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A little while ago we froze a packet of those pancake-like products that in these parts we call crumpets. At the time, the sealed plastic packet seemed to contain a lot of air, but after four months in our freezer it had contracted tightly against the crumpets, which had also shrunk. After two more months at room temperature, the whole package appeared to have shrunk still further, though with no sign of mould or decay (see photo, left).The ingredients are listed as flour, water, yeast, raising agents, E450, E500, salt, sugar, preservative, calcium propionate. What's going on?Chris Greenwood, Ettington, Warwickshire, UK

Editorial status: In magazine.

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Answered by Sabrina.
on 2008-11-30 17:40:00

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Hey.I'm not an expert either, so I don't know why the air would've collasped ... but I think that reason that no mould grew etc. was because there was no air. If the pack was tightly sealed like you said then no air would've been able to get in ... so no oxygen and hence - no life.=]Sabrina.

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Asked by Michael Marshall
on 2009-07-01 17:28:59

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Categories: Domestic Science, Technology.

Tags: human body, unanswered, domestic science, technology.

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Thinking person's crumpet

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Answered by Anonymous
on 2008-12-01 22:36:00

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Yeasts break sugars down to water and carbon dioxide,consuming oxygen and in the process making some unintended hydrogenperoxide, which must be removed using catalase. The hydrogen peroxide is broken down bythe catalase in yeast, in this reaction: 2 HOOH --gt; 2 H2O + O2I#39;m no chemist but I believe all this rearrangement of the molecules by the yeast causes the pressure from the gases in the package to be less than what it was when the product was first packaged. Hence a partial vacuum develops in the package and it appears vacuum-packed.

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Asked by Michael Marshall
on 2009-07-01 17:28:59

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Categories: Domestic Science, Technology.

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Thinking person's crumpet

Editorial status: In magazine.

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Answered by Anonymous
on 2008-12-02 21:25:00

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PV=nRT

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Asked by Michael Marshall
on 2009-07-01 17:28:59

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Thinking person's crumpet

Editorial status: In magazine.

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Answered by Martin
on 2008-12-03 08:15:00

(1 vote) average rating:4

Hmmm a really interesting one, as this is unlike anything I have seen if my Food Science classes at Universiteit Stellenbosch....While the yeast reactivity is one plausible hypothesis (it certainly sounds good on the surface), there's no way to prove it short of opening the package and seeing if there is whiff of alcohol to go with it. And three of the components namely E500 aka Sodium Bicarb indicate that there's can't be very much yeast in there, as the bicarb was needed to raise the crumpets. Also, this means the yeast is dead - they are baked before being placed in the package, and it would literally take 6 months for them to grow, and most yeasts, particularly the classic Saccharomyces sensu stricto used in baking tends not enjoy being cold. So that rules that one out.No, in this case - I would give my professional opinion that there is a chemical, rather than biochemical reaction going on in there, and the most likely culprits are a possible interaction between the cations of Sodium Bicarb (E500), Calcium Propionate (E430), and Salt...and I suspect also there was a little bit too much water in the mix, allowing a fair degree of mixing. The subtraction of gas due to cooling is likely also to be a gas-density effect, made worse by chemical generation of a small amount of peroxide radicals. Some physical interaction is also experienced by the film coating the crumpets - I have also had lots of food using Saran/Polyethylene wrapping (like your crumpets have got) also going through a shrink, and they definitely did not have any yeast or peroxides in them. Polyethylene, in thin films is farily tempt sensitive in the low end (this from my Food Machine Engineering course, those steam tables were hard!), and shrinks quite a lot....Thats my very best guess - a bit of microbial fun maybe (open and smell), alternatively some enthusiastic chemical reaction (if there was too much water and they got pally with each other - strange stuff happens!), or else - the packaging has wierd ideas, I've seen it lots of times before this.

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Asked by Michael Marshall
on 2009-07-01 17:28:59

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Thinking person's crumpet

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Answered by Ned Edwards
on 2008-12-03 16:35:00

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I suggest it's is a reversible rising reaction. Rising agents are a mix of sodium bicarbonate and an acid. Some of the rising is due to reaction starting at room temepersture due to wetting the powder, so bringing the two components in contact. That reaction would not be reversible and would probably be already complete at the start of baking.BUT if there is excess sodium bicarbonate, some would survive into the higher temperature baking period. Above 60C it starts to to decompose:2NaHCO3 â†’ Na2CO3 + H2O + CO2This probably helps form a fine bubble texture in the crumpets, because there isn't time for them to coalesce in the thickening dough.When the crumpets cool again to below 60C the reaction goes into reverse, very slowly reabsorbing the CO2 from the bubbles. This creates a slight vacuum in the porous gas-pockets of the crumpet, which suck in air from the surrounding gas in the encapsulation. If you put the pack in boiling water for some time, the bicarbonate should slowly decompose again, partly restoring the pack to the as-bought size.

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Asked by Michael Marshall
on 2009-07-01 17:28:59

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Thinking person's crumpet

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Answered by Dave
on 2008-12-05 13:22:00

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I've noticed something very similar with supermarket bought beef mince. The mince was packaged in a plastic tray, sealed with a cellophane (or similar) lid. After a few days in the fridge (not freezer), I noticed that the whole package was slowly 'scrunching', while the mince itself turned grey in colour. After a week the appearance of the package was as if it had been vacuum packed, with the tray and lid now 'hugging' the mince. Unfortunately, the meat was now outside of its use-by date, and had to be discarded.The only clue I can offer is that the meat was 'Packaged in a protective atmosphere', which implies the airspace in the package may not have been air.

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Asked by Michael Marshall
on 2009-07-01 17:28:59

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Thinking person's crumpet

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Answered by Stewart
on 2008-12-09 23:46:00

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There tends to be a general feeling that food packaging of this sort will not allow water to escape. This is not true. Over time, OH ions will certainly migrate across a thin plastic film and I think that this is what is happening. Crumpets have a high water content and so it is going to be fairly humid inside the package. The humidity in a freezer is low, all the water has formed frost and ice. This is an ideal environment for the water in the package to slowly migrate across the plasic film resulting in the contents shrinking as they dehydrate.This is one reason why freezer bags are thicker than standard sandwich bags.

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Asked by Michael Marshall
on 2009-07-01 17:28:59

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Thinking person's crumpet

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Answered by Michael Marshall
on 2009-07-01 17:28:36

(1 vote) average rating:5

Our thanks to Warburtons, the company that made these crumpets, for the following - EdWarburtons crumpets are a short shelf-life, high-moisture product and as such, are particularly susceptible to food spoilage organisms. The product is packaged in a carbon dioxide environment to extend the shelf life and to protect the crumpets against microbial spoilage, particularly aerobic organisms.Over time, the carbon dioxide gas is absorbed by the liquid in the product, and as it takes up less space in liquid form this reduces the internal pressure of the package. As long as the seals are intact, the differential in pressure means the packaging contracts. The lack of spoilage in the product is an indication that the seals are intact and the integrity of the product remains unaffected.Claire Minzey, Clarion Communications, London, UK

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Asked by Michael Marshall
on 2009-07-01 17:28:59

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Thinking person's crumpet

Editorial status: In magazine.

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Answered by MarijaNova
on 2009-07-02 10:47:38

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There is always a possibility that you have altered the structure and permeability of plastic with freezing and warming again if the product was not meant for freezer. And combined with different pressure, higher solubility at lower temperatures, humidity, chemical and biochemical reactions you end up with flattened crumpets.

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