Peel the roots and either slice or grate them. I use a food processor with the standard metal blade to grind the horseradish root, but you can use a blender, or a meat grinder. Whichever method you use, add a small amount of water, a tablespoon or so, depending on how much root you are processing, just to keep it moving around.
You can grate horseradish either by hand or with the processor’s grating blade, but again, use a bit of water. (If you are attempting to grate it on a box grater, beware!, the fumes are very potent!)
If it’s too runny, drain some water off, or too thick, add a bit more. Be careful. The fumes from the root can be potent! Fresh crushed horseradish is at its strongest, but once it is exposed to air, the pungency begins to wane.
Once you have a nicely ground texture, like the prepared horseradish you buy in the jars, you're ready for the next ingredient--vinegar. But read the next instruction carefully, don't just pour in the vinegar yet.
Use 2 to 3 tablespoons of (5% strength) white distilled vinegar and ½ teaspoon salt for each cup of grated root.
The key to making horseradish hot, and I mean HOT, is when to finish it off with the vinegar. Vinegar stabilizes the flavor, and the timing of when you add it will affect the spicy outcome. If you add the vinegar too soon, the horseradish will be milder in flavor. For “knock your socks off” spicy, be sure to wait three minutes before adding the vinegar.
So, to achieve the hottest horseradish, use the freshest root possible and be patient; wait three minutes before adding the vinegar and salt. Also, once your horseradish is complete, proper storage is crucial to maintain that heat. Store it in an airtight container in the fridge for four to six weeks or in the freezer for six months or even longer.