Tinplate + Milk

[mikemaz]

Hi im just doing research and was wondering since its possible to store soft drinks such as coke and pepsi is it possible to store milk in a tinplate storage like the cans used in carbonated drinks?

thanks
mike

[theprof]

The answer to this is both yes and no!

Yes it is possible to can milk in tinplate cans. Think of Carnation evaporated milk and Ideal milk, both of which are forms of sweetened, condensed milk. However, both these products have a reduced water content..

The reason why conventional milk cannot be canned is down to the canning process itself. Canned products are boiled in situ in the can either before or after the lid has been put on. This boiling kills all the bacteria in the foodstuff and the lid prevents further ingress of bacteria.

Boiling milk caramelises many of the sugars it contains and the taste and texture of the milk changes. It's an unmistakable taste even after cooling and it tastes far worse from a can than a saucepan.

Many years ago cane sugar (sucrose) was added to milk before canning in order to try to counteract this taste change. However, the process never really took off but it did give the canners the idea of evaporating the water out of the milk first. This is why condensed milk has a high sugar content - without the sugar it's not very nice at all.

Milk also encourages the leeching of metallic ions from the inside wall of the can which is why it's important to transfer it to a non-metal container in the fridge after opening apart from the risk of bacterial colonisation. Having said that, the sugar in condensed milk, slows this leeching down considerably and nowadays, most cans are lined to try to prevent this occurring.

[mikemaz]

hey thanks for the reply ok so i see it wouldnt be a good idea to store milk in such containers. I do have one more question; what if the milk was stored in a tinplate container that wasnt as air tight as a can of coke but with a screw cap would that still not work ?

[theprof]

No, it still wouldn't work and as it would be even worse than the first case as far as spoilage was concerned.

Assuming that we're talking about conventional, pasteurised milk, it should be remembered that pasteurisation is not all what it's made out to be. Although it kills many harmful bacteria such as those that cause tuberculosis, it doesn't kill all micro-organisms.

When milk goes off, there are a specific series of steps that happen as far as micro-organism growth and colonisation are concerned. First of all bacteria called streptococci convert a sugar called lactose to lactic acid. The acidity of the milk then rises. Then other bacteria called lactobacilli start growing at a tremendous rate and convert even more of the lactose to lactic acid. The acidity of the milk then rises even more. Under these conditions, mould, yeasts and other fungal organisms begin to grow and these organisms reduce the acidity. Then other bacilli start to multiply and these convert proteins in the milk to ammonia. The milk then becomes more alkaline and this combined with the destruction of enzymes leads to sour or decomposing milk.

So where do these bacteria come from? Well, they are present in the air, your fingers and hands, on pet hair that may be circulating in the room and suchlike. Pasteurisation of the milk may well have killed off many of the micro-organisms in the raw milk, but it cannot protect the milk afterwards. In addition, once milk reaches suitable temperatures, the micro-organisms that were not killed by pasteurisation begin to grow and multiply anyway. So milk can go off in an unopened, sealed container at room temperature.

So the type of stopper on the container is really immaterial. The only way to prevent micro-organism growth in a household environment is by reducing the ambient temperature to that of a fridge. Although bacteria, yeast and mould organisms are not all killed in milk at fridge

[theprof]

temperatures, the microorganisms become torpid and are unable to grow and multiply.

[mikemaz]

thank you very much i hadnt considered ANY of the points you mentioned and i feel a bit like a silly designer.