According to Harvest to Table, there are several things to look for when buying fresh horseradish. The primary thing is to make sure the root doesn’t have soft spots or a spongy feel. There are also some visual cues that will indicate that it’s a less-than-optimal root, so avoid any horseradish that has visible mold, blemish spots, fresh sprouts growing out of it, or ones that have a fresh green rather than coarse brown outer skin.
The site also recommends not cutting the root before you’re ready to use it, and the same applies when purchasing it. The ends of the root should look as though they’ve recently been cut, so that you’ve got the longest possible period of freshness. Lacademie further explains that you should not purchase any root that shows signs of wrinkling or has excessively dried-out portions. The next time you’re at the supermarket when horseradish is in season, look for a root with these things in mind to ensure the horseradish you’re grating is at its peak freshness and flavor.