ANSWER: Sustainable farming is a widely used term but has no legal definition - so it can mean just about anything. It's typically used by wineries that are just beginning to embrace concepts that protect and perpetuate the land, rather than stripping it.

Organic farming feeds the plants without the use of synthetic insecticides, fungicides and fertilizers.

Biodynamic farming feeds the soil, keeping it alive and healthy through the use of organic materials. It also uses Earth's natural cycles and preparations to produce balance in the soil and plants.

To put it another way, organic farming is concerned primarily with substances, whereas Biodynamics is concerned with forces.

TOMORROW: A look at the Biodynamic farming at Napa Valley's Grgich Hills Estate.