Another kitchen debate…Consider one of those half-gallon boxes of Orange Juice with a twist-off cap on the lid. To get things started you have to twist off the cap and then pull out a small round plastic seal.
Once you’ve done this, poured a small glass of juice, and securely replaced the cap, are you materially affecting the shelf life of the product? Someone has suggested that ‘once its open it starts deteriorating’. While I admit you’re lettiing in a little of your kitchen’s air, and there’s now a bit more air in there then there used to be, I’m hard pressed to see how its going to spoil any sooner.
Packages are hermetically sealed at the factory. Once you’ve broken that seal(the hiss when you peel off the seal), it’s no longer airtight, even with the screwcap. Air hastens deterioration; however it was already deteriorating anyway, hence expiration dates. The seal keeps it (as) fresh (as possible) up until you use it, provided that is before the sell-by date, after which you’ve got a finite amount of time before spoilage. Unless your kitchen is a cleanroom.
Orange juice is pasteurized to kill off most of the microbes present from harvesting and processing. Not all are killed, which is one reason why even pasteurized, sealed foods will eventually go bad, but exposing it to your kitchen air introduces more mold spores, bacteria, etc., which may decide to set up shop in your OJ container.
Good point. In addition to age and oxidation, the other contributor to spoilage is simple exposure to mold and bacteria in the air. Nothing pathogenic at refrigerator temperatures, but definitely cuts back the life span of any food item you open or touch with your fingers.