How to store onions and garlic, by the postharvest data

1. 01

   Dormancy is short; what follows is suppression

   Across three cultivars over three years, transcriptional differences were greater between harvest and pre-sprouting than between pre-sprouting and post-sprouting samples, with significant changes during the short curing period, which the authors read as the transition from endo-dormancy to sprout suppression and as evidence that endo-dormancy is a relatively short period ending just after curing (Chope et al. 2012). After that the storage environment, not the bulb, is doing the work.

2. 02

   The biochemical signature of a bulb about to sprout

   Principal component analysis of biochemical and physiological data identified the ratio of monosaccharides, fructose and glucose, to the disaccharide sucrose, along with the concentration of zeatin riboside, as the important factors discriminating sprouting from pre-sprouting bulbs (Chope et al. 2012). The bulb is remobilising stored carbohydrate before anything green appears, which is why a bulb that looks fine can be past the point of no return.

3. 03

   Curing hotter buys nothing

   Bulbs cured at 20, 24 and 28 degrees Celsius showed no detrimental effect on storage life or quality from curing at the lowest of the three, which the authors noted produces a considerable saving in energy and costs (Chope et al. 2012). For a buyer this is a supply-chain fact rather than an action, but it explains why sacks from different growers behave so differently in the same cupboard: much of the storage outcome was set before purchase.

4. 04

   Cool extends, but ambient can still reach seven months

   Four onion cultivars stored at 5 plus or minus 1 and 25 plus or minus 1 degrees Celsius at 60 to 70 plus or minus 5 percent relative humidity, with storage ending at loss of marketable quality or sprouting, showed that a genuine storage landrace kept at least 7 months at 25 degrees and could be held longer at 5 degrees without significant marketability or quality loss (Petropoulos et al. 2016). Cultivar is doing as much work here as temperature.

5. 05

   The humidity number is 60 to 70 percent, which is dry

   Both storage temperatures in that comparison were run at 60 to 70 plus or minus 5 percent relative humidity (Petropoulos et al. 2016). That is the opposite of the high-humidity conditions that suit leafy produce, and it is the single detail most domestic storage gets wrong. A sealed plastic bag traps respiration moisture against the tunic and invites rot; a paper sack, mesh bag or open basket in a dry cupboard is close to the tested condition.

6. 06

   At ambient, the loss is water rather than rot

   Over 144 days of ambient storage, no rotting appeared up to 24 days and no sprouting up to 84 days, while physiological loss in weight ranged from 28.5 to 63.6 percent across treatments at five months, and ascorbic acid decreased significantly throughout (Sharma et al. 2020). An onion that has gone soft in a warm kitchen after three months has dehydrated on the scale of a third to two-thirds of its mass rather than spoiled.

7. 07

   Garlic loses allicin at fridge temperature

   Peeled garlic cloves in modified atmosphere packaging held at 0 and 5 degrees Celsius for four months lost firmness and vitamin C notably, showed higher weight loss and titratable acidity at 5 degrees than at 0, and allicin content generally decreased at 5 degrees, with the conclusion that cloves keep up to four months at 0 degrees or three months at 5 (Akan et al. 2019). Domestic refrigerators sit in that warmer, worse band.

8. 08

   The decision rule, in one line each

   Whole cured bulbs: cool, dark, dry at roughly 60 to 70 percent relative humidity, in a container that breathes rather than seals (Petropoulos et al. 2016). Not the refrigerator, which is both too humid for the papery skins and, for garlic, warm enough to cost allicin (Akan et al. 2019). Buy in quantities that will be used, because the storage ceiling was largely set by growing and curing (Chope et al. 2012). Treat sprouting as the end of the window and softness as water loss.

What people ask us next.

Q01

Should onions be kept in the refrigerator?

Whole cured onions should not. The tested storage condition for onion bulbs was 60 to 70 plus or minus 5 percent relative humidity at either 5 or 25 degrees Celsius (Petropoulos et al. 2016), and a domestic fridge is considerably more humid than that, which traps moisture against the papery tunic and invites surface rot. A cool, dark, dry cupboard with air movement matches the tested condition better. A cut onion is a different case and belongs covered in the fridge.

Q02

Why does garlic go rubbery or lose its bite in the fridge?

Because both its texture and its active chemistry move at those temperatures. Cloves held at 0 and 5 degrees Celsius for four months lost firmness and vitamin C notably, with higher weight loss and titratable acidity at 5 degrees than at 0, and allicin content generally decreased at 5 degrees over the period (Akan et al. 2019). A domestic refrigerator runs near or above 5 degrees, so it is in the worse half of that comparison while also being too humid for the skins.

Q03

How long should onions keep at home?

Longer than most people assume, and the ceiling is set by the cultivar and the curing rather than by the cupboard. A genuine storage landrace kept at least 7 months at 25 plus or minus 1 degrees Celsius at 60 to 70 percent relative humidity, and could be held longer at 5 degrees without significant quality loss (Petropoulos et al. 2016). A sweet or fresh-market onion will not do that, which is why the same storage conditions produce very different results with different sacks.

Q04

Is a sprouted onion or garlic clove safe to eat?

Sprouting is the end of the storage window rather than a safety event. It marks the release of sprout suppression, and the bulb has already begun remobilising stored carbohydrate, with the monosaccharide-to-sucrose ratio and zeatin riboside concentration discriminating sprouting from pre-sprouting bulbs before anything is visible (Chope et al. 2012). The texture softens and the flavour changes as the bulb feeds the shoot. Trim and use, or discard on quality grounds.

Q05

Should onions and potatoes be stored together?

No, and the reasons are separate for each. Onions want dry air at around 60 to 70 percent relative humidity (Petropoulos et al. 2016), while potatoes are the one produce item with a specific chemical reason to be kept cool but not cold, since cold storage raises reducing sugars that generate acrylamide on high-temperature cooking, a case covered in the vegetable storage analysis on this site. Storing them together forces one compromise on humidity and another on temperature.

Q06

Does a soft onion mean it has gone bad?

Usually it means it has dried out. Across 144 days of ambient storage, physiological loss in weight reached 28.5 to 63.6 percent at five months while no rotting was observed up to 24 days and no sprouting up to 84 days (Sharma et al. 2020). Softness on that scale of water loss is a quality problem, not a spoilage one. Visible mould, a wet or slimy layer under the skin, or an off smell is a different signal and a reason to discard.