Wash the horseradish roots very thoroughly and peel them using a vegetable peeler and removing all the brown spots.

Quickly rinse the peeled horseradish again to remove any lingering dirt. Dry well.

Either grate it by hand (small shredder side of a box grater) in a well-ventilated room or cut it into chunks and process it for a few seconds in the food processor.

Mix it with salt and vinegar. Don't add too much vinegar, the mixture should be wet but not sopping wet. If you add the vinegar immediately after grating the horseradish, the final product will be milder. If you wait for a few minutes before adding the vinegar, the preserved horseradish will be stronger.

Stuff the horseradish into small jars, pushing it down with a small wooden rolling pin or something similar. If the mixture seems to be too dry on top, pour a few more drops of vinegar in the jars.

Screw the lids of the jars on top and seal them with some sticking plaster for good measure. Keep refrigerated.