IDENTIFICATION OF LAMBIC SUPERATTENUATING MICROORGANISMS BY THE USE OF SELECTIVE ANTIBIOTICS

The microbial population present in lambic beer after one year of spontaneous fermentation consists mainly of Brettanomyces yeasts, lactic acid bacteria and acetic acid bacteria. The density of the wort by that time has decreased to around 3.5-degrees Plato. At that time a period of superattentuation is initiated, resulting in a lambic with sometimes less than 1-degrees Plato. Such old lambics are used in the production of gueuze. In order to find out which organisms are really necessary for this process, lambic attenuated to around 3.5-degrees Plato was pasteurized and re-inoculated with a mixed microbial population obtained from fermenting lambic. By the addition of the antibiotics actidione, pimaricin, gentamycin, oxytetracycline and nisin it was found that Brettanomyces was the main organism responsible for superattenuation, although this was less pronounced when Pedicoccus was absent. Acetic acid bacteria were not involved. Bacteria alone were not really superattenuating. The process with lambic wort which had reached the 3.5-degrees Plato value by a natural spontaneous fermentation was slower than with a lambic wort pre-fermented to 3.5-degrees Plato with S. cerevisiae. It was found that Brettanomyces but not Saccharomyces survives well under the conditions normally found for a 1 year old lambic.