Whole, semi-skimmed, filtered, UHT or raw — which milk should I use?

Almost every milk on the shelf is the same liquid with a different amount of fat removed and a different amount of heat or filtration applied. Knowing which of those two variables has been changed tells you what it will do in a pan and what it will taste like in a cup of tea.

Safety

Step by step

1. Choose by fat for cooking.Whole milk for anything where the milk contributes texture — custards, ice cream bases, panna cotta, rice pudding, porridge, milk-poached fish. Semi-skimmed is acceptable for sauces thickened with flour. Skimmed is a compromise everywhere.
2. Choose by heat treatment for flavour.Pasteurised and filtered milks taste like fresh milk. UHT and sterilised do not, and the difference is most obvious in tea, coffee and anything uncooked. In a curry or a bake, UHT is undetectable.
3. Use filtered milk if you waste milk.The extended life is the entire point and it is a real one — a fortnight unopened and around a week after opening is typical. It costs more per litre and saves more than that if you regularly pour milk away.
4. Watch the pan more closely with low-fat milk.Skimmed and semi-skimmed catch and scorch more readily, because there is less fat between the proteins and the hot metal. Heavy pan, lower heat, and stir.
5. Understand what heating does to any of them.A skin forms because proteins coagulate and dry at the surface. Milk boils over because that skin traps steam beneath it until it lifts suddenly. Both are prevented by stirring, covering, or keeping it below a boil.
6. Keep the allergy and intolerance distinction clear.Lactose intolerance is an enzyme shortage and lactose-free cows' milk solves it. Milk allergy is an immune reaction to the milk proteins, and lactose-free milk is still dangerous for it. Only plant milks avoid the proteins.

Tips

• Milk freezes well, though whole milk separates slightly on thawing — shake it hard and it recombines. Freeze it in the original container with a little poured off, because it expands.
• The colour codes are conventional rather than legal, but they are near-universal in British supermarkets: blue whole, green semi-skimmed, red skimmed, gold Channel Island.
• For frothing in coffee, semi-skimmed foams to the greatest volume and whole gives the most stable, silkiest microfoam. Skimmed foams big and collapses fast.
• A splash of UHT in a store cupboard is worth keeping for emergencies. Once it is in a sauce or a bake, nobody can tell.
• Milk that has gone slightly sour is not dangerous if it was pasteurised — it is soured rather than spoiled — and it is excellent in soda bread and scones. Milk that smells foul or has separated into curds and yellow liquid goes in the bin.

Alternatives

• Whole milk — around 3.6% fat: Blue top. The default for cooking. The fat gives body, prevents sauces from tasting thin, and makes custards and porridge substantially better. Nothing else on this list is a full substitute for it in a recipe.
• Semi-skimmed — around 1.8% fat: Green top, and the most-sold milk in Britain. Fine for tea, cereal and most everyday use. In cooking it makes thinner sauces and less rich custards, and it foams less well for coffee.
• Skimmed — around 0.1% fat: Red top. Very little body. It works in a béchamel because the flour does the thickening, but it makes a poor custard or panna cotta and it scorches more readily because there is less fat protecting the proteins from the pan base.
• Filtered or microfiltered milk: Ordinary pasteurised milk passed through a fine filter that removes most remaining bacteria. Keeps unopened for weeks rather than days and lasts noticeably longer once open. Tastes the same as its unfiltered equivalent and behaves the same in cooking. Sold in each fat grade.
• UHT and sterilised milk: Heated far higher than pasteurisation, so it keeps unrefrigerated for months. The heat caramelises some of the lactose and denatures proteins, giving a distinctly cooked flavour. Perfectly usable in cooking where other flavours dominate; noticeable in tea and coffee.
• Channel Island or Jersey milk: Around 5 per cent fat, gold top. Richer and slightly sweeter, from Jersey and Guernsey herds. Excellent in custards, rice pudding and anything where the milk is the point.
• Lactose-free milk: Ordinary cows' milk with the enzyme lactase added, which splits lactose into glucose and galactose. It is real dairy and behaves identically in cooking, though it tastes slightly sweeter because those sugars are sweeter than lactose. It is not suitable for a milk allergy, only for lactose intolerance.
• Raw milk: Unpasteurised, sold direct from the farm in England, Wales and Northern Ireland and banned in Scotland. It tastes of the farm it came from and its supporters value that. It also carries a real and documented pathogen risk that pasteurisation exists to remove.

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