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Microbe Guide: Fusarium domesticum

Washed rind cheeses are hostile places for most molds. The continuous washing of the surfaces of these cheeses breaks up the networks of molds (mycelium) and generally favors the growth of yeasts and bacteria. But one mold, Fusarium domesticum, has figured out how to cope with this highly disturbed cheese environment. In addition to being a survivor in its own right,  Fusarium domesticum offers some saving graces for cheese makers looking to stabilize the integrity of their rinds.

 

Macroscopic appearance:
In the lab growing on standard plate count agar, Fusarium colonies are tan and somewhat oily in appearance. They form dense mounds that are generally quite flat, but can be raised in the center. Growth is moderate: slower than Penicillium species, but much faster than slow-growing molds such as Sporendonema or Chrysosporium.

Colonies of Fusarium domesticum growing on plate count agar in the lab (left). Characteristic white frostiness of the same mold growing on a washed rind cheese aged by the Cellars at Jasper Hill.

Colonies of Fusarium domesticum growing on plate count agar in the lab (left). Characteristic white frostiness of the same mold growing on a washed rind cheese aged by the Cellars at Jasper Hill.

The appearance of this fungus on cheese is completely different from that in the lab. When it grows on the surface of the cheese it produces a dense and short white frostiness that sometimes has hues of pink in it. When left to grow without washing, it will form a dense white coating on the cheese surface. When washed continuously (at least once a week) will with remain patchy and frosty in appearance.

Food habitat:
This fungus is a huge fan of washed rind cheeses. Because most other molds are wiped out from the disturbance of washing the surface, Fusarium can flourish in this open niche. Fusarium is often inoculated onto cheeses as a starter culture, but I’ve isolated this fungus from raw milk cheeses where starter cultures have never been used. Where outside of the dairy environment this fungus originates is still unclear.

This fungus can grow at high acidity, so it is able to colonize the surface of relative fresh cheeses. It also has a pretty good salt tolerance, being able to survive the high salt (usually ~20%) brines used to wash cheese surfaces.

Impacts/Functions:
Because of the high moisture and stickiness of washed rind cheeses, their rinds can often fall apart as the cheeses are manipulated during the aging process.  When the Swiss originally described Fusarium domesticum, they noted that the cheeses where it was most abundant also had superior rind stability. The exact mechanism for promoting rind stability is unknown, but it could be from the mycelium of this fungus crossing the layer between the sticky rind and the more firm paste of the cheese curd.

As I describe on another page, this fungus can also contribute to rusty-orange color formation of cheese rinds. The specific compounds that create these pigments haven’t been identified in Fusarium domesticum, but other Fusarium species have been shown to produce carotenoids, which are often orange in color.

The contributions of Fusarium domesticum to cheese flavor are unclear to me. In the lab, I think this fungus smells like cat urine. I’d love to hear from anyone (use the comment section below!) that thinks they can attribute a particular aroma or flavor contribution to this fungus.

For more details on Fusarium domesticum, check out the following papers:
Bachmann, H. P., et al. “Occurrence and significance of Fusarium domesticum alias Anticollanti on smear-ripened cheeses.” LWT-Food Science and Technology 38 (2005): 399-407. http://www.sciencedirect.com/science/article/pii/S002364380400163X

Ropars, Jeanne, et al. “A taxonomic and ecological overview of cheese fungi.”International journal of food microbiology 155 (2012): 199-210. http://www.sciencedirect.com/science/article/pii/S0168160512000852

 

Post written by Benjamin Wolfe. Header photo by Benjamin Wolfe.

 

 

 

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