Rehydrating freeze-dried food: ratios and soak times

Add roughly 80% of the water you removed, warm rather than boiling, and wait two to five minutes. Most foods come back faster than people expect. Dense cooked meals take longer, and it is always easier to add more water than to take it out.

The ratio

If you weighed the tray before and after — and this is the reason to do it — you know exactly how much water left. Add about 80% of that back. The remaining 20% accounts for water the food will pick up from steam, sauce or whatever you are cooking it into.

Food	Water to add	Time
Sliced fruit	Eat dry, or 50% for a compote	2–3 min
Peas, sweetcorn, beans	80% of removed weight	3–5 min
Cooked rice, pasta	80–90%	5–8 min
Cooked meals, stew	80%	5–10 min
Shredded cooked meat	70–80%	5–10 min
Raw meat	80%	10 min, then cook
Milk powder	As per original volume	1–2 min, whisk
Eggs	70%	2–3 min, then cook

Warm water, not boiling

Warm water rehydrates faster than cold without cooking the food while it rehydrates. Boiling water can turn the outside of a piece to mush before the middle has taken up any water at all, which gives you the same uneven result as drying too thick.

The exception is anything you are adding to a hot dish anyway — freeze-dried vegetables going into a simmering soup rehydrate in the soup and need no separate step.

Foods that do not need rehydrating

Plenty of freeze-dried food is better dry. Fruit, candy, cheese crisps and yoghurt drops are snacks in their own right, and the crisp texture is the point. Freeze-dried fruit in cereal or a smoothie rehydrates itself.

The safety exception

Raw meat must be cooked after rehydrating. Freeze drying is preservation, not sterilisation — whatever was on the meat when it went in is dormant, not dead, and comes back with the water. Rehydrate, then cook as you would fresh.

Common mistakes

• Too much water. The commonest one, and irreversible. Start at 70% and add.
• Not waiting. Dense pieces need the full five to ten minutes. Stirring early breaks them up before they have softened.
• Cold water on cooked meals. Works, but takes three times as long.
• Rehydrating more than you will eat. Once it has water in it, it is fresh food again with a fresh food shelf life.