(Rodrigo Cunha/)
What the legend says: Long-life milk not sold within the expiry date would go back to the factory and be repasteurized to gain more shelf life. A number at the bottom of the box would indicate how many times this process has been done.
The truth: This story is nonsense. The number on the box exists, but it is only used for companies to control packaging batches and can be found on many products. Another error in the legend is to say that long life milk is pasteurized. In fact, it goes through a process called UHT, ultrapasteurization. Pasteurization raises the temperature of the milk to 75ºC and kills only the most harmful microorganisms. UHT maintains the milk at 120ºC, eliminating all microorganisms. See below what would happen if the milk was “repasteurized”.
1. Milk has several microorganisms. Pasteurization only kills those most harmful to our health. That’s why pasteurized milk has a shelf life of 48 hours. The ultra-pasteurized lasts six months
two. The dead microorganisms release enzymes that begin to act on the milk proteins. If this happens within the allowed time, there is no problem – it is even good for our body, as it improves the digestion of milk
3. The problem is if the enzymes are in contact with the milk for more than the allowed 48 hours. Then the acidity level increases a lot and the milk starts to form lumps – small blocks of solid particles.
4. Repasteurizing the milk would not kill more microorganisms, as the temperature of the process would be the same. Furthermore, the enzymes of the “dead” would have more time to form solid blocks and the milk would go to the stores looking like ricotta. Yuck.