First, the pre-cooking is needed in order to peel them effectively and to eliminate any of the peel contaminants from being transferred to the beet itself as would happen with manual peeling.

Second, if peeled first then all the color washes out of them. That is why leaving a 1" portion of the stem attached is recommended - to prevent wash out.

Third, it makes them softer, more tender, more palatable rather than rock hard.

But the primary reason is to insure they are heated all the way through before pickling them. It not only kills internal bacteria but begins the weakening of the cell walls so that the pickling brine can penetrate.

The pre-cooking time needed varies by the size and variety. In some cases it may only take 10-15 mins. until they are fork tender. For extremely large ones that are woody it may take an hour or more. So sorting by size really helps and frequent check for fork tender will determine the cooking time needed.

Dave