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"Why do hotdogs plump when you cook them?"

Hi! I'm helping my 3rd grade daughter with her science project. She likes to cook and so after browsing through several science experiment topics, she decided to do this experiment about hotdogs and what happens to its size after cooking it. I couldn't find any book or Web sites that will be my resource on the scientific reason why a hotdog would increase its size or decrease its size after cooking. Thank you very much in advance.

—Cynthia from Florida


Still have more questions? You'll find more answers in our archived monthly feature articles by the Inquisitive Cooks.

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Hello Cynthia,

While we know of no specific studies on this, our feeling is as follows. Hot dogs (also known as frankfurters and wieners) are cooked and/or smoked sausages, prepared for sale according to government specifications. They may contain fat and water, as well as extenders such as nonfat or whole dry milk, or cereal.

The Food Safety and Inspection Service of the USDA suggests the following food safety guidelines. "Although all hot dogs are fully cooked, you should reheat them and make sure they are steamy hot throughout." Let's think through what's happening as hot dogs cook.

Our first thought is that both the powdered dry milk and the starches found in cereals are geared to absorbing moisture. Starches do not allow moisture to enter until they are heated. While cooking, however, heat breaks bonds within the starch granules, allowing moisture to enter so the starch swells.

Ingredients related to smoking and curing contribute to flavor, color, and preservation, but to our knowledge are not related to swelling.

Probably the most important factor at work is the extraordinarily power of water turning to steam as it's heated. Inside those hot dogs you'll find water added as an ingredient, along with water in the form of moisture within the meat, and possibly moisture within the fat, (depending on the type of fat) One volume of water can expand 1600 times as it turns to steam. No wonder those hot dogs swell. And no wonder they shrink as they cool!

Hot dog experts we invite your comments, and Cynthia, we're keen to know the results of your experiments!

Anne & Sue




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