Only few researchers have published work on grape pomace, which today is a very significant waste product in agriculture industries. Grape pomace is the residue left af­terjuice extraction by pressing grapes in the wine industry. Globally, about 10 million tons of grape pomace (seeds, skin, and stem) is produced each year. In Spain alone, over 250 million kg of this by-product are used every year either as animal feed (with low nutritional value) or for ethanol production by fermentation and distillation (low level benefit). This material is underexploited and most of it is generally disposed in open areas, leading to serious environmental problems [77]. Israilides et al. [46] ex­tracted the sugars in the grape pulp by using hot water at 65-70 °C and then clarified the solution and used for pullulan production by A. pullulans NRRLY-6220 cultures. Since the grape pomace extract mainly contained sugars and very low amounts of protein, the polymer produced was very similar in its amount as well as molecular weight to the pullulan produced in defined medium. Moreover, the pullulan yields were high reaching 22.3 g/L after 7 days of fermentation period. Stredansky and Conti [53] tested grape pomace, tangerine peels, and apple pomace as substrate for xanthan production by solid state fermentation (SSF) with X. campestris NRRL B — 1459 cultures. These substrates were soaked in alkaline solution to neutralize the organic acids and then added to the fermentation media. Performances of these feed­stocks were also evaluated in the presence and absence of spent malt grains as inert support and apple pomace proved to be a superior substrate yielding high amounts of xanthan under both conditions. Low xanthan yields with grape pomace were at­tributed to the low sugar content used and the low absorption capacity of the solid material.