Microscope Minutiae: The Micrococcus Microcosm

Meet the miraculous microbes responsible for curing safe-to-eat sausages since before the invention of refrigeration.

| Fall 2019

Photo from Wikimedia Commons/Josef Reischig

Renaissance sausage-makers may not have known about the health benefits of nitrites, but they did know that salting meat and curing it in open air limited spoilage. Sodium nitrate and sodium nitrite salts both serve to inhibit the growth of the bacteria Clostridium botulinum, and Listeria monocytogenes. These bacteria are responsible for manifesting toxic diseases when ingested — botulism and listeriosis, respectively — but they won’t stand a chance of survival in nitrate- and nitrite-heavy environments. Modern science has revealed that sodium nitrite is also useful in treating cyanide poisoning because it reacts with hemoglobin to create methemoglobin, a form that can’t transport oxygen, but will bind with cyanide and neutralize it. The dilatory effect of consuming nitrites may also be useful in treating high blood pressure and heart disease.

Three genera of bacteria appear to be the agents of the most notable changes in salami, pepperoni, and other dry fermented sausages: Lactobacillus and Pediococcus increase the acidity of the sausage, which limits further spoiling, while Micrococcus bacteria get to work converting nitrates into nitrites. The nitrites then combine with myoglobin, a meat protein, to create nitrosylmyoglobin — the complex that gives cured meats their pink or red color.

Micrococcus spp., a diverse group of spherical bacteria, are naturally occurring on human skin, as well as in meat and dairy products, soil, sand, and water. They’re gram-positive, which means they have thick, rigid cell walls, and they thrive in high- moisture, low-acid conditions. Micrococci are also obligate aerobes; to benefit from their action, meat must be cured in a well-ventilated area.

Wikimedia Commons/Alonnardi

So why do we encourage micrococci to grow in the early stages of creating dry fermented sausages? Briefly, because nitrites are more beneficial to us, but nitrates are easier to come by in the natural world. To transform them into the more beneficial nitrites, we must rely on the Micrococcus bacteria. Sodium nitrate salt — or curing salt — is a naturally occurring mineral; the largest pure deposits are in Chile and Peru, but small amounts of sodium nitrate infiltrate salt deposits around the world, and it’s also found in a number of vegetables. Salt and other spices are added to the chopped or ground meat and fat to produce dry fermented sausages ranging from Portuguese chouriço and Slavonian kulen to French saucisson sec and Italian salami.



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