Maple syrup is a high value artisanal product produced mainly in Canada and a number of States primarily in the
northeast USA. Mold growth (Wallemia sebi) on commercial product was first reported in syrup in 1908. Since
then, few data have been published. We conducted a systematic examination for fungi in maple syrup from 68
producers from all of the syrup-producing areas of Ontario, Canada. The mean pH of the samples was pH 6.82,
sugar content averaged 68.0 ± 0.89 °Brix and aw averaged 0.841 ± 0.011. Some 23 species of fungi were isolated
based on morphology and molecular techniques. The most common fungus in the maple syrup samples
was Eurotium herbariorum, followed by Penicillium chrysogenum, Aspergillus penicillioides, Aspergillus restrictus,
Aspergillus versicolor and two species of Wallemia. Cladosporium cladosporioides was also common but only
recovered when fungi known from high sugar substrates were also present in the mold damaged sample. The
rarely reported yeast Citeromyces matrinsis was found in samples from three producers. There appear to be
three potential causes for mold damage observed. High aw was associated with about one third of the mold
damage. Independently, cold packing (bottling at ~25 °C) was a risk factor. However, syrup of good quality
and quite low aw values was contaminated. We hypothesize that sanitation in the bottling line and other aspects
of the bottling process may be partial explanations. Clarifying this requires further study.