Once the alcoholic fermentation is over it is time to begin the Malolactic Fermentation (the next chapter will discuss the MLF in detail). Before MLF is possible, it's important to get rid of the unwanted solids left in the wine after pressing. A large amount of sediment will settle out of the wine in the first day or so after pressing. This layer is referred to as the lees. What drops out in the first 24 hours is called gross lees, there is nothing beneficial or helpful about them. In fact, the gross lees are often a source of harsh and bitter compounds that, if left in contact with the wine for an extended period of time, can develop negative sulfur flavors and aromas. In order to avoid potential problems, we suggest that you transfer the wine off of the gross lees between 1 to 2 days after pressing. After this transfer, the resulting wine is often quite clean and will have only a small quantity of light or fine lees (clean yeast, free of solids) that settle out to form a thin layer on the bottom of the vessel. Unlike the gross lees, the light lees are very beneficial to red wine at this stage and will serve as a nutrient source for the Malolactic Fermentation. Once off of the gross lees, the wine can safely work in a carboy, tank or barrels for the several weeks needed to complete the MLF. *Note: It is desirable for red wine to get exposure to oxygen during the first transfer, but only at the first racking. This serves to start rounding the flavors a little sooner. You can do this by simply lifting the transfer tubing up during the racking so that the wine runs down the side of the carboy or tank that you are transferring into. For all other subsequent transfers you will want to avoid the wine’s contact with air, and to leave the transfer tubing at the bottom of the vessel so it doesn’t splash while you are transferring.
This question has no right or wrong answer. Sur Lie aging as it's called (leaving the wine on the lees throughout the malo and aging) will result in a wine with increased body, decreased diacetyl from malo, and a more thoroughly integrated oak character. The lees do this for your wine through reactions based off of the degrading yeasts. Keep in mind, that you will need to stir the lees during the aging period. However, removing the lees following fermentation will result in a crisper, more fruit focused white. Either technique is valid depending upon the fruit in question and the desired style to be produced.
Pomace is the term given to the solids remaining after the juice/wine has been pressed from the must. It contains all of the skins, seeds, and stems that were present during fermentation.
The term "lees" refers to the substances that settle out following fermentation and pressing. In red winemaking the "gross lees" are compounds that settle within the 48 hours following pressing. These are generally negative substances that will contribute to astringency or instability in the wine. The "fine lees" are substances that settle following the gross lees, and they are a positive factor for the wine, as they act as a nutrient source for the malolactic bacteria.