Question:
How can I lock in the brilliant color of purple grapes when making sorbet? I pulverized grapes in a blender and strained through a chinois, but the color became dull. In the next batch I added fresh lemon juice. The color still faded.
– Adrienne Hall, Chef, Drexel University, Philadelphia, PA
Answer:
As you know from winemaking, the color of red grapes comes from the skins. If you squeeze a fresh red grape, you will notice that the juice that comes out is clear or nearly clear. If the juice’s contact with the skins is minimized, winemakers can even make white wines from red grapes such as blanc de noirs Champagne.
Getting the beautiful color of the red grapes into your dessert is also all about the skins. Food processors often use previously frozen grapes (same for other fruits like cranberries) because freezing disrupts the cellular structure of the fruit and allows the color to bleed a bit. Pureeing is a good idea, as is letting your puree sit in the refrigerator for a few days before using it, so the juice infuses with more color from the skin. And you’re on the right track with the lemon juice—acidity helps brighten the color of red pigments.
Will Goldfarb, a pastry chef and founder of Willequipped and Willpowder says, “Part of the fading is due to the aeration. Churning will by nature ‘whiten’ the color as it whips and freezes. Perhaps a straight granita would have the purest color.” To get the most brilliant possible color from the grapes, Goldfarb suggests using a wine press (it makes sense—if winemakers get great color using a press, why not cooks?) and suggests that powdered citric acid may be more effective than lemon juice.
Let us know how it goes!