To use horseradish, peel the large, fleshy roots and cut into sections. Use a blender or food processor to chop the roots along with a small amount of water and a couple of ice cubes. Vinegar or lemon juice is added to stop the process that produces the “bite” of horseradish. Add immediately after blending for a mild flavor or wait up to 3 minutes to give the horseradish more kick. Use 2 to 3 tablespoons of vinegar or lemon juice per cup of horseradish sauce along with ½ teaspoon of salt for flavor.
Horseradish has an extremely strong odor and so you may wish to open the blender or food processor outdoors and to keep your face away from the container when opening. Store ground horseradish in a tightly sealed jar in a refrigerator until ready for use. (Ward Upham)