Question 1

What is the difference between pasteurised, UHT and raw milk?

Accepted Answer

The difference is how much heat the milk has been through, and that determines both safety and how long it keeps.

**Raw milk** is unheated, straight from the animal after filtering and chilling. It retains whatever microorganisms were present, which is the point for its advocates and the objection for public health bodies. Raw milk can carry *Salmonella*, *E. coli* O157, *Campylobacter* and *Listeria*, and outbreaks are documented regularly. It is banned or heavily restricted for retail sale in many countries and jurisdictions. Health authorities generally advise against it entirely for children, pregnant women, older people and anyone immunocompromised. Claims that it retains significantly more nutrients are not well supported — pasteurisation causes only modest losses, mostly of some B and C vitamins that milk is not a major source of anyway.

**Pasteurised milk** is heated enough to destroy pathogens without sterilising. The common method, **HTST** (high temperature short time), heats to around **72°C for 15 seconds**. This kills the organisms that cause disease and most that cause spoilage, giving a fridge life of one to two weeks. Flavour is close to raw. This is standard supermarket milk.

**UHT (ultra-high temperature)** heats to around **135–150°C for a few seconds**, then packages it aseptically. This is effectively sterilising, so unopened cartons keep for months at ambient temperature — which is why UHT dominates in hot climates and countries with long distribution chains.

**Why UHT tastes different.** The high heat drives Maillard reactions and denatures whey proteins, producing a faintly cooked or caramelised note and a slightly different mouthfeel. Once opened it must be refrigerated and behaves like ordinary milk.

**ESL (extended shelf life)** sits between the two.

**Homogenisation is separate** — it breaks up fat globules so cream does not rise, and has nothing to do with heat treatment.

Question 2

What makes milk froth properly?

Accepted Answer

Protein, not fat — milk proteins unfold at the air-liquid interface and stabilise the bubbles, which is why skimmed milk actually froths more easily than whole, contrary to expectation. The

Question 3

What is yoghurt, and how is it different from other cultured dairy?

Accepted Answer

Milk fermented by specific bacteria that convert lactose into lactic acid, which lowers the pH until the milk proteins coagulate — producing thickness from chemistry rather than from anything added.

Question 4

Why does milk boil over when water does not?

Accepted Answer

Because milk forms a skin, and that skin traps the steam trying to escape. When water boils, bubbles of vapour form, rise and burst freely at the surface. Nothing holds them, so water can boil

Question 5

What is the difference between "best before" and "use by"?

Accepted Answer

Use by is about safety. Best before is about quality. Confusing them causes both unnecessary waste and genuine risk, in opposite directions. Use by appears on foods that become unsafe as they age,

Question 6

What actually causes food poisoning, and which pathogens matter?

Accepted Answer

A small number of organisms account for most cases, and they behave differently enough that the same precaution does not work for all of them — which is why general advice to "cook things properly"

Question 7

Where should food actually go in a fridge?

Accepted Answer

Placement matters for two separate reasons — temperature varies within a fridge, and cross-contamination runs downwards — and getting the second wrong is the one that causes illness. The temperature

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