Horseradish is the big brother of all radishes-the root of a mustard family plant, it is not a radish at all. Hairy, brown to gray exterior, and a white interior, horseradish when grated brings tears to the eyes with its strong odor. The flavor is piquant and hot, and it is a favorite flavoring for sandwich spreads. The flavor is intense, and brings out the best in pickles and sauces.
To keep prepared horseradish (commercial or homemade) at its flavorful best, store it in a tightly covered jar in the refrigerator or in the freezer. It will keep its good quality for about four to six weeks in the refrigerator and for six months or longer in the freezer. Buy or prepare only the amount of horseradish that can be used in a reasonable time.

Fresh roots may be stored for several months if they are washed, placed in polyethylene bags, and stored at 32 to 38 degrees F. 

Horseradish is a perennial herb and a member of the mustard family, to which cauliflower and Brussels sprout belong. This pungent root grew in Greece more than 3,000 years ago. Medieval people regarded horseradish as an aphrodisiac and claimed it to be the cure for everything. From the Bible, it is known as one of the five "bitter herbs" and is traditionally served at Passover. Folklore also has it that the Indians used horseradish to treat toothaches. Horseradish syrup was taken as a cough medicine.

The plant was brought to the New World from England, but Germans, and Eastern Europeans had been complementing their meals with it long before the English.

The word "horseradish" first appeared in print in 1597 in John Gerard's English herbal on medicinal plants. A different view is that this herb was first called "harsh" radish because its volatile oils were bitter on the tongue. The word "horseradish" is believed to denote large size and coarseness, while "radish" comes from the Latin radix, meaning root.

Perhaps the first person to grind horseradish for profit was Henry J. Heinz (Oct. 11, 1844), the founder of the mammoth H. J. Heinz Company. As a small boy, Heinz helped his father grind the root in the basement of their home. It wasn't until the fall of 1933 that studies were initiated by the Illinois Agricultural Department. The most recent discovery came at M.I.T., where scientists say that the enzyme "horseradish Peroxidase" removes a number of pollutants from waste water -- another testimonial to the potency of this surprisingly delicious root! For more on this wonderful root member of the mustard family follow this link:
http://foodwine.com/food/egg/egg1296/horscap.html