The chemistry of brewing and of beer 351 by higher temperatures and light levels and th presence of metal ions The relationship between oxygen content of beer and formation of staling may readily be Beer high content significantly higher levels of carbonyls after storage, including as-2-nonenal, octanal, iso-butenal and 2-phe- nylacetaldehyde, although levels of trans-2-trans and In beer of very high oxygen content, trans-2-nonenal is further d&raded to other flavour active compounds of unknown nature Although a degree of protection is obtained by minimizing the content of beer a high level of oxidation the final beer. oxidation during wort production, for example the concentration of reducing compounds and the reduce tive capacity of polyphenols, etc. There is an obvious relationship between the development of and good brewery practice Turbrd worts, for ex a deficient lauter system have a high level of long chain fatty acids nyls prepared from turbid wort may contain high levels of carbo such as trans-2-butenol, iso-butanal, trans-2-nonenal, iso valeral and 2.phenylacetaldehyde shortly after manulacttire. Simi larly the amino acid level content of wort, should be as low as carbonyls "through, ze the formation of proline whichhas Strecker degradation and other reactions. sent in nificant quantities in er, is of portance in promoting the aldol condensation of a hydes products in flavour deterioration of beer is The role of M Sometimes ov leads directly to flavour defect include a dicarbonyls which react with amino acids in t d in ed beer also reduce flavour the extent of the Maillard reaction i more important in determining levels of some carbonyls (trans-2 trans-4-decadienal trans-2-trans-A-undecadienal than content