What Exactly Are Preservatives? Ask Paul

A preservative is any ingredient added to food to limit spoilage. When the topic of preservatives in food comes up, it’s very often in phrases such as “loaded with preservatives” or “free from preservatives”—the implicit assumption, of course, being that preservatives are harmful. But are preservatives actually bad for you?

No: For almost as long as humans have been preparing food, we’ve been preserving it.

Some traditional preservation methods are physical: keeping food cold, for example, or drying it out. But a great many of the oldest preservation methods are chemical. Smoking meat and fish not only makes it taste great, but it also infuses the surface with a wealth of chemical components, including phenolics and carbonyl compounds, that prevent the growth of bacteria and molds.

Many common spices also have powerful preservative effects, including vanilla, rosemary, oregano, and cinnamon. In her Swedish kanelbullar, deputy food editor Andrea Geary had to increase the amount of yeast, because the cardamom in the recipe is such a strong antimicrobial that it was killing off the yeast cells.

And one of the primary ways that fermentation preserves food is by creating lactic acid, another powerful preservative chemical.

Acids

The most common job of a preservative ingredient is to keep microbes at bay, and the most common way of doing that is by adding an acidic ingredient, since most microbes can’t survive acidic environments. Examples include citric acid, acetic acid, sorbic acid (sometimes in the form of potassium sorbate), lactic acid, and fumaric acid.

Antimicrobials

Many other ingredients can also keep microbes such as bacteria and fungi from proliferating. These include spice extracts, sodium benzoate, and sodium nitrite (sometimes listed as “celery powder” on ingredient lists).

Antioxidants

Apart from microbes causing spoilage, oxidation is the main enemy of stored food. It causes fats to go rancid, flavors to change and degrade, and colors to turn brown and dingy. All of these are due to reactions between oxygen in the air and components in the food. Antioxidant additives typically work because they’re more readily reactive with oxygen than food is, so oxygen reacts with them instead of with the food. Common antioxidant ingredients include ascorbic acid (vitamin C) and sulfur dioxide (common in dried fruit), tocopherol (vitamin E), and BHT (which is chemically synthesized but also occurs naturally in lychees).

Most of the preservatives used in food are not associated with any adverse health reactions. And many of them are ingredients that we eat in other forms in greater quantities anyway, like the acids in fruits and spices in home cooking.

Some preservative ingredients are known or suspected to have negative health effects, however. Some people, such as asthma sufferers, are sensitive to sulfur dioxide. Sodium nitrite can form potentially carcinogenic nitrosamine compounds, which is why the advice to limit consumption of cured meats is now widespread. As with almost everything, moderation is the key.

Ask Paul Adams, senior science research editor, about culinary ambiguities, terms of art, and useful distinctions: paul@americastestkitchen.com