How to Freeze Fruit Safely: −18 °C (0 °F), No More Than 1.5 kg per 30 Litres a Day, 8–12 Months of Quality

Frozen fruit is safe indefinitely but keeps its best quality for 8 to 12 months at −18 °C (0 °F). How much a freezer can take at once, three packing methods, the vitamin C dose against browning and thawing rules.

−18 °C (0 °F): safe indefinitely, tasty for 8 to 12 months

The FDA says a freezer should run at 0 °F, which is −18 °C, and states that food in the freezer stays safe indefinitely, only its flavour and texture change over time. The limit that applies to quality comes from the National Center for Home Food Preservation (NCHFP) at the University of Georgia: fruit and vegetables properly packaged and held at −18 °C (0 °F) or below keep their quality for 8 to 12 months; after that they are still safe, just poorer.

Freezing does not kill bacteria. The NCHFP warns that bacteria present on food before freezing start multiplying again as soon as the food thaws above 4 °C (40 °F). So only sound fruit goes in the freezer: the FDA recommends washing under running water, without soap, detergent or commercial produce washes, cutting away bruised parts, discarding rotten fruit and drying with a clean towel. The NCHFP adds that sugar is not a preservative, it only keeps colour, flavour and texture, so unsweetened fruit is just as safe.

Freezing speed decides the texture

Fruit that freezes slowly loses quality because large ice crystals form. The NCHFP therefore sets a limit: in 24 hours add only as much fresh food as will freeze in that time, which is 2 to 3 pounds per cubic foot of space, roughly 1 to 1.4 kg per 28 litres of freezer. For a 30-litre drawer that is one to one and a half kilograms of cherries or strawberries a day, not the whole crate. The day before a big freezing session turn the thermostat down to −23 °C (−10 °F), put packages against the cold walls in the coldest part and leave gaps between them until they are frozen; only then stack them tightly.

The same source recommends a tray: spread prepared fruit in a single layer, freeze, then immediately tip into a bag or container and return to the freezer. The pieces stay loose, you take as much as you need, and prompt packaging prevents freezer burn. Cool syrup and fruit before packing, because warm contents slow freezing.

Three packing methods and the vitamin C dose

The NCHFP distinguishes the syrup pack (for fruit eaten raw), the sugar pack (for pies) and the dry pack with nothing added. A 40 % syrup is made by dissolving 2 ¾ cups of sugar in 4 cups of lukewarm water, a 50 % syrup from 4 cups of sugar in 4 cups of water; the syrup must be cold. For fruit that browns, ascorbic acid is added: half a teaspoon (1,500 mg) per quart (about a litre) of syrup for apples and cherries, or the same amount in a cup of mashed banana. Containers must be moisture-vapour resistant, and headspace is left for expansion: ½ inch (1.3 cm) for a dry pack and 1 inch (2.5 cm) for a quart liquid pack with a wide opening. Label every package with the name, date and quantity.

Fruit	Preparation (NCHFP)	Pack
Bananas	ripe, firm; peel and mash	½ tsp ascorbic acid per cup of mash, sealed container
Apples	peel, cut into 12 slices	40 % syrup + ½ tsp ascorbic acid per quart, or steam-blanch 1.5–2 min, then tray
Cherries	dark varieties, wash, stem and pit	40 % syrup + ascorbic acid, or dry pack
Strawberries	ripe, deep red; wash, remove caps	50 % syrup, or ¾ cup sugar per quart of berries, or tray

What not to freeze raw

The NCHFP list of foods that do not freeze well starts with salad: lettuce, cucumbers, cabbage, celery, radishes and parsley go limp and waterlogged after thawing and quickly develop an oxidised flavour. All fruit can be frozen, but the texture suffers; the NCHFP therefore recommends serving frozen fruit for dessert while it still has a few ice crystals in it, because that masks the softness.

Thawing: never on the kitchen counter

Food is thawed in the refrigerator at 4 °C (40 °F) or below, under cold running water below 21 °C (70 °F) or in the microwave if it is used at once. At room temperature the outer layer enters the danger zone between 4 and 60 °C (40 and 140 °F) while the centre is still frozen. The NCHFP gives concrete figures for fruit: a 1-pound (450 g) package in syrup thaws in 6 to 8 hours in the fridge or ½ to 1 hour under cool running water, and sugared fruit thaws faster than unsweetened. According to the FDA, food that still has ice crystals or is at 40 °F (4 °C) or below may be refrozen. Leftover thawed fruit is best cooked, into compote or a filling; find ideas at jelo.hr/recepti.