluble vitamins, so it suits leafy greens and peas.
Either way the stop matters as much as the start. Move the vegetables into ice water immediately, or they carry on cooking and turn to mush on the tray.
When skipping it is fine
If a batch is going into soup within a month or two, unblanched vegetables will taste fine. The difference shows up in long storage and in texture after rehydration, not in the first weeks.
Onions, peppers and mushrooms actually keep more flavour raw. Blanching them washes out the aromatics you dried them for.
Safety note. Blanching is a quality step, not a safety step. It does not make food safe to store at room temperature. Dryness and packaging do that.
What this is based on
- USDA Complete Guide to Home Canning and drying guidance
- National Center for Home Food Preservation, drying vegetables
- University extension publications on blanching times