Just made some sauce with a decent sized horseradish. Nice and smooth but very mild. Will it get stronger and how long will it keep? I did put a little oil and vinegar in.
http://horseradish.org/faqs.html
I used this recipe, putting it it a liquidiser (I didn't use the ice) and adding vinegar, and I have to say that an incautious sniff set my eyes and nostrils on fire. Then you can calm it down with creme fraiche or something.
I have Thai relations who are amused by our European wariness of what they call "spicy" foods, ie chilli used to the point of painfulness. I encouraged them, when visiting us, to try horseradish sauce and English mustard and they were absolutely horrified.