by Dave DeWitt
There are a number of explanations for why we have added spices such as chile peppers to our foods over the tens or hundreds of thousands of years that we have been cooking. They are:
Spices make foods taste better.
The “eat-to-sweat hypothesis”–eating spicy foods makes us cool down during hot weather.
To disguise the taste of spoiled food.
Spices add nutritional value to food.
The antimicrobial hypothesis: spices kill harmful bacteria in food and aid in food preservation.
Which of these explanations are correct?
The First Cornell University Study
In 1998, Jennifer Billing and Paul W. Sherman published a study in The Quarterly Review of Biology that examined the reasons why humans might use spices. They studied 4,578 recipes from 93 cookbooks on traditional, meat-based cuisines of 36 countries; the temperature and precipitation levels of each country; the horticultural ranges of 43 spice plants; and the antibacterial properties of each spice.
The first thing they discovered was that many spices were incredibly antibacterial. For example, garlic, onion, allspice, and oregano were the best all-around microbe killers, killing almost everything. Next were thyme, cinnamon, tarragon, and cumin, which kill about 80 percent of all bacteria. Chile peppers were in the next group, with about a 75 percent kill rate. In the lower ranges of 25 percent were black pepper, ginger, and lime juice.
Next, they learned that “Countries with hotter climates used spices more frequently than countries with cooler climates. Indeed, in hot countries nearly every meat-based recipe calls for at least one spice, and most include many spices, especially the potent spices, whereas in cooler counties substantial fractions of dishes are prepared without spices, or with just a few.” Thus the estimated fraction of food-spoilage bacteria inhibited by the spices in each recipe is greater in hot than in cold climates, which makes sense since bacteria grow faster and better in warmer areas.
The researchers addressed the various theories. First, obviously spices make food taste better, “But why do spices taste good? Traits that are beneficial are transmitted both culturally and genetically, and that includes taste receptors in our mouths and our taste for certain flavors. People who enjoyed food with antibacterial spices probably were healthier, especially in hot climates. They lived longer and left more offspring.”
Billing and Sherman discounted the “eat-to-sweat” theory, noting that not all spices make people sweat and that there are easier ways to cool down, like moving into the shade. Regarding the theory that spices mask the odor of spoiled food, they noted that it “ignores the health dangers of ingesting spoiled food.” And since spices, except for chiles and citrus, add minimal nutritional value to food, that theory goes nowhere.
That leaves just two theories: that spices make foods taste good, and that they kill harmful bacteria–and those two theories are inseparable. “I believe that recipes are a record of the history of the coevolutionary race between us and our parasites. The microbes are competing with us for the same food,” Sherman says. “Everything we do with food–drying, cooking, smoking, salting or adding spices–is an attempt to keep from being poisoned by our microscopic competitors. They’re constantly mutating and evolving to stay ahead of us. One way we reduce food-borne illnesses is to add another spice to the recipe. Of course that makes the food taste different, and the people who learn to like the new taste are healthier for it. We believe the ultimate reason for using spices is to kill food-borne bacteria and fungi.”
The Second Cornell University Study
In 2001, Paul W. Sherman and Geoffrey A. Hash continued the examination of spices in human diet with a study entitled “Why Vegetable Recipes Are Not Very Spicy,” published in Evolution and Human Behavior. They compiled information from 2,129 vegetable-only recipes from 107 traditional cookbooks of 36 countries. Then they examined the history of the spice trade and discovered that for thousands of years spices have been traded all over the world, resulting in their availability in most world cuisines. The most traded spices are black pepper and chile pepper, in that order.
Many studies have proven the antibacterial properties of spices, the fact that spices are more prevalent in warm climates than cool climates, and that the concentrations of spices in recipes are sufficient to kill bacteria. It is true that cooking eliminates the antimicrobial properties of some spices, such as cumin, but has no effect on others, such as chiles.
The researchers compared the vegetable-only recipes to the previous study of meat recipes according to the spices found in the recipes and discovered that vegetable recipes used far fewer spices than meat recipes. They attributed this to the fact that bacteria “do not survive or proliferate as well in vegetables, so adding spices is not as necessary.” Interestingly, the four most common spices in both the meat and vegetable recipes were onion, black pepper, garlic, and chile peppers. Onion appeared in more than 60 percent of both types of recipes; black pepper in about 60 percent of the meat recipes and 48 percent of the vegetable recipes; garlic in 35 percent of the meat recipes and 20 percent of the vegetable recipes; and chile peppers in 22 percent of the meat recipes and 18 percent of the vegetable recipes.
Within countries, vegetable-based recipes called for fewer spices than meat recipes in all 36 countries. The countries using the most spices in both vegetable and meat recipes were, in order from the most used: India, Vietnam, Kenya, Morocco, Mexico, Korea, and The Philippines. Following were France, Israel, and South Africa.
In their second study, the researchers concluded: “By every measure, vegetable-based recipes were significant less spicy than meat-based recipes. Results thus strongly support the antimicrobial hypothesis.”
Top 30 Spices with Antimicrobial Properties
(Listed from greatest to least inhibition of food-spoilage bacteria)
Source: “Antimicrobial Functions of Spices: Why Some Like It Hot,” by Jennifer Billing and Paul W. Sherman, “The Quarterly Review of Biology,” Vol. 73, No.1, March 1998.
10. Lemon grass
11. Bay leaf
12. Chile peppers
26. Pepper (white/black)
28. Anise seed
29. Celery seed