[paul.fr]

Orange juice contains lots of sugar, if you were to leave it unrefrigerated would the sugars turn to alcohol?

[dentstudent]

I've made cider with cartons of apple juice - you add yeast and a bit more sugar. I think therefore that the sugars in the orange need something to react with?

[DoctorBeaver]

I've made cider with cartons of apple juice - you add yeast and a bit more sugar. I think therefore that the sugars in the orange need something to react with?

Vodka?

[Bored chemist]

I can't turn orange juice into alcohol; but I know a yeast who can.
You can ferment just about anything with sugar in it; the product may not be worth the effort for example my garlic wine didn't seem popular.

Without the yeast (or at least the enzymes the yeast makes) no fermentation will happen. Cartons of juice are sterilised before they are sealed. Freshly squeezed orange juice probly contains wild yeasts that will do the job.

[neilep]

I can turn it into wee wee !!!

[another_someone]

I can't turn orange juice into alcohol; but I know a yeast who can.
You can ferment just about anything with sugar in it; the product may not be worth the effort for example my garlic wine didn't seem popular.

Without the yeast (or at least the enzymes the yeast makes) no fermentation will happen. Cartons of juice are sterilised before they are sealed. Freshly squeezed orange juice probly contains wild yeasts that will do the job.

One question I would have - is there an ideal pH for the yeast to act, and if so, how does orange juice measure up to that pH?

[chris]

Fruit, upon which yeast naturally lives, tends to be quite acidic anyway - oranges are rich in citrate, apples contain lots of malic acid - and so yeast is quite acid tolerant; at least as far as I know. (And judging by the standards of some of the "vinegar" that passes as "home-made wine" (and which I have had the dis-pleasure of tasting), it's possibly even more tolerant than I first thought)

[eric l]

As far as I know, the yeasts for the fermentation of grape juice and apple juice into ethanol are living on the skin of this fruits. 
It is possible that there are similar yeasts on the skin of oranges - if you can have them fresh from the tree.  But the skins are treated for storage and transport, so I am almost sure that any yeast will be disactivated.  So you will need some "starter" (mix of yeasts and sugars) available wherever they sell what is needed for home brewing or home wine making.
Untreated orange juice (= no pasteurization and no additives) will start to ferment, through action of "wild" yeasts (present in the atmosphere) but the result will not be fit for human consumption.  (Experience from a small cooperative in Africa, where they pasteurized and concentrated orange juice for export :  any breakdown in the pasteurization line that took longer than an hour to repair would mean the juice going to waste.)

[Karen W.]

Now I had a pitcher of orange juice one of my children left in a cooler on the porch this had to have been over a month, I don't recall for sure but I think it was frozen from concentrate when I made it for them to take to the creek. they forgot the cooler with the juice and I forgot it was there also. now when I found the jug a child had set it back on the counter, I assumed it was new juice so i picked it up to put it away, and thought I think I will have a glass. It was in a Tupperware pitcher with water tight lid I went to open by pushing button down to relieve suction or seal.. and it blew off as I compressed the button sounded like a gun! scared the holey crud out of me! Then all I could smell was alcohol strong and pungent.. my daughter came in and said oh you found the juice.. I said did you put booze in this she said no it was in chest on porch... I told her well it ha...anyway I dumped it and it was strong!s fermented and is very alcohol like! LOL she came over and said ooh maybe I 'll keep it and make John drink it! LOL LOL

[Bored chemist]

Lots of things will grow on /in fruit juice. The commonest is yeast (of about a zillion different varieties) and produces alcohol and CO2 (which explains the bang).
Other microorganisms produce other by-products, some of these are really nasty poisons. The risk that these might infect the juice is fair grounds for throwing it away, particularly in a hot country. Personally, I might have found a tank for it and added some yeast. If the yeast gets going first then the alcohol it produces tends to suppress the growth of other bugs. The best things in life are free!
The acidity of some failed home brew is possibly due to acetic acid formed by a second bacterial strain metabolising the alcohol.

[Karen W.]

LOL..

Now I had a pitcher of orange juice one of my children left in a cooler on the porch this had to have been over a month, I don't recall for sure but I think it was frozen from concentrate when I made it for them to take to the creek. they forgot the cooler with the juice and I forgot it was there also. now when I found the jug a child had set it back on the counter, I assumed it was new juice so i picked it up to put it away, and thought I think I will have a glass. It was in a Tupperware pitcher with water tight lid I went to open by pushing button down to relieve suction or seal.. and it blew off as I compressed the button sounded like a gun! scared the holey crud out of me! Then all I could smell was alcohol strong and pungent.. my daughter came in and said oh you found the juice.. I said did you put booze in this she said no it was in chest on porch... I told her well it ha...does now,anyway I dumped it and it was strong! It fermented and was very alcohol like! LOL she came over and said ooh maybe I 'll keep it and make John drink it! LOL LOL