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Canning: Sealed with a Kiss—Plus Some Heat and Acid
Some of the items found at your local grocery are stored in cans and jars, which can last on your shelf for years. Join Groupon as we twist the lid off the science of canning.
From the bottom of the sea to the top of a mountain peak, microorganisms can appear almost anywhere on Earth. Within a jar, though, a serving of beans can last for months or even years without ever encountering a single microbe. This protection comes from a combination of factors that halt bacteria growth. Jars or cans are usually heated after they’re filled, killing the living organisms inside while also forcing out oxygen to create a vacuum seal. Still, some bacteria can survive even boiling temperatures, so another safeguard is needed. Luckily, most of the fruits in preserves, jams, and marmalades are highly acidic, as is the vinegar used to pickle cucumbers, beans, and loose change. The low pH level further prevents the growth of anything that could spoil the food on the shelf. Though there are rare cases in which anaerobic bacteria can survive in cans, the effect usually lasts for quite a while; scientists have even discovered edible brandied peaches and mixed vegetables in the wreckage of Civil War ships.
Indeed, the practice of canning is significantly older than our knowledge of the science behind it. Seeking an easier way to feed his troops, Napoleon—who famously said that “an army travels on its stomach”—offered a cash award to anyone who could discover an efficient means of storing and transporting rations. A French brewer named Nicholas Appert won the contest after observing that sealing food within heated glass jars prevented it from spoiling. He collected the prize—and Napoleon’s army ate—but the science remained a mystery until another Frenchman, Louis Pasteur, proclaimed that microbes were responsible for “spoiling” his roommate’s food.