Why can you only store an open box of juice for a day?
Opening the box, you broke the tightness of the package and let various bacteria inside the juice. If it is stored in the refrigerator, the growth of bacteria slows down, if it is on the table, it deteriorates many times faster, since bacteria begin to multiply actively. Therefore, the maximum can be stored juice for three days, then it begins to become bitter and unpleasant to the taste.
No, this is not a trick. If the juice has deteriorated in such a short period of time, then it is natural. Well, if it costs a month, but it is written that it is a day, then it's just that - for show.
If the fresh is left for a few days, it will deteriorate. And regular juice will stand for a long time. It makes you think!
Of course, packaged juice will not spoil in a day if you drank it by pouring it into a glass, and not "from the throat", and at the same time it is not hot in the room. Read the composition of the juice, there is probably sugar (sugar syrup) and citric acid (sometimes without it). These substances are preservatives that every housewife, engaged in harvesting for future use, uses in the kitchen. In addition, the packaged juice was subjected to heat treatment, that is, it boiled over, which means that it does not contain bacteria and air. So keeping it in the refrigerator for 1 day is just a precaution. Another thing is that after 3-4 days in the bag, mold can grow on the walls. You may not feel the taste, as the mold will be on the juice-free walls, but when you drink the juice and pour it into a glass, the mold spores will get into the liquid together. Therefore, I advise you to store the juice for more than 1-2 days, I advise you to pour it into a clean can.