Volume 16, Issue 5: Summa Cum Biologia
This will not be the musings or rather, random
neuron firings of a gifted writer. Rather, it will be an actual
attempt at data transfer of true phenomena from the real,
empirical world of food microbiology from a marginal writer who
hopes he may have some potential for the craft (being
genetically related to two writers within these shiny pages).
For those of you who are cheese-o-philes you can
thank God for creating the various and sundry species of
bacteria and sometimes fungi essential to its formation. We are
all usually revolted when milk goes sour, but often some of
our greatest blessings are the result of harnessing certain
critterswhich if left alone often produce putrid
thingsand putting them to good use. Cheese production is just
one example. I will try to simplify things, so don't be too
offended if I insult your intelligence.
Milk has a particular protein called casein (pronounced
case-seen). When it begins to sour, it is because certain species of
Streptococcus (or other bacterial species) are living off of
the milk sugars (lactose). One of their metabolic waste products is lactic
acid (or other acids from other bacteria) which they excrete. This causes the pH to drop below
neutral (acidic) and the casein protein can no longer remain
dissolved in solution. When this happens, the proteins are said
to precipitatethey settle at the bottom of the liquid as a solid.
When casein precipitates en masse, we say that the
milk is curdling. Rennin is an enzyme which is used in the
cheese industry that speeds up the curdling process. Do you want
to know where we get rennin? You do? Goodfrom the
lining of a calf's stomach.
When milk has been properly curdled, we basically
have unripened cheese. At this point, it can be
commercially marketed as cottage cheese. But if ripened cheese is the
goal, the curds are washed, pressed (to squeeze out the
whey), sometimes cooked, and then sliced up into the
appropriate shape. Many times the curds are salted to the desired
taste and allowed to ripen (bacterial fermentation) for a
particular length of time, at a particularly warm temperature and
high humidity. Salting obviously adds flavor, but it also
controls moisture and prevents the unwanted growth of other
You may have wondered about the curious cavities
in Swiss cheese. In short, two species of bacteria are
grown within the curdling milk.
Lactobacillus is used to produce the aforementioned lactic acid which curdles the casein.
Another bacterial species called Propionibacterium
produces propionic acid and carbon dioxide as metabolic waste products.
The latter, being a gas, accumulates in nooks and crannies
between the curds and exerts enough pressure on the
surrounding cheese to form CO2 bubbles that remain trapped in
the stiffening cheese. These trapped bubbles are referred to
as eyes or holes.
Both cheddar cheese and Swiss cheese are
internally ripened by fermenting bacteria. However, many
cheeses require more microbial action than just internal bacteria.
Certain fungi have earned a right to grow in and
on certain cheeses because of the peculiar flavor they bring to
the palate. Two species of mold, Penicillium
roquefortii and Penicillium camemberti,
are purposely added to produce Roquefort (or blue cheese) and Camembert cheese.
The fungal threads grow in and on the cheese, feeding on this
land of plenty and creating each cheese's distinctive texture,
flavor, and color.
These molds produce structures (conidiophores)
that produce millions of pigmented spores (conidia) resulting
in the bluish veins we are familiar with. Legend has it that
a shepherd boy eating his lunch of cheese curds by the mouth
of a cave near Roquefort, France temporarily abandoned
his lunch (to pursue a girl). When he returned (he must
have been gone for quite some time for the mold to grow) he
was famished and ate his moldy cheese. Apparently he
wasn't turned off by the new powerful favor.
I can't vouch for the historicity of the legend, but I
do know that Penicillium roquefortii grows in those caves.
Moreover, to be officially dubbed Roquefort cheese, the mold used in
the ripening process must be originally obtained from those
caves. If the cheese is produced using the same species of
mold (Penicillium roquefortii) yet traces its genealogy to
another location other than those caves, it must be called by
some other name, usually blue cheese.
I have attempted to give you an elementary
introduction to the microbiology of cheese using just a few examples,
but keep in mind that there are hundreds of kinds of
cheese. Some are moldy and some are not. This is a good
reminder that many more creatures great, small, and microscopic
that may appear useless or malignant now, could be a rich
future blessing from God. We may not see it yet because of
our dulled curiosity, creativity, and imagination. But I am
quite sure that there are many more creatures able to bless
mankind in countless ways, utilitarian, aesthetic, or culinary.