Dairy is not one group where shelf life is concerned: products lasting a few days sit on the same shelf as products lasting months. The first variable is heat treatment. In pasteurised products some organisms survive and life depends on the cold chain; in long-life products the heat treatment is more severe and, unopened, the product keeps at room temperature.
| Product | What sets its life | If temperature slips |
|---|---|---|
| Pasteurised milk | A steady cold temperature is assumed | A few hours of warming leave less life than the label states |
| Yoghurt and fermented products | Acidity | Fermentation continues and the product turns sour; a quality limit |
| Fresh cheese | High moisture | Depends entirely on the cold chain |
| Matured cheese | Low moisture | The rate of ripening changes |
The type of date on the label also follows the product. For food that is highly perishable from a microbiological point of view and could soon endanger health, a use-by date applies; in the EU food is deemed unsafe after it (Regulation 1169/2011, Article 24). For other products the best-before date is about quality.
Light is a loss of life independent of temperature. In a Virginia Tech study, 2% milk in glass and translucent HDPE bottles oxidised within four hours under LED lighting of 1068 lx.
If life comes in shorter than expected, measure three places in order: cooling speed after filling, peak temperatures in distribution and the retail cabinet. Changing the formulation before measuring those three is usually looking in the wrong place.
