nevetsjc80 said:
I was wondering, back in my army cadet days when the british army ration packs came with tinned main meals, I remember being told that when you heat the can (ie half submerge the can in water and bring to the boil as decribed on the menu sheet) you cant use the water for a brew something to do with the zinc on the outer tins.
Any how now the ration come in the foil type packets can you boil them in the bag and use the water for a brew?
Steve
There is a real risk of tin and zinc poisoning from the older style of tin cans (un-coated) used in conjunction with high-acid foods, like tinned fruits, tomatoes. The risk is increased if the can is dented or scratched as this can expose uncoated tin to the acid in the food.
In an experiment for the WHO (The toxicity of tin in canned fruit juices and solid foods 1971) a group of volunteers drank tinned concentrated orange juice with 703ppm (parts per million) of tin experienced no effects but after the orange juice was pasteurised by heating and stirring in the tin can, the measured ppm was found to be 1370, this caused nausea and/or diarrhoea.
No adverse effects were noted in 9 volunteers fed a C-ration diet consisting of canned fruits and meats which had been stored for 20 months at 37°C (Calloway & McMullen, 1966). The tin content in the food ranged from 254 to 538 ppm, expressed on the basis of dry solids. It was estimated that these subjects consumed an average of 163 mg of tin per day (ranging from 116 to 203 mg/day) and that virtually all of the ingested tin was recovered in the faeces. Nitrogen absorption from the gastrointestinal tract was decreased, suggesting that the tin in the food was associated with protein as an indigestible complex, as previously proposed by Goss (1917). C-rations stored at 1°C for 20 months contained less than 50 ppm tin, and also produced no adverse effects in the volunteers.
Now the foil pack, in modern longlife food according to the data on manufacturing specification, is made up of three ply bonded under pressure. Comprising of an inner layer of polyester at 0.005mm thickness, an aluminium layer of 0.010 mm thickness and an outer layer of polyethylene 0.0051mm. That is designed to keep the food away from the aluminium, and the aluminium from the heat source. I dont know is this is still the case today, but the American MRE packs are of a similar construction
