It is a little known fact that unlike almost all canned products, sweetened condensed milk is not cooked in a retort. It is made from pasteurised condensed milk and sugar that is canned in aseptic conditions. But the canned product is not cooked after canning. The safety of the food is assured by the low water activity brought about by the extremely high sugar content. This prevents any bacteria present from growing.
Just out of interest, canned anchovies are also not cooked – or retorted as we in the business (more correctly, we who used to be in the business) say – because they would go to mush. Their safety is also assured by lowering the water activity to a level that will not allow microbes to grow, this time with salt and oil. Science!
What happens when you cook sweetened condensed milk is really cool.
If you don’t burn it, you get caramel.
The best and safest way to do this at home is to cook an unopened can in a slow cooker. The way it used to be done by boiling a can in a saucepan on the stove often resulted in the pot boiling dry untended, and the can exploding. It was important to top up the pot with boiling water every so often. With the lid on, the slow cooker will not boil dry.
This can of condensed milk was cooked on high for ten hours. I intended it to cook for only 6-8 hours but I forgot about it. No harm done. The result was a rich butterscotch tasting caramel.
Just look at that glorious colour.
If you live in the Kimberley or some similarly outrageously hot place, you can also make caramel by leaving a can of sweetened condensed milk on the dashboard of your car for a couple of days.