Question 1: Why do banana skins by themselves, bereft of the fruit they originally contained, get so black so fast?
Observationally I know that the full banana itself ripens quickly, although I don’t know why, and I suspect the two answers are linked.
Question 2: A carton of cream, opened or closed, stays fresher so much longer than a carton of milk, open or closed. Why is that?
Although I mainly want to subscribe (yes I know you don’t need to post), I will note that the “sell by” date of milk products increases as the milkfat increases, so that 1% spoils faster than 2%. I’d like to know why, too.
The cream is ultra-pasteurized.
thelurkinghorror, I have always found that the higher the fat content of milk, the faster it spoils. I’ll have to go experiment.
I’m going by sell-by dates, not experience. I haven’t compared them really.
Banana skin get black because an enzyme in them catalyzes the production of a black compound. this reaction needs oxygen - once you peel off the skin of the banana, oxygen can get to the site of the reaction.
Bananas ripen very quickly because they are normally shipped unripe, and ripening is induced by treating the fruit with ethylen gas, which is the plant hormone that induces ripening.
Nice cite/site. Thanks. When you say “into the site of the reaction” you mean that now that banana-peel site for reaction is being exposed on both sides to oxygen, thus enhancing and quickening the process?
Sell by dates on a shelf are highly unreliable markers of how long a product lasts from creation, to spoilage.
The 2% may be from a different batch than skim, 1% or whole, or they are all from different batches. Demand in the market, or poor rotation could cause today’s delivery of whole milk being put on the shelf today, and yesterday’s makes it to the shelf tomorrow.
Back in the olden days of my time in the dairy department, the milk cooler was often very full at delivery time, and though we did our best to rotate properly, often a case stack could be accidentally pulled out of order, especially if the cooler was full, space for the dolly was at a premium, and 2 dates were right next to each other, or half a stack had a different date code.
As for the banana skins, when you open the skin, you’re damaging it in multiple directions. The tears are now open to oxygen, the skin has been folded back, damaging the cells, and now the inside is exposed to oxygen. Before peeling, it was “sealed.” After peeling, it’s as unsealed as possible.
Funny enough, nowadays the use-by date on milk cartons is about the only accurate date in the grocery store. It will generally turn bad within a day of the date. I think the variation in the length freshness between different fat percentages of milks is simply the date that the milk comes into the store and is sold by; in other words, maybe the 1% doesn’t move as quickly as the 2% so the cartons you see have a sooner use-by date than the newer shipment of 2%.
I have found this from the estimable food board chowhound.com, posted by embee Mar 31, 2007 at 04:12PM,* from a thread very similar to this (here I duck from rotten eggs and catcalls from the TM re necessary pre-research). As** needscoffee** called it, ultra-high pasteurization, and milkfat are what make the difference. Their thread also has a subsection on lactose-removed milk, which also lasts much longer than regular milk; yet another poster at chowhound mentioned that butter–the highest milk-fat product of them all–in the fridge will last practically forever, as an ultimate example of it’s the fat. So thelurkinghorror is also right. Cool, huh?
I’d like to respectfully ask something to those in this thread who espouse the sell-by-date theory. It seems to me that the premises of stock rotation, sales frequency of 2% over 1%, etc., is perfectly correct regarding milk, but not cream, which surely has a slower sales frequency to begin with. Did I understand you correctly?
Anyway, embee’s post: We certainly agree on the taste and utility of UHT cream. Although I haven’t kept a tally of spoilage rates, my experience these days is roughly:
UHT whipping cream (35% BF) keeps indefinitely after best before date unopened; keeps at least 4 weeks after best before date once opened.
Non UHT whipping cream (32%-35% BF) turns within 3-5 days of best before date, whether opened or not.
UHT half & half cream (10% BF) keeps indefinitely after best before date unopened; can be used for many weeks - usually well over a month - after best before date once opened.
non-UHT half & half cream (10% BF) keeps for about a week after best before date whether opened or not.
Milk (we use 2% and 3.25%) keeps for about a week after best before date whether opened or not.
Lactose free milk is all UHT and seems to last indefinitely, though it sometimes clumps after months of storage
UHT milk is only available in tetra paks
*This poster is still active on chowhound. I have not yet asked/thanked him for appropriating this post. I can’t figure out the site’s layout yet.
My milk goes bad either on the date or a day or two before. My fridge is at the correct temperature verified by a refrigerator thermometer, but I keep it in the door, which is less cold than the rest of the fridge. When I worked in a lunchroom last year, the milk would go bad literally on the date stamped. You could set your calendar to it, if such a thing were possible. The milk was kept at 37 degrees F.