Bacteria, lactic acid oxygen effects

Effect of Oxygen on Metabolism of Lactic Acid Bacteria... 

It has been claimed that the lethal rate is enhanced when carbonated instead of noncarbonated beer is used. The most resistant of the normal brewery contaminants are members of the lactic acid bacteria and certain species of Saccharomyces, e.g. S. pastorianus. Special difficulties attend the pasteurization of returned beer where the level of contaminants may be very high. However since such beer may be filtered before pasteurization and is usually blended into conditioning tank at low rates, the adverse effect on flavour of using a large number of pasteurization units may be discounted. With normal beers, excessive pasteurization leads to cooked, biscuity flavours, especially when the dissolved oxygen content of the beer is high (say in excess of 0-3 mg/1). 

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