Question
I have one vine, probably of white wine grapes, though no one knows what variety. Not enough for wine, so I make jelly. How do I prevent the juice from oxidizing and turning brown? I put lemon juice into it, it didn’t help. (I.F.)
Answer
The browning is caused by an enzyme naturally found in grapes called ‘polyphenol oxidase’ that oxidizes phenolic compounds – also naturally present in the grapes. This reaction is slowed down by either refrigerating or freezing the product, lowering the pH (e.g. adding lemon juice as you did – but perhaps MUCH more!!) and/or by heating the product prior to bottling. I would suggest that you try one of these methods on a small quantity and when you perfect your method, apply it to your entire harvest. Let me know how it works out!
– Diane Barrett