10/06/2026
A rough diagram of what's happening in your fermenter, for educational purposes. This was taken just after a punch down.
Yellow: This is "gross lees" (gross because it's a bit nasty), this is made of yeast cells from ferment; dust, dirt, other organic matter, and debris that's was on the grapes during the time of harvest. It settles to the bottom of the tank.
Red: This is the w**e, which still has suspended yeast cells, metabolizing sugars to alcohol under anerobic conditions. There's lots of CO2 in this, a by-product of fermentation.
*Red Arrow signifies that the area of the w**e will increase as ferment continues, until the next punch down*
Blue: This is what's known as the cap. This is comprised mostly of seeds, skins, and stems that are made buoyant by CO2. Left undisturbed, this compacts at the surface forming something like a crust on top of the vat. Once ferment completes, the cap will sink to the bottom.
The reason a w**ery "punches down," "pumps over," or "boils over" their vats is to make sure they extend the contact time of the w**e on the skins, seeds, and stems, maximizing extraction of flavor compounds.
**ery **e **emaking
