A few drops of lemon juice added to cream before whipping can prolong the life of the whipped cream.
We’ve come across this theory before and so decided to test it by adding 5 drops of lemon juice—about 1/16 teaspoon, the usual amount suggested—to 1 cup of heavy cream before whipping it. The cream whipped up nicely to stiff peaks that stood up to those in a bowl of cream whipped without lemon juice. In fact, the lemon juice may have added stiffness and body to the cream by coagulating some of its protein (casein) to form solid curds. The citric acid in lemon juice is surprisingly strong, and even at 5 drops of juice per cup, the acidity (according to the food scientist we spoke with) is more than enough to coagulate casein.
But the lemon-whipped cream didn’t stand the test of time. If anything, it deteriorated more quickly. In this and past tests we’ve found that heavy cream will maintain its whip for about 24 hours. At 24 hours, the cream with lemon juice showed more seepage of liquid. This can be attributed to the fact that proteins have a stabilizing effect on foams by reinforcing the walls around the pockets of trapped air. Because the lemon-treated cream contained less free protein, it broke down more quickly than the cream without lemon juice.