“ The rind, from
an ecological
perspective,
is particularly
fascinating”
produce the grey-green mould used to
make many cheeses, such as the Golot
cheese of Turkey, and again in around
1900 to produce the characteristic white
mould used in Camembert.
In the cheese ecosystem, moulds can
work with other organisms to form particular
flavours and textures. In Stilton, for example,
P. roqueforti teams up with a yeast called
Yarrowia lipolytica, known for its ability to
break down lipids and proteins. This boosts
the number of ketone aroma compounds,
characteristic of smelly blue cheeses.
Gene-swapping orgies
The cheese on your plate is a den of gene-
thievery. In the thousands of years since
cheeses were first created, the microbes
that make them have been rampantly
swapping genes as they evolved to
survive in this new environment.
One study by Wolfe and his colleagues of the
genomes of 165 species of bacteria associated
with cheese found that 80 per cent of them had
acquired genes directly from others through a
process called horizontal gene transfer. Many
of these genes were involved with scavenging
iron, a rare commodity in cheese. “Iron is
incredibly limiting in this environment,”
says Wolfe. “The winners are really those
that have the ability to quickly find the iron.”Warfare
It is a battle for survival in cheese, which means
organisms need some weapons up their sleeves.
A 2020 analysis by Cotter and his colleagues of
the microbiomes of 55 artisanal Irish cheeses
revealed that around 20 per cent of microbes
in those cheeses contain genes for compounds
called bacteriocins that kill their rivals. This is
far higher than the 13 per cent found in our gut,
for example, as well as other environments.
“We were a bit surprised,” says Cotter.
Another inside-the-rind evolutionary
arms race involves bacteria and viruses. About
20 per cent of the organisms living in cheese
are bacteriophages, viruses that infect bacteria.
But Cotter and his colleagues’ study showed that
bacteria are armed with a defence mechanismcalled CRISPR to destroy bacteriophages, while
the viruses are equipped with anti-CRISPR
proteins to dodge these attacks.
The top dogs of the cheese microbiome
are fungi. “In these communities where you
have both fungi and bacteria living together,
the fungi really seem to be the drivers of
the interactions,” says Wolfe. “We’ve seen
examples where the fungi are wiping out
the bacteria through the production of
antimicrobial compounds.”
But fungi don’t always win. On the rinds
of certain cheeses, such as Milbenkäse,
produced in Germany since the Middle Ages,
fungi are preyed on by cheese mites.The bit you throw away
The rind, from an ecological perspective,
is particularly fascinating. It acts not only as
a barrier, but as a controller for the microbial
action within. “As the rind grows, it releases
enzymes that break down the milk and
produce a lot of the flavours that we enjoy,”
says Wolfe.
In Camembert, for example, the
characteristic surface mould P. camemberti
produces ammonia, a key cheese flavour
molecule. This diffuses into the centre,
increasing the pH and ripening the cheese
by degrading the milk protein casein.
But the big question is: should we eat
the rind? The answer depends on what kind
of rind it is, and there are three main types.
You have the fuzzy white ones found
on cheese such as Brie, and the sticky,
pungent ones found on cheeses that have
been washed in brine, wine or beer, such
as Gruyère. These might taste “funky”, says
Wolfe, “but you can eat them for sure”.
The third type is known as natural rind. You
might find this on blue cheeses or cloth-bound
Cheddars, resembling lichen growing on the
surface.“That’s more of a functional rind, to
help control moisture loss and prevent bad
microbes from growing on the surface and is
not there for flavour,” says Wolfe. “It’s totally
fine to it eat it, but I tend to cut it off. ❚Alison George
is feeling gouda18/25 December 2021 | New Scientist | 61