Curing Onions for Storage

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Torpedo onions

Of all the articles I have written here, the one with the longest list of comments is The Art of Harvesting Onions, which appeared three years ago this week. More than 80 of you have contributed thoughts and ideas on the subject, so clearly there is much to discuss.

Picking up where I left off, this time around I will focus on the fine points of how to cure onions, which you will need to do if you expect your onions to store well. Fresh from the garden, onions are full of sugary juices, and they wear only a light covering of skin. As onions cure, the skins dry into papery wrappers, pungent compounds replace sugars, and the necks at the top of the bulb come together to seal out moisture and microorganisms.

Of course, not all onions need to be cured. Gardeners in warm climates who grow mostly short-day onions need only dry the harvested onions for a few days before trimming them and moving them to the refrigerator. I do the same with some of my heirloom onions, most notably my red Italian torpedo onions, which don’t store worth a flip even when perfectly cured. Instead of going to the trouble of curing sweet onions like these, I think it’s best to let them dry in warm shade for less than a week, and then put them in the fridge and start eating them.

Harvested onions

How to Cure Onions

As for full-season onions with good storage potential, commercial onions are typically cured at very warm temperatures for six weeks, and then gradually cooled down to refrigerator temperatures. However, recent research indicates that curing onions naturally, by keeping them in a warm, dry place for a month, will work just as well. Thinking it might save energy, a team of UK researchers set onions to cure at various temperatures, and found that 68°F (20°C ) worked almost as well as 82°F (28°C), the standard recommended temperature for this process.

This does not surprise me, but it barely touches the surface of how to cure onions at home. In my experience, newly pulled onions benefit from being dried immediately, but not in direct sun, which can cause uneven drying. After trimming off shriveled leaves and tickling clods of soil from the roots, I lay my newly pulled onions in a single layer in a covered shed, where temperatures range between 60°F (15°C) at night and 80°F (27°C) during the day. There they rest for about a week, and I try not to touch them. Uncured onions bruise easily, so it’s important to handle them like eggs.

Opinions differ on whether it is best to lop off most of the green onion leaves or leave them intact. Recent research from Sweden indicates that the onions don’t really care. Once the necks have thinned to the point of breaking, the bulbs are no longer receiving nutrition from the leaves. If you want to let your onions finish curing in a braid, trim off all but the three newest leaves, and use the remainder for weaving, or for tying together small bunches of onions.

Onion braid

I like to top back onions gradually, leaving a longish stub of stem that will help protect the neck of the onion as it slowly shrinks until the opening is closed and the onion within is protected. During the four to six week curing period, I usually trim back the tops two or three times, but wait until the curing onions are ready to be brought indoors before clipping the necks off altogether.

Commercially-grown onions have their roots clipped off at harvest, but I like to let them dry naturally for a week or so, and then use scissors to trim the roots back to one-fourth inch (6mm). This small bit of patience gives the onion’s basal plate time to dry, signaling the onion to enter a state of deep dormancy.

How to Store Onions

Onion varieties vary in their natural dormancy periods. Some are ready to start regrowing after two or three months, while others will keep for six months or more in a cool, dry place. Refrigeration will keep short-dormancy onions quiet longer, but it’s still best to eat them fresh and save your storage efforts for bulb onions and long-storing shallots.

Cured onions

After a month or more of curing outdoors, you are ready to sort through your collection and select the most perfect onions for storage. At this point I take out obvious doubles, in which two bulbs are joined together, because doubles often develop a soft spot in the middle that lead to spoilage. I also set aside onions with split scales, because split wrapper scales cannot protect the onions from moisture loss or invasion by fungi and bacteria. I use these imperfect onions in canning and freezing, or we eat them fresh.

As for the keepers, they are allowed to cure one last time indoors, where it is consistently cool and they go deeper into dormancy, getting ready for winter. By the time winter actually comes, the basement is cool enough for long-term storage.

Sometimes I put onions in mesh bags for hanging, but more often they go into small baskets no more than three onions deep. In addition to allowing some air circulation, the shelves or containers you use for storing onions should be easy to check, because good onions can go bad unexpectedly. Each time I bring up onions from the basement, I take a minute to sniff around for signs of trouble. When a stored onion goes bad, you will smell it long before you see it.

By Barbara Pleasant

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Comments

 
"Thank you for your timely article. Here in very humid CT I have some shallots drying on a table with newspapers. In an effort to decrease the humidity in the room (dewpoints have been running 70%)I have been running a dehumidifyer to dry out the room. Will do this with the rest of the onion crop as it comes in."
Jenn on Friday 19 July 2013
"Great info! It's been hot and very humid (as usual in the summer) here in Raleigh, NC. I pulled my crop and set them on cardboard in my shop building and have had a fan blowing on them for about 2 weeks. They seem to be curing very well. I have some concerns about the heat and humidity but hopefully, the fan helps."
Jake on Friday 19 July 2013
"Thanks for sharing your experience. We are also having a VERY humid July in Rhode Island. We are currently trying to cure garlic and three varieties of onions. About 1/3 of our garlic rotted in our extremely wet June. Fortunately, less than 10% of the onions failed in June. "
Sanne on Friday 19 July 2013
"I've been storing my onions forever in West Texas. I put them in old panty hose and hang them up in a barn. Our temps are much warmer than this article and we rarely drop below 72 in the summer and can get as hot as 112. They will stay in my barn hanging up until March or April"
David in West Texas on Friday 19 July 2013
"David in West Texas- really??? your onions are curing from now (July) until March or April??? Have you used some along the way- how are they when not totally 'cured'? I had red onions - really great- pulled from the ground, here in southern California- without curing and they were just delicious. Still learning about curing my garlic. Growing season here is all year but tricky!"
Eileen on Saturday 20 July 2013
"We had a really late freeze so I haven't harvested all of my onions yet. Just those I need to use but they do last all winter in the barn and we do have temps into the teens then. Imalways surprised how well they last but my familia has done this for 40 years. My family are very large cotton farmers so we have huge gardens. "
David in West Texas on Sunday 21 July 2013
"I'm from Papua News Guinea in Simbu province. We are growing bulb onions bulb having problem curing. We're in the highlands. Any help in curing would help."
Morris Kaupa on Tuesday 3 March 2015
"I'm currently curing some Walla Walla sweet onions in the garage but we are in the middle of a heat wave and it gets up to 110 degrees in there. I haven't put a fan on them. I'm worried it's too hot and will ruin or something. Maybe the process will just go fast...Not sure...any insight? I don't have any where else to put them only air conditioned house. "
Pam on Saturday 11 July 2015
"Thanks for your great article. Great. A picky little comment about trimming the roots.. 1/4 inch would be 6mm vs 6 cm."
TJ on Friday 24 July 2015
"Thanks for your eagle eyes TJ - we've fixed that now."
Ann Marie Hendry on Saturday 25 July 2015

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