Why should we not store onions and potatoes together?

Question

I have heard that onions and potatoes shouldn't be stored together. Why will this make the potatoes spoil faster?

Asked by Dharini Chandrasekaran

Answer

As you can see at the Chapter 7: Storage of horticultural crops of the book PDF: Small-Scale Postharvest Handling Practices: A Manual for Horticultural Crops (4th Edition):

• If you look p.166 (p.173 on the PDF), you can see that the onions need to be stored in this conditions:
  • between 0-5°C with a relative humidity (R.H.) of 65-70%
• If you look p.168 (p.175 on the PDF), you can see that the potatoes have different needs:
  • Fresh market: between 4-7°C
  • Processing: between 8-12°C
  • seed potatoes: between 0-2°C
  • But must of all, potatoes need very highest relative humidity (R.H.): 95-98% versus 65-70% for onions

So, if you store them together, either one or the other will be in bad storage conditions.

Further, as you can see at Section 7: Storage of horticultural crops of Small-scale postharvest handling practices - A manual for horticultural crops - 3rd edition:

• Dry onions (Group 3) are very sensitive to moisture, which makes their storage incompatible with the high R.H. needed for potatoes.
• New potatoes (Group 6) may also produce ethylene, which will badly damage green onions (Group 2) if stored together.

Anyway, storage of horticultural crops cannot just be resumed by "don't put this or that together", as you may have seen:
it is important to consider R.H., temperature, and many other factors.

If the subject interests you, all this (and many other things) is pretty well explained in the following references:

• PDF: Small-Scale Postharvest Handling Practices: A Manual for Horticultural Crops (4th Edition)
• Web: Small-Scale Postharvest Handling Practices: A Manual for Horticultural Crops (4th Edition)
• WEB: Small-scale postharvest handling practices - A manual for horticultural crops - 3rd edition

Ethylene is also a "critical factor", and this topic is more developped in the following resources:

• PDF: Postharvest Ethylene: A critical factor in quality management.
• Book: Postharvest Technology of Horticultural Crops (see Ethylene in Postharvest Technology pp.149-162)

Answered by Pascal Qyy

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Can you store oil in a container that is not airtight?

Question

I've have seen that several chefs and home cooks (e.g. my mom) store oils like canola and olive in ceramic or glass bottles with pour spouts that are not sealed. An example of this can be found on Serious Eats

My girlfriend asserted that oils should only be stored in air tight containers as leaving them open to the air (even through a small pour spot opening) leads to oxygen getting into the container and affecting the oil.

Is it true that (1) oxygen can affect the quality of the oil, and that (2) an airtight container can prevent this in a noticeable way relative to the storage mentioned above? If it is, are most of the people using non-airtight containers going through their oil so quickly that it doesn't matter?

Answer

Yes, oxygen (and sunlight) can affect the quality of oil. The oil turns rancid after some time. And storing the oil in a really airtight container (like a can from which air has been evacuated before sealing) should prevent or at least slow the process.

However, the problem is that you can't practically store your oil in an airless container and still use it. Yes, you can seal a bottle of oil. But there will still be air between the oil surface and the stopper, and the oxygen from this air will react with the oil molecules on the surface. And if you use a non-sealed bottle, the exactly same thing will happen. Unlike other cases (soda in a sealed vs. open bottle), the reaction of oil and oxygen isn't quick and aggressive enough to quickly exhaust the small amount of oxygen in a sealed bottle and stop. It will go on regardless of whether there is free air flow from the atmosphere or not.

So what can you do? You can still minimize the rate of rancidification. But it isn't the openness of the bottle that matters, it is the contact area size, because this is where the reaction takes place. Which means, store your oil in a (preferably tall and slim) bottle, as opposed to something like a jug. Protect it from light, because light is definitely damaging for oil. Also, buy it in small sizes, so you can go through it in a reasonably short time. And after all, don't worry too much about it. The reactions are slow, and the oils you use several times per week will not last long enough in your kitchen to deteriorate too much. It can become a problem if you collect special oils which are used seldom and contribute a significant part of the taste in a dish.

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Why does fresh coriander deteriorate so quickly?

Question

I realize that, as I live in a northerly climate, I cannot expect to have fresh herbs like coriander always available at my beck and call.

Yet, yesterday I bought a lovely, thick bunch of coriander at the cheapo-supermarket closest to my home and it was fantastic: profuse, aromatic, and fully tumescent.

Now, 24 hours later, even though I refrigerated it in an vase with water (it has the roots still attached) it is looking like sh*t.

I know that greens deteriorate over time but the turn around time in this case seems ridiculous to me. Italian parsley, AFAIK, is also imported yet it lasts for weeks in the crisper.

Is the only reason coriander looks good on the shelf is that it is spritzed every 90 seconds?

Answer

Theory 1: moisture

Were the leaves wet at all? I worked in a restaurant before, tending to the fridge. I had to make sure the salads were washed and thoroughly spun. Wet greens wilted and rotted faster and we had to toss them. The roots can be wet and exposed to water, but make sure the leaves stay dry.

Theory 2: freezer burn

This link mentions that cilantro can be damaged by freezing temperatures, which could be an explanation for what you're seeing? Is it so cold in your area that your refrigerator actually dips into freezing temps because the air around it does?

Meats can get freezer burn or taste off after freezing. One explanation I've read is that water freezes as sharp crystals in and around the cells. Upon defrosting, these sharp crystals can cut through cell membranes, causing cell contents to leak out and alter the meat structure. In theory the same could apply to anything organic.

Theory 3: dehydration

The link above and others I've read suggest storing cilantro as you do in the fridge, but covered with a plastic bag. Some wrap their cilantro in a paper towel. Either way, this creates an enclosed or somewhat-enclosed space that slows down moisture escaping from the leaves. The air in the fridge is generally dry and can suck moisture out of the leaves. I know this sounds like the opposite of too much moisture, but there's a window for how much moisture plants want--neither too little nor too much is desired.

I'd try to resolve this in the order above. If you left the leaves wet, I'd say that's a very likely culprit. I'd check your fridge temperature next: you could put an ice tray near where you put the cilantro to see if it freezes or starts freezing overnight. If it's still wilting fast, try doing what you did with a plastic or paper bag over the leaves--making sure the bag isn't crushing them.

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Storing cut button mushrooms vs whole button mushrooms

Question

Do cut buttons mushrooms have a tendency to spoil more quickly than whole button mushrooms?

Also, what are signs that a button mushroom has gone bad ?

Just curious about this.

Answer

Anything will spoil more quickly if cut than if whole. It's all a matter of surface area.

The bacteria/fungi/mold/whatever can only attack the surface that is open to the air. When you cut the mushrooms, you open more surface up to attack, and hence they will be affected more quickly. This is equally true for dehydration and loss of flavour (by evaporation), which are also linked to surface area.

With regards to spoiled mushrooms, a quick sinff will usually give away any dodgy mushrooms. They tend to stink like nobody's business when they've gone south. If they look right and smell right, they're most probably fine.

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