Using processor fitted with shredder attachment, shred horseradish. Transfer horseradish to medium bowl. Fit processor with metal blade. Return horseradish to work bowl. Add next 3 ingredients. Process until almost smooth, scraping down sides of bowl occasionally, about 5 minutes. Mix in salt. Place horseradish in glass jar. Cover tightly; chill at least 1 day and up to 10 days.
