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Foaming can be a troublesome by-product of an aerobic bioreactor treating wine cellar effluent.  The foaming is caused by the composition of wine and cleaning chemicals used in the cellar. PROTEIN FOAMING Next time you drink wine, red or white, with a straw experiment abit by blowing into the wine.  A wonderful froth bubbles almost immediately.  This nameless property of wine is partly due to the presence of proteins. Proteins have been used for many years as whipping agents in meringues, marshmallows, and nougats. Egg white (albumen) was the original ingredient used in these products, and it is still used in large quantities by the food industry. Other whipping proteins include casein and soy-based proteins.

Natural foaming in mountain waters.

Foams are formed when globular proteins (which are globular because of the strong intermolecular associations between their animo acid residues) are opened up and reformed into protein "skins" that hold air bubbles in place. Proteins are typically present in wines in low concentrations, contributing little to their nutritive value. However, they assume a considerable technological and economical importance because they greatly affect the clarity and stability of wines. Although exhibiting a large diversity, the majority of the wine proteins are structurally related and have been identified as pathogenesis related (PR) proteins. Thus, different wines are essentially composed by identical sets of polypeptides. They derive from the grape pulp, and survive the vinification process simply because they are highly resistant to proteolysis and to the low pH characteristic of wines. There is increasing evidence suggesting that although protein-dependent, the development of turbidity in wines is controlled by a number of factors of non-protein origin, such as polyphenols, the wine pH and the presence of polysaccharides. A variety of procedures has been developed and tested for the specific removal of proteins from wines. Even though bentonite fining is nonspecific and can impair the quality of wine, it remains the only effective method to stabilize wines. CHEMICAL FOAMING

Foaming in a bioreactor caused by cleaning chemicals in the waste water

Cleaning chemicals usually foam when agitated vigorously.   Manufacturers of cleaning chemicals encourage foaming properties for the following reasons;
  • The visual effect of foaming gives a quick indication of areas being cleaned
  • Wetting agents, added to cleaning chemicals readily foam when agitated.  It is a tricky and expensive procedure to produce a cleaning chemical that does not foam
In the picture to the right, some expansive foaming is clearly visible above this open roofed bioreactor.  The foaming offers a quick indication of excessive and wasteful chemical usage. HWT wine cellar bioreactors usually have a covering roof to contain the foam.  Not only is foam a nuisance, but it also lifts biomass and quite quickly all the biomass can be lying around the bioreactor rather than inside.  The attendant mess and drastic dip in effluent quality are compelling reasons to keep a wine effluent bioreactor well covered.