This is an old family recipe and is the best way to get a crazy spicy horseradish.
Most horseradish from the store has been pasteurized which will lose it’s heat, well, from heating it up. The ones that are HOT or Extra HOT usually have added seasonings (like white pepper) to add the heat back. That’s why freezing after making is the best way to preserve the heat and keep the horseradish fresh. These jars are not sealed and require refrigeration.