The four major contaminant species were compared for biofilm
formation and ethanol inhibition (Fig. 4). Isolates of L. casei were
predominantly non-biofilm forming and not inhibitory to ethanol
production (Fig. 4A). Only 8% of L. casei isolates formed biofilms,
and 15% of isolates reduced ethanol yields by more than 10 g
ethanol/L, with none reducing yields by more than 20 g
ethanol/L. By contrast, 82% of L. fermentum isolates reduced
ethanol yields by more than 10 g ethanol/L, with 43% reducing
yields by more than 20 g ethanol/L (Fig. 4B). However, only 12%
of L. fermentum isolates were strong biofilm formers. Similarly,
67% of L. mucosae strains inhibited ethanol production by more
than 10 g ethanol/L, with 33% inhibiting production by more than
20 g ethanol/L (Fig. 4C). Only 16% of L. mucosae were strong biofilm
formers. L. plantarum strains were least inhibitory to ethanol
production, with only a few strains being strongly inhibitory
(Fig. 4D). Only 13% of L. plantarum strains formed biofilms, and
none of these were inhibitory to ethanol production. Overall, no
correlation was found between biofilm formation and ethanol inhibition
among the four major contaminant species. L. mucosae and
particularly L. fermentum exhibited the greatest potential to cause
stuck fermentations. On the other hand, the most abundant species,
L. plantarum, had few isolates capable of causing stuck