c) Non-biological haze formation roblem in brewin Haze formation auring storage of finished beer also occurs, in asso an increased affinity of proanthocyanidins for protein. The reason a for this is not fully understood, but earlier theories involving the oxidative polymerization of proanthocyanidins are being super ed by the concept of difea or indirect hydroxyl radical attack cing proanthocyanidin oxidation products with a large ity for proteins. 7.5 MICROBIOLOGICAL PROBLEMs AssoCIATED WTTH BEER Microbiological problems associated with beer are almost entirely of off taints and visible Spolrige growth of non or in the culture micro-organisms, during the brewing process ements in the general standard of hygiene and in the construction and d equipment, together with wide spread application of r pasteurization and sterile filtra tion have reduced spoilage problems in recent years for spoilage, however, always exists and it must be emphasized that and indirect, can be sufficiently serious to threaten the survival of smaller brewery companies 7.5.1 Beer as an environment for micro-organisms is poor and this is reflec ted in the fumber of micro-organisms abr to potential, rela in e. low pH value, low redox tively low nutrient level, presence of ethanol and other metabolites control microbial growth and must be tolerated, in combination, by any micro-organisms devel oping in beer. In some cases tolerance of the stress factors reflects a general characteristic of the type of micro-organism, but in others