Eat 'em before they get mouldy!
December 14, 2007 12:44 AM   Subscribe

Why do my banana muffins go so mouldy so quickly?

I was a short order cook while working my way through my Undergraduate degree, so since marrying Mrs Mutant I've taken on responsibility for cooking our meals. I particularly enjoy keeping the house full of cakes, breads and muffins.

However I've been frustrated by mould rapidly appearing on some of my muffins. Although this sometimes happens in as little as three days, its very inconsistent in terms of time, and I don't understand what's causing it.

I made several dozen carrot muffins (we juice a lot and muffins are a good use for the pulp) that never developed mould over the two plus weeks it took to consume them. Same thing for apple muffins over a one week horizon. Last Sunday, however, I made two dozen banana muffins, several of which developed mould in three days while in sealed a plastic container, which was never opened (there were plenty of other muffins to be eaten). Other batches of banana muffins moulded in less than a week.

Thinking it was perhaps the self raising flour, I've switched brands, twice now. The recipe I'm using is pretty basic (proportions & actions left out for brevity) :
  • Bananas
  • Honey (we avoid processed sugar)
  • Olive oil
  • Milk
  • Eggs
  • Butter
  • Self-raising flour
  • Salt
  • Cinnamon
  • Walnuts
I've tried a couple of brands of different self-raising flour with the same results. Perusing the labels I haven't noticed any preservatives listed. We live in London - is it possible the ingredients don't detail a sufficient level of granularity, and the flour does indeed contain preservatives?

Even so, I'm very puzzled why only my banana muffins mould. I can purchase three dozen ripe bananas for two pounds (after a little negotiating) at a London street market, so I'd like to continue to use this cheap fruit for muffins. But it's only my banana muffins that go bad so quickly.

Any suggestions?
posted by Mutant to Food & Drink (14 answers total)
Best answer: Mould likes available moisture. Try one of these things:
- cut back other liquids
- use raw sugar
- more salt
- less milk
- less banana
- baking for a little longer than usual
- make smaller muffins (more surface = less moist interior)

And don't let the bananas get too ripe. It's possible that the mould is already in the bananas, just not visible, and that the odd cell survives in the middle of a big muffin.
posted by i_am_joe's_spleen at 12:52 AM on December 14, 2007

Could you freeze them? They're particularly lovely rewarmed.
Not that that answers your specific question about why.
But it may solve the problem.
posted by taff at 1:23 AM on December 14, 2007

If there were preservatives in your flour, it should inhibit mold growth, not encourage it.
posted by happyturtle at 2:01 AM on December 14, 2007

The baking process should kill any mold/spores that are actually in the batter, so perhaps by way of peeling all your bananas you increased the number of mold spores in the air, which (perhaps) settled upon the cooling muffins, which then (perhaps) caused them to mold more quickly, even in a sealed container. If this is so, then you could peel the bananas elsewhere and cover your muffins with a cloth as they cool, and this might help. Woo hypothesis!
posted by beerbajay at 3:30 AM on December 14, 2007

Best answer: ...several of which developed mould in three days while in a sealed plastic container

Banana muffins are already high in all the things mold loves. Sealing them in an airtight container is like creating a Tupperware petri dish. Remember, it may be airtight, but it's not a vacuum in there. Air movement is actually preferred, in this case.

Place the muffins in a ventilated storage bag. One of those large zip-top baggies will be fine (take a sharp knife and poke some holes in the bag.) Add muffins. Store in the fridge. They should last a lot longer than 3 days.
posted by Thorzdad at 4:15 AM on December 14, 2007

Oh, and use something like a canola oil, instead of the olive oil in the muffins. Olive oil tend to go bad much faster than other baking oils.
posted by Thorzdad at 4:17 AM on December 14, 2007

I never make more banana bread than my family can eat in a day or two. I make all kinds of bread, and when I pick up a slice of banana bread, I'm always struck by how cool and moist it is, almost damp. It's just the nature of the banana, I think, since I use exactly the same ingredients (except for the bananas) for several other breads, and none of them are wet a day or so later when I pick them up.
posted by iconomy at 4:27 AM on December 14, 2007

I was also going to mention the olive oil. I know that other baked goods made with olive oil also go bad more quickly than those made without, so that might certainly be a factor.

As for storage, I've always kept banana breads under a tea towel or loose aluminum foil, something that lets the air through, and they've lasted over a week.
posted by bassjump at 5:30 AM on December 14, 2007

Three days is a long time for baked goods. Ever notice that bakeries have their goods marked down by half when they are "day old"? Eat them within a day or two or freeze them. Keeping moistly baked items in a plastic container is also a recipe for disaster. Just wrap them loosely in foil but again this won't keep them for long.
posted by JJ86 at 6:08 AM on December 14, 2007

Yes, banana muffins are mold heaven. Make small batches, or freeze part of a large batch and pull out portions to thaw when you want a couple of day's worth handy. Keep them well-aerated when they're stored out of the freezer.

Or freeze them all, and nuke/thaw each one as needed. Speaking from experience, frozen baked goods really help with impulse control. :-)
posted by maudlin at 6:56 AM on December 14, 2007

Like others, I'd say it's a combination of the moistness and the seal. I make a type of chocolate bran muffin that's very moist most of the time. If take them out of the tins I baked them in, turn them upside down and let air help dry them a little and keep flowing over them, they're fine for 3-4 days. If I leave them in the tins, the bottoms rot out by the next morning. If I take them out of the tins and throw them in a ziploc bag, they're okay, but only for 2-3 days. In the fridge, still only really okay for a week or so, but there, more because they eventually dry out and get skanky, and not because they start to mold like they do on the counter. Of course, if I take them out of the tins and throw them in a ziploc bag in the freezer, they're fine for 2-3 months before they get freezer burnt.
posted by jacquilynne at 7:25 AM on December 14, 2007

Yes, olive oil may go bad faster than other oils, but because it goes rancid (a purely chemical reaction, not requiring microorganisms), not because it is somehow more prone to mold or bacterial growth.

As others have said, it's the fact that these are moist fresh muffins, and you are sealing them up, insuring that the surface stays very moist.

Refrigerate or freeze them if you have more than you can eat in a day or two.
posted by Good Brain at 10:00 AM on December 14, 2007

I share the theory that it's basically that baked bananas are mold's favorite food. Of everything I bake banana-based quick breads are hands down the most mold susceptible - more so, it seems to me, than things like pumpkin bread that are similarly moist and which I store in exactly the same way.

You can freeze extra bananas, you know - They're pretty sloppy when they thaw so keep them in a plastic bag and handle carefully after thawing, but if you want to buy bananas in bulk and only use a few at a time, I've made fine bread out of bananas that have been in a bag in the freezer for up to a couple months.
posted by nanojath at 10:47 AM on December 14, 2007

I keep banana bread and muffins wrapped in foil or a tea towel. I've never had mold develop, but they are usually gone by day 5.
posted by oneirodynia at 12:43 PM on December 14, 2007

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