Laying it on thick: Swetha Sivakumar on condensed milk

A can of condensed milk didn’t last long in our house, once it was opened. My mother would use about half in some dessert, and carefully put away the rest. But before she could return to it, my sister and I would have taken a spoonful each time we passed the refrigerator, and the can would be scraped clean.

The creamy texture that makes condensed milk so tempting, and so useful in desserts, is no accident.

Sweetened condensed milk or SCM is a viscous suspension of sugars (sucrose and lactose), milk fat and protein. Invented in 1856 as a way to keep regular milk from spoiling, it is made by heating milk under a partial vacuum so that it boils between 43 degrees and 60 degrees Celsius. The vacuum chamber is important because this accelerates evaporation and prevents the scorching of the milk, thus avoiding the “cooked milk” flavour that would otherwise result.

The milk is allowed to simmer in this manner until about 60% of its water content evaporates.

Sugar is added, for sweetening and as a preservative. Incidentally, sugar accounts for nearly half the volume of condensed milk (45%; I don’t eat it by the spoonful any more).

This much sugar should threaten the creamy texture, since sugar molecules love to bind with each other to form crystals. Lactose-sugar crystals, in fact, would be particularly gritty on the tongue.

To keep these from forming, condensed milk is allowed to cool, then seeded with lactose crystals too tiny to detect on the tongue. The presence of the very tiny crystals gives new crystals something to cluster around; the resultant crystals are still too tiny to detect on the tongue, and so the creaminess stays intact.

It’s not just the texture that makes SCM useful in desserts; it is also resistant to curdling. Key lime pies, for instance, can be made with it.

This is because condensed milk undergoes a process called forewarming, prior to condensation. This involves heating and holding the milk at certain temperatures to make the casein molecules more tolerant to fluctuations in heat and acidity levels.

All the processing it undergoes makes SCM behave quite differently from milk in the freezer too. The combination of high sugar and concentrated milk proteins depresses its freezing point to -15 degrees Celsius, from about -0.5 degrees Celsius for regular milk.

Add it to homemade ice-cream and the result is creamier and softer on the tongue. This is because most home freezers are set to -18 degrees Celsius. Regular milk becomes solid, like a brick, at that temperature. Crystals have long formed; the resultant ice-cream is often just a bowl of fast-melting shards. Ice-cream made with condensed milk, however, remains soft and scoopable.

My favourite summer recipe? An easy dessert of SCM, whipped cream and flavourings such as vanilla or pureed mango. Just fold the ingredients together and place the mix in the freezer. In four to six hours, it’s a soft, scoopable ice-cream, ready to be served.

(To reach Swetha Sivakumar with questions or feedback, email [email protected])