Dr Nicola asked:
I have two related questions:
1. It has been suggested that the Vikings extracted cod liver oil by "fermenting" liver (the raw livers were emptied into open vessels and left there, and when the weather grew warmer, the cod liver oil separated from the livers and floated up to the top and was skimmed off). My question is this: is it possible to ferment liver? I would have thought that the main process involved was "putrefaction", with possibly very minor fermentation taking place as a result of glycogen reserves within the liver.
2. I am aware that certain cultures, for example the Sudanese, produce a dish called 'Miriss' that is supposedly fermented fat. And during arctic expeditions, they would tie up seal blubber in a bag made of seal carcass and let it ferment. My question is: can fat really ferment and change in structure?
I look forward to your reply.
All over the world, cultures will ferment various different food stuffs in order to make them taste a bit more interesting.
So the actual process of fermenting usually involves some kind of living organism like a yeast or a bacterium, and it also involves an anaerobic environment, so no oxygen. I couldn’t find very much information about the Viking method of making cod liver oil, but it does seem that they just dumped a load of cod livers into a barrel, left it in some seawater and then just left it outside. Presumably, what would happen is that you would have bacteria that would break down the liver, and because oil isn't quite so easily broken down - and this is a serious problem that the sea actually has - the oil would float to the top, and it won't be broken down as quickly as the other parts of the liver.
When it comes to fats and Inuit wrapping up bits of fat in seal skin, what was probably happening there is that you have certain types of bacteria, probably Bacillus bacteria which will break down bits of the fat, make it decompose and make it taste quite different.
Interestingly, about a year ago, just after Christmas, Yorkshire Water actually released a load of Bacillus bacteria into the sewers because one of the major problems that we have with Victorian sewers in this country is that people pour a lot of fat down the sink and it builds up into great big lumps, and blocks up the sewers. So what the water company did was they flushed a load of bacteria down there to break it all down.