The Case of the Expanding Sausage Package
QUESTION: “We recently came across a package of cooked sausages that had remained "hidden" in back of our refrigerator about a month past it's "use by" date. The package had "blown up" to the size of a football. I assume this is because of bacterial or related organism growth.
Can you better explain this? I know that the food is not safe to eat, of course, but was wondering what types of bacteria might be the cause. There were no "added" bacteria, yeasts, etc. listed on the label.”
ANSWER
Various Bacteria are present in all foods, mostly in small amounts. Cold storage and heat treating (cooking) kills some bacteria, reduces the population of others (kills some of them) and slows the growth of others.
Various bacteria are used beneficially in fermentation of such products as yogurt and cheese, fish pastes and sauces, and yes even sausages. Fermentation frequently results in the production of various gases.
Some species of Staphylococcus and lactic acid bacteria are used in sausage production for flavor development.
Certain bacteria also work on undigested carbohydrates in the human intestine, producing gases such as carbon dioxide and hydrogen sulfide.
These are anaerobic bacteria - that is bacteria that grow in the absence of oxygen.
Some of the most powerful and dangerous bacteria are also anaerobic - such as Clostridium botulinum which results in botulism, which is frequently fatal.
The bacteria involved in the expanding package of sausages can be many varieties, actually many of them will not cause illness. BUT because the growth of bacteria is evident - this also indicates that any harmful bacteria that may have been present, have also multiplied. NEVER eat food from such packages.
A "simple" explanation of fermentation from the Encyclopedia Britannica:
“The term fermentation now denotes the enzyme-catalyzed, energy-yielding pathway in cells by which fuel molecules such as glucose are broken down anaerobically. In most cells the enzymes occur in the soluble portion of the cytoplasm. The reactions leading to the formation of pyruvate thus are common to sugar transformation in muscle, yeasts, some bacteria, and plants. One product of the pathway is always the energy-rich compound adenosine triphosphate (ATP). The other product, pyruvate, can undergo various transformations, depending on the cell type and the availability of oxygen.”
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