How does preservative affect brew?

[simple one]

Having done only country wines and beer, i am amazed by the use of cartons of drink to brew! I was always under the impression that the preservatives in the cartons stopped the yeast fermentation? Is this not true, or do you have to boil it out, or over pitch the yeast?

cheers matt.

[edit1now]

Most long-life fruit juices are heat-treated like UHT milk so they're effectively sterile, so the manufacturers don't have to add preservatives as well. Non-long-life items like concentrated Ribena will contain preservatives like potassium sorbate because the bottle of potential growth medium has to last both on the shelves and once opened in the customer's kitchen.

So... yeast grows happily in long-life juice, and less well in something made from bottled juice drink concentrate (yes, I know all cheap fruit juice says "made from concentrate" but that's a syrup like liquid malt extract, concentrated and frozen to make it smaller and cheaper to get from South America to the UK, not a "concentrated fruit juice drink").

[simple one]

Wow, why does anyone buy booze? So another question, what sugary drinks just will not ferment?

[edit1now]

I think I read that pineapple juice might not ferment because of some enxyme it contains, but somebody here will probably correct me...

[fatbloke]

I think I read that pineapple juice might not ferment because of some enzyme it contains, but somebody here will probably correct me...

Dunno about that, I know that it can be fermented but some combinations of juices when mixed with pineapple can make some strange tasting mixes.

Or it's also feasible that you could get problems like making "hot mixed" rhubarb, where you can get some "jellification" issues. Personally the only preservative that's acceptable is "ascorbic acid" a.k.a. vitamin C. Any of the "proper" preservatives need to be driven off with heat and then you'd need to hit the must with plenty of pectolase before fermenting it!