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New Scientist Last Word Blog

A little while ago we froze a packet of those pancake like products that in these parts we call crumpets. At the time,
card against humanity, 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,
cards humanity, 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,
cards against humanity expansion, yeast, raising agents, E450, E500, salt, sugar, preservative, calcium propionate. What’s going on?

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Was it very warm when you put them in there? air expands when it is warm, maybe when it went in the freezer it shrunk as the air got cold. I’m no expert though, it was just a thought. 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.

By Sabrina. on November 30, 2008 5:40 PM

Yeasts break sugars down to water and carbon dioxide,consuming oxygen and in the process making some unintended hydrogenperoxide,
cards against humanity card game, which must be removed using catalase. The hydrogen peroxide is broken down bythe catalase in yeast, in this reaction: 2 HOOH > 2 H2O + O2I 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. 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. 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.

By Martin on December 03, 2008 8:15 AM

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. 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.

By Ned Edwards on December 03, 2008 4:35 PM

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.

By Dave on December 05, 2008 1:22 PM

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.

By Stewart on December 09, 2008 11:46 PM

Our thanks to Warburtons, the company that made these crumpets, for the following Ed

Warburtons 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

By Michael Marshall on July 01, 2009 5:28 PM

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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