February 16, 2009

Cold Storage of Onions

Posted in food storage tagged , at 5:43 pm by yjohn

First let me say that I love onions. Whether I’m making a rich bean stew or homemade ketchup, onions are the single indispensable ingredient that is required across the board. So it should be no surprise that I grow quite a few onions every year and store them for my culinary use.

It’s just about time for me to start the seeds indoors for my next batch of onions, which I’ll be planting out in April. In considering this, I thought some tips regarding proper cold storage of onions might be in order.

Don’t harvest onions prematurely. Onions are ready when the leaves have turned yellow and fallen over, but not before.

Choose a nice sunny day to harvest, and pull up the onions in the morning. Lay them out on a flat dry board in the sun for the day. Choose a light-colored board, incidentally. I use one that I painted white. If you use a dark-colored board, it will absorb too much heat and cook your onions!

Once the onions have cured in the sun, cut off the tops and store in a mesh bag (for good air circulation) in an area with minimal light, temperatures below 60 degrees and low humidity.

One thing you want to avoid is storing onions in a place where they might be exposed to freezing temperatures.

What not to do when storing onions

What not to do when storing onions

As you can see from the picture, the bag of onions on the left has sprouted whereas the bag of onions on the right is intact. What is the difference? The bag on the left was exposed to below-freezing temperatures in the garage for about a week whereas the bag on the right was not.

These “bags” incidentally are made from the legs of my wife’s old (but thoroughly cleaned) pantyhose. They give the onions excellent support without any spots of high pressure (that could cause them to go bad) while allowing plentiful air circulation. I can’t speak as to whether pantyhose makes sense as an article of clothing — I’d rather leave that determination to the people who actually use the product. But as bags for storing onions, they are peerless and inexpensive.

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3 Comments »

  1. Yogesh Dahiya said,

    Dear Sir,
    We are going to built onion cold storage in box palete of 2300 MT. We need your valuable suggestions as
    this the first project in India.
    We will be highly oblidge if you provide suggestions.
    Regards.
    Yogesh Dahiya
    Director
    Jaimin Engineering Pvt. Ltd;
    Gujarat.
    India.
    cell no: +9199099 56804
    ———————–
    John Young responds:

    This is a bit outside the scope of our focus on self-sufficiency; but we’re generally aware of the current and looming food problems that India is facing; particularly the issues pertaining to ground water shortages, and believe helping you with these is a good idea..

    You want to regulate the temperature effectively at about 1 degree Celsius. Use air circulation to make sure there aren’t cold/hot spots because once an onion freezes its storage properties are diminished. You will want to regulate humidity at about 50%.

    The specific cultivar of onion makes a big difference in cold storage suitability. You will want a medium-sized pungent onion. In this country, good choices would be Norstar and Copra. I’m not familiar with your growing climate, so you’ll need to choose a suitable variety for your area — just remember to avoid so-called “sweet” onion varieties as they store poorly.

    Likewise, the treatment of the onion after harvest is crucial to successful storage. Again, I am unfamiliar with your climate; but some general rules should be applicable no matter where you are:

    1. Stop watering about a month before harvest
    2. Harvest after the tops have turned yellow and fallen over of their own accord.
    3. Cure the onion in the sun until the tops and skins are thoroughly dry. Then, remove the tops but NOT the skin of the onion.

    Onions are best stored in mesh bags holding no more than 2kg of onions each. The mesh bags allow for air circulation while preventing putting too much pressure on any one part of the onion which could injure the cell structure and promote rot.

    If you will be storing 2500 metric tons of onions in this fashion, you will need to devise an ingenious powered hook system to hold the bags closely while still allowing them to be rotated for use.

    Another alternative is to store them in a single layer in padded drawers.

    Hopefully, you find this helpful!

  2. onkar singh said,

    dear sir
    i want to know that how we can store the onion for six to eight month &what the atmospheric condition required for storing of onion .Can we store the onion at normal temperature

    Thanks &best regards

    onkar singh

    ——————-
    Response:
    Onions should be stored at slightly above 32F (do NOT let them freeze), with relative humidity in the 50%-70% range.

    The TYPE of onion you choose is important! Sweet onions of the Vidalia type do not typically store well. Try something more pungent.

    Also, they should be harvested properly.

    Hopefully this helps!

  3. LuAnne said,

    2 years later, I wish to thank you for your article on storing onions. I try to grow some storage-type onions every year and find that just placing them in plastic buckets in a dry pantry, which is cool, but certainly not below 60 degrees, seems to work for me.


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