I just found the Home Brew Forums, and am thrilled to be joining in the conversation. I've been making cheese at home for about two months now - having a blast!
I made a Horseradish Cheddar over the weekend. I used Ricki Carroll's Stirred-Curd Cheddar Recipe as the foundation of the recipe.
I actually wanted to do a Horseradish Cheddar and a Jalapeno Cheddar (separately), so after cooking the curds (step 9), I divided them into two roughly-equal parts.
To one half I added two tablespoons of Gold's Prepared Horseradish. It was the "purest" prepared horseradish I could find--only contained horseradish, vinegar, salt, and "flavoring". Most of the prepared horseradishes I found contained eggs, sugar, and preservatives. Yuck!. (Key: Look for the horseradish in the refrigerated section, not in the shelved condiments aisle.)
To the other half I added two tablespoons of chopped jalapenos (from a jar of jalapeno slices in vinegar/salt that I already had in my fridge).
I realized that the two would blend a bit too much in the press, so I first pressed one for a little bit, and then the other... And then kept them separated in the press by wrapping them individually in cheese cloth. Seemed to work okay, but only time will tell.
As to the quantity of horseradish, I used two tablespoons for one pound of cheese. So if I were making the full two-pound recipe it would have been four tablspoons.
It definitely smells strong (but not too strong, I hope), but it's hard to tell. I really won't know until after it's aged... I'm not sure if the flavor will get weaker, stronger, or stay about the same. I'll report back in two months!
Also, tomhog's suggestion about straining into the milk at the start of the process sounds like a good idea. I would have done that if I wasn't splitting up the batch.
I also considered using fresh horseradish. My plan for that was to get a piece of fresh horseradish root (My local whole foods didn't have any, shockingly!), and then grate it into water, boiling the water... basically following Ricki's Japaleno Cheddar recipe but with horseradish instead... So if anyone tries that, please let me know how it turns out!
I've described it a bit more on my blog, and have included a few photos, too....
Hope that's helpful!