Apart from the tender loving care, what we did was:
1. Put the casks out in the sun during the day, and back in the bodega at night.
2. Mix in about 1 liter of our Airén which was in fermentation and so full of active natural yeasts
I can't believe there no word in English for a "punching down tool"!!! I've looked (rather hurriedly) but couldn't find anything better!