Why they harden or sugar
Dry grapes are held between two problems. Too much moisture lets mould grow. Too little air moisture makes them hard.
Sugaring is the formation of crystals on or inside the fruit, from the natural sugars and acids in grapes. It happens after drying.
A study cited by a raisin-industry report found that raisins at 10 to 12 per cent moisture showed little sugaring after a year. At 14, 16 and 18 per cent moisture, crystals covered about 11, 28 and 36 per cent of the surface. Swings in storage temperature and humidity also add to it.
White crystals are not mould. They are harmless, though the texture can become gritty.
Store them well
- Use an airtight glass jar with a gasket lid. Glass does not pick up or pass on flavours.
- Press out air if using a bag. Vacuum-sealed bags suit bulk storage.
- Keep the jar in a cool, dark cupboard, away from the stove and sunlight.
- Keep spoons dry. A wet spoon puts moisture in.
- Always close the lid after use. Humid air is the main enemy.
Dry-fruit textbooks put ideal storage humidity near 50 per cent. In the monsoon months, a jar with a good seal matters even more.
How long do they last
One source says room-temperature storage in a cool, dark place suits one to two months of regular use. In the fridge it extends to about six months to a year, since cold slows sugar crystallising. Frozen and sealed, it can run beyond a year.
Sealed bulk raisins stay stable for several months at room temperature if kept from insects. Always follow the best before date on your pack.
Keep pests out
Insects can chew through thin packaging. Move dry grapes into an airtight container. Some advice is to freeze new stock for 48 hours before keeping it in the cupboard, to kill any eggs or larvae.
Reviving hard dry grapes
- Cover with boiling water for 10 to 15 minutes, then drain.
- Or microwave with a little water for 30 to 60 seconds.
- For gradual conditioning, cover with lukewarm water, drain at once, and leave covered for several hours. Fruit gains about 10 per cent moisture this way.
Revived fruit spoils faster, so use it within a few days.
How to soak for cooking
For baking, cover the fruit with hot water for 10 to 15 minutes and drain. Cold soaking in room-temperature water takes about 30 minutes.
Do not soak longer than needed. The fruit only plumps so much. Water is usual, and juice is another option. Do not leave soaked fruit out for long.
Buy small, open small
If you buy a large pack, split it. Keep a small jar for daily use and leave the rest sealed. Every time a jar is opened, damp air gets in, and a small jar is opened often while the sealed stock stays dry.
Label each jar with the date you opened it. Use the oldest first.
When to throw them away
Discard dry grapes that smell sour or fermented, or that show fuzzy mould. Do not confuse this with sugar crystals, which are dry and gritty.
Frequently asked questions
Are white spots on dry grapes mould?
Usually not. White crystals are natural sugar. Fuzzy growth or a sour smell is a sign of spoilage.
Should I keep dry grapes in the fridge?
It can extend freshness and slows sugaring. Use an airtight container so they do not pick up smells or moisture.
Can I soak dry grapes overnight and store them?
Soaked fruit spoils faster. Keep it covered in the fridge and use it within a few days.