What do you add to whipping cream keep it stiff?

To keep whipping cream stiff, you can add a small amount of cream of tartar or lemon juice. Cream of tartar is an acidic powder that helps to stabilize the proteins in the cream, while lemon juice contains citric acid which has a similar effect. Adding either of these ingredients will help to prevent the cream from becoming runny or separating. You can also chill the whipping cream and your mixing bowl before you start whipping it, as this will help the cream to whip up more quickly and hold its shape better.