|Horseradish (flowering plant)|
The pungent allyl isothiocyanate is not heat resistant; therefore, horseradish is only seldom used for warm foods and then added immediately before serving. Even in cold water, allyl isothiocyanate is not stable for longer than a few minutes. However, in sour environment the hydrolysis of thiocyanates takes place much more slowly.
In Austria, freshly grated horseradish (or tinned product) is frequently mixed with grated apples (sour varieties preferred, otherwise some lemon juice is needed) and then eaten as a spicy relish to fried or cooked meat. This mixture (Apfelkren) can be stored for about one day without substantial loss in pungency. To prevent darkening of the apples (enzymatic oxidation of phenolic compounds by oxygen), the apples may shortly steamed before mashing them; this won’t much affect the flavour but gives a softer, smoother texture.
For a comparison of different pungent spices, see negro pepper.