Lee's Multi differential Agar (LMDA) Medium

Lee's Multi-Differential Agar (LMDA) Medium is a complex nutrient medium that will detect most microorganisms commonly encountered in a brewery.

Beer is not a very appropriate medium for the development of bacteria due to its characteristics, such as the low quantity of available nutrients, the presence of alcohol, carbon dioxide and sulphur dioxide, as well as low conservation temperatures. However, growth of bacteria and wild yeast can contribute unwanted flavors to wort and beer. The degree to which it can affect flavor depends on the stage of brewing at which it occurs.

The main types of wort and beer spoilage bacteria include: Flavobacterium, Enterobacter, Escherichia, Lactobacillus, Pediococcus, Acetobacter, Acetomonas, and Zymomonas . Wild yeast strains come in two groups: Saccharomyces and Non-Saccharomyces. Both bacteria and wild yeast can cause turbidity, haze, slime formation, over-attenuation, souring, and off flavours in the product.

LMDA Medium is used for bacteria and yeast detection / enumeration. Colonies of acid producing bacteria will be easily identified by the development of a clear zone around them because of their ability to dissolve calcium carbonate present in LMDA medium. Furthermore, colonies identification will be facilitated by the characteristic color reactions. Bromocresol green turns yellow to indicate acid production.n Both ingredients work together to differentiate between true acid producers and slight acid producers. LMDA plates can be used aerobically or anaerobically depending on which bacteria the brewer wants to detect. Incubation is done under anaerobic conditions, except when acetic acid bacteria are of major interest, then aerobic incubation is used.

An antifungal such cycloheximide can be added to suppress culture yeast growth, therefore making this media selective to bacteria.