Spicy Horseradish Tips

If purchasing horseradish, look for firm, unblemished roots. When cut, the root should be creamy white.
The root can be stored for several months between 32-38 degrees F. (0-3 C.), but for the hottest horseradish sauce, use as soon as possible. The heat begins to fade the longer it is stored.
Similarly, if you have horseradish sauce or cream that isn’t hot, the likely reason is that it has been sitting around for too long or it was made incorrectly. The sauce itself should be creamy white and will darken and lose potency as it ages.

To prepare your own horseradish

1 c grated horseradish root
2 - 3 Tbsp distilled white vinegar
1/2 tsp salt
Directions
Work either outside or in a well-ventilated room.
Peel the roots and either slice or grate them. Sliced root can be ground in a food processor, blender, or meat grinder with a small amount of water.
You can grate horseradish either by hand or with the processor’s grating blade with a bit of water. If it’s too runny, drain some water off; or too thick, add a bit more. Be careful. The fumes from the root can be potent! Fresh crushed horseradish is at its strongest but once it is exposed to air, the pungency begins to wane.
The key to making horseradish hot, and I mean HOT, people, is when to finish it off with the next ingredient — vinegar. Vinegar stabilizes the flavor and when you add it, will affect the spicy outcome. If you add the vinegar too soon, the horseradish will be milder in flavor.
For “knock your socks off” spicy, be sure to wait three minutes before adding 2 to 3 tablespoons of (5% strength) white distilled vinegar and ½ teaspoon salt for each cup of grated root.
So, to achieve the hottest horseradish, use the freshest root possible and be patient; wait three minutes before adding the vinegar and salt. Also, once your horseradish is complete, proper storage is crucial to maintain that heat.
Store it in an airtight container in the fridge for four to six weeks or in the freezer for six months or even longer

Read more at Gardening Know How: How To Make Horseradish Hot: Why Is My Horseradish Not Hot http://www.gardeningknowhow.com/edible/herbs/horseradish/make-horseradish-hot.htm