🔄 Condensing

Condensing is the partial removal of water from milk. The water is evaporated under vacuum in film evaporators: at reduced pressure milk boils at just 65–70 °C, and it is not heated any higher so that its flavour does not change. The Codex Alimentarius distinguishes two products: sweetened condensed milk and unsweetened condensed milk (evaporated milk).

Sweetened condensed milk, under the Codex and EU rules, contains at least 8% milk fat and 28% milk solids; it is about 45% sugar. Sugar binds water so that microbes cannot get enough of it, and the product preserves itself. It contains more lactose than can dissolve, so finely ground lactose — about 0.05% — is added during rapid cooling, and the crystals stay too small to notice. Evaporated milk (at least 7.5% fat and 25% milk solids) keeps thanks to sterilisation in a sealed can or UHT treatment with aseptic filling.

Condensing milk under vacuum was patented by the American Gail Borden on 19 August 1856. Long simmering of milk with sugar also gives dulce de leche and cajeta, and in India khoa; for kulfi, too, the milk is first boiled down. Winemaking has a similar technique: in the EU, concentrated grape juice is obtained by partial dehydration without caramelisation.

Why it matters to you. In the EU, the label of condensed milk has to state the proportions of milk fat and milk solids-not-fat — they show whether it is the genuine product. 100 g of sweetened condensed milk has about 321 kcal, evaporated milk 134 kcal (USDA). Unopened cans keep almost indefinitely at 0–15 °C: in the warm the product turns brown, and in the cold the protein may settle out.