We grow a fair bit of horseradish. It is planted in a raised bed as it can be a bit of a monster if it is not contained. It is a fabulous high yielder that takes minimal care and provides all year in our climate once established. Tolerating hot summers and cold frosty winters. At $65/kg in the shops it is much better to grow it yourself. We use the young leaves for salads and stir fry and keep the grated root in the fridge for meat and fish.
The root looks a bit like the mandrake root from Pans Labyrinth and it will come to life if left under the bed in a bowel of milk.
Cleaned and washed
It is a bit deadly when it is grated and so it is best to do it outside and by hand. Grating in a processor seems to release more of the oils so watch out. Either way there will be tears.
Once grated put in a jar, cover in vinegar and keep in the fridge. It will go brown when past its use by date. It can be sprinkled as is on meat and fish or mixed with creme fraiche and a bit of salt for horseradish cream.
A little goes a long way and perhaps the best way to store horseradish is to leave it in the ground until you need it.