Pasteurised, UHT and sterilised milk compared

Pasteurised, UHT and sterilised milk are all heated to reduce or destroy microbes. They differ in how hot, how long, and how the milk is packed afterwards. Pasteurised milk is milder and must be kept cold. UHT and sterilised milk are heated harder, sealed in clean packs, and can be kept at room temperature until opened. Thai rules define each one.

What each heat treatment is

The Thai definitions are in Ministry of Public Health Notification No. 350 of 2013 on cow milk.

Pasteurised. Heated to at least 63 degrees Celsius for at least 30 minutes, or to at least 72 degrees Celsius for at least 15 seconds, then cooled at once to 5 degrees Celsius or lower. Codex Alimentarius, the international food code, gives the same two conditions as the minimum effect for pasteurisation.
UHT. Short for ultra-high temperature. Heated to at least 133 degrees Celsius for at least 1 second, then filled into packs under sterile conditions. The milk must also be homogenised, meaning the fat is evenly mixed. Codex describes UHT as normally 135 to 150 degrees Celsius, and says it is designed to leave the milk commercially sterile.
Sterilised. Milk sealed in its container, then heated to at least 100 degrees Celsius for a suitable time, and homogenised. The milk is sterilised inside the pack.

Because the pack, the treatment and the storage are linked, Thai rules also require the name on the label to state the treatment. A pack should therefore say pasteurised, UHT or sterilised.

How each must be stored

Pasteurised or fresh milk. The Thai notification says it must be kept at 8 degrees Celsius or lower from filling until it reaches the consumer. The consumption period must not exceed 10 days from the date of filling, unless the producer has quality controls approved by the Thai Food and Drug Administration (Thai FDA) for a longer period. Thai FDA gives the same advice for bagged pasteurised milk: keep it in the fridge at no more than 8 degrees Celsius, for about 10 days from filling.

UHT and sterilised milk. The notification says they are kept at normal temperature. The maker must hold each batch for at least 5 days at normal temperature after filling, before release, to check that the milk has not changed.

How long each keeps

Thai FDA gives approximate times for unopened packs:

pasteurised bagged milk: about 10 days from filling, kept at 8 degrees Celsius or lower
UHT carton milk: about 6 months at normal temperature, away from direct sun and not stacked too high
sterilised canned milk: about 12 months without chilling, away from direct sun

Codex puts the job of setting shelf life on the manufacturer, so the date printed on the pack is the one to follow.

After opening

For bagged pasteurised milk that is not finished, Thai FDA advises pouring off the portion to be kept and drinking it soon. A Clemson University extension fact sheet from the United States says an opened UHT pack should be treated like fresh milk and used within several days. That is a United States source, and no Thai figure for opened UHT milk was found.

In short

Pasteurised milk: at least 63 degrees Celsius for 30 minutes or 72 degrees Celsius for 15 seconds, then cooled to 5 degrees Celsius or lower.
UHT milk: at least 133 degrees Celsius for at least 1 second, sterile filling, homogenised. Sterilised milk is heated in its sealed pack.
Thai rules: pasteurised milk is kept at 8 degrees Celsius or lower and used within 10 days of filling unless approved otherwise.
UHT and sterilised milk are kept at normal temperature, and Thai FDA gives about 6 months and about 12 months for cartons and cans.
After opening, use milk soon. A US extension source treats opened UHT milk like fresh milk.