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I'm having a problem where the blackberries I buy from the store on Sunday seem to be spoiled on Monday. On Sunday, I specifically look around the outside of the box and check if any blackberries have white fluff on them. If I don't see it then, then when I actually open the berries on Monday I will see the fluff. This is irritating because I don't know whether I am supposed to throw these out, and I buy large quantities of these berries to last me the week.

So my 2 questions are:

  1. How do I know whether a blackberry is safe to eat? If some blackberries have that white mold on it, but the others don't, can I throw that berry out and use adjacent berries?

  2. How am I supposed to store blackberries to prevent it from molding after 1 day? I highly doubt my grocery store will be selling moldy berries deliberately so maybe I am storing it incorrectly.

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    How are you storing them?
    – J Crosby
    Jul 8, 2019 at 15:15
  • I just put them straight in the fridge in the same box they came in. When I need to use them I just pull them out and use the amount I need and return it to the fridge. It's very strange since this problem started only in the last 2 months. I don't know if the grocery store is continuously selling moldy berries or not.
    – Jeremy Fisher
    Jul 8, 2019 at 16:36
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    You might have mold lurking elsewhere in your 'fridge. If so, a good cleaning, ending with a spray/wipe-down of all interior surfaces with 3% Hydrogen Peroxide may help.
    – Catalyst
    Jul 9, 2019 at 12:26
  • If this started in the past 2 months it might be your fridge temp has risen in summer? Are you monitoring high and lows?
    – user76453
    Jul 10, 2019 at 7:11

3 Answers 3

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As soon as you get them home, inspect for damaged berries & discard any that are not perfect. Wash the rest in a colander or sieve under cold running water. Drain well.

Spread on dry paper towel for 30 mins to fully drain & dry, then put them in a new box with paper towel under & over - don't seal them with a snap lid.

Place in the fridge, in the salad crisper if you have one.

Life-span should now be more like a week.

The rapid spread of mould is from possibly just one single damaged berry. If they are touching & sweating, that can spread like wildfire. If they are clean, dry & cold, in air that can circulate around them, then you should be fine.
You could possibly be OK eating ones from the opposite side of the original punnet, but I wouldn't really. Safe rather than sorry, so do the preventative work first.

If it happens again even after you took proper care, pick a new store, or complain at the first one - though bear in mind that even with care, they are still fragile & won't last forever. Your sign of end-of-life when clean & dry should be shrinkage, they will eventually start to dry out & look wrinkled, rather than mould.

From comments under the OP [1] - it's possible that the mould spores are in the fridge not in the berries. The berries, if damaged in any way, simply provide a suitable breeding ground.
I'd recommend a fridge-sanitisation day. My method will prevent fast cross-contamination, but won't kill existing spores.

[1] "It's very strange since this problem started only in the last 2 months. I don't know if the grocery store is continuously selling moldy berries or not"

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    Rough handling seems to be a significant factor, maybe before you buy them.
    – Chris H
    Jul 8, 2019 at 16:37
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    I got it now. Just basically a tupperware container with paper towel under and over the berries, without sealing the container.
    – Jeremy Fisher
    Jul 8, 2019 at 16:42
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    Jeremy - from your comment under the original question, I added a new part to the answer.
    – Tetsujin
    Jul 8, 2019 at 17:02
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    Lysol is toxic and meant to go on floors, not anywhere near food. Especially not in a fridge where it won't ever evaporate properly.
    – user57361
    Jul 8, 2019 at 23:34
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    Alcohol is a good antiseptic, which means it kills bacteria. Mold spores are.. mold. So alcohol is useless for that. Really the best way to kill mold spores without toxic outgassing or risking poisoning yourself is a borax solution. But that's not easily available in every country
    – user57361
    Jul 9, 2019 at 19:33
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How am I supposed to store blackberries to prevent it from molding after 1 day?

Buy frozen.

  1. They're fresher (picked ripe and flash frozen, versus picked unripe so they last to the grocery store).
  2. You can defrost only the ones you need.
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    If you only want them for making a couli or some kind of cooked pudding, frozen is fine. If you want them for a cold pudding like a pavlova, or to eat, freezing destroys the structure of the fruit. When you thaw it, it becomes mush.
    – Graham
    Jul 9, 2019 at 7:36
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    @Graham The whole point of flash freezeing ("vapour freezing" etc.) is that this doesn't happen. This is not the same as putting the fruit in your freezer. Of course, you need to make sure the fruit didn't at any point refreeze (often a problem in supermarkets).
    – Luaan
    Jul 9, 2019 at 8:09
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    @Luaan The point is that you can't stop it happening. Water expands as it freezes, and that's simply physics. For anything which is basically firm or fibrous, this isn't a problem - pineapple freezes really well, for example. But frozen soft fruit like strawberries, raspberries or blackberries are basically bubbles of fruity water, and that delicate structure is always broken down by freezing, whatever freezing technique you use.
    – Graham
    Jul 9, 2019 at 11:16
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    @Luaan ... Using "supermarket varieties" of soft fruit like Elsanta, which are chosen to be firmer but inevitably don't taste of very much, you get a less bad result. Raspberries can be less visibly affected, because they have a firmer skin. Either way though, the texture when you eat them is clearly not the same as fresh fruit. I don't disagree that there's a place for frozen soft fruit, but anyone who's eaten fresh fruit should recognise the texture difference between thawed-out soft fruit and fresh.
    – Graham
    Jul 9, 2019 at 11:20
  • @Graham the faster the freeze, the smaller the crystals (thus minimizing the damage). That's the whole purpose of flash freezing.
    – RonJohn
    Nov 29, 2019 at 22:25
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I wouldn't even try to squeeze a week out of blackberries. Basically they should be eaten the instant you get a hold of them, they're too fragile and not meant for storage. Tetsujin's answer would prolong their life by a few days, but not indefinitely. And any blackberries that lasted much longer would be so impregnated with preservatives that you should probably steer clear of them.

That said it's not at all unusual for a basket of soft berries, whether from the store or a market, to contain one or more that didn't even make it to you. I throw out any that are really moldy, eat the rest without ever having any sort of problem.

Don't use Lysol in your fridge, that's worse than any spores. Just clean it out well using baking soda as a scouring powder, making sure to clean any crannies, that for instance you pull out the drawers to clean under them. Or if you really have a raging mold problem, rinse it down with a borax solution, if you can get your hands on some (7-mule team brand in the US is usually sold with laundry).

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    Using any kind of abrasive on the plastic walls of a fridge also sounds like a bad idea.
    – David Richerby
    Jul 9, 2019 at 8:40
  • The only mention of Lysol in cooking SE is this post. Why is it bad?
    – J. Chris Compton
    Jul 9, 2019 at 18:18
  • Baking soda is a mild enough abrasive to use on your teeth, so it's fine for your fridge too. As to Lysol, it's meant to wash floors, it's not a food-grade product by any means.
    – user57361
    Jul 9, 2019 at 19:31
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    @GeorgeM Lysol is a brand name, not a product, and the brand includes a food surface sanitizer. Just because the floor cleaning product you're used to is not food grade does not mean no product they make is food grade.
    – Beofett
    Jul 10, 2019 at 19:45

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