Cut fruit turns brown when oxygen reacts with enzymes in the fruit. Choosing ripe fruit without bruises prevents some browning, but not all. The discolored fruit isn't dangerous to eat, but it is unattractive. You can slow down the browning with an acidic solution, allowing you to cut fruit ahead of serving time.
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A Touch of Lemon
The acid in lemon juice slows down the enzyme activity that causes your apples, peaches, bananas and other low-acid fruits to brown. Stir 3 tablespoons of the lemon juice into each quart of water. As you peel and cut each piece of fruit, immediately plunge it into the lemon juice mixture. Soak the fruit for up to 20 minutes and then rinse it with clear water. Keep in mind that the lemon juice solution can add a bit of citrus tang to the fruit.
Salt and Vinegar Solutions
If lemon juice isn't available, you can substitute vinegar or salt. These anti-browning ingredients affect the flavor, so they're better reserved for fruit to be used in baking or preserves -- the sugar or syrup masks the flavor changes. Use 2 tablespoons of salt or vinegar for every gallon of water. Soak the cut fruit in the solution for up to 20 minutes, and then rinse it well before using it.
Take Your Vitamins
Vitamin C tablets contain enough citric acid to stop fruit from browning. Crush 500 mg tablets into a powder, and then mix in 3 crushed tablets per quart of water. You can substitute 1 tablespoon per gallon of water of pure citric acid for the vitamin C. Soak the cut fruits in the solution for at least 10 minutes. There's no need to rinse, because tablets and citric acid don't alter the flavor of the fruit.
You can buy ascorbic acid where canning supplies are sold. Mix up to 1 tablespoon of the acid for every gallon of water in a bowl, and treat the fruit as you would with vitamin C or citric acid. This is another option if you don't want your anti-browning solution to affect the flavor of the fruit.
Overripe fruit typically browns more quickly, so eat the fruit before it passes peak ripeness. Cold water also slows browning, so use it in whichever anti-browning recipe you choose to follow. Store the fruit in a sealed container in the refrigerator if you aren't going to serve it immediately after cutting and treating it.