The spice of life

this one's sweet

Spices -- hot-weather friends
cilantro If spices look so useful in the laboratory, why are they popular only in some cuisines? Why did Indian cookery become a playground of spices, while the Scandinavians opted for the blandness epitomized by the translucent, gelatinous lutefisk (a lye-treated codfish that's almost an initiation rite among wannabe Norwegians here in The Why Files' home state).

In particular, why are tropical cuisines so reliant on spices? Do spices cover the taste of rancid foods, or does pepper cool us off by stimulating sweating? Are more spices simply grown near the equator?

Or did the use of spices arise as protection from the food-borne bacteria that are more problematic in warm climates? This view would elevate a preference for spices from a trait that helps us win chile-eating contests into a trait that helped humankind survive. In other words, a trait with evolutionary value.

The antibiotic hypothesis
Paul Sherman, who studies behavior from an ecological perspective at Cornell University, found considerable evidence for the "antibiotic hypothesis" during a massive study of who uses spices and why (see "Antimicrobial Functions of Spices..." in the bibliography). And while it's impossible to pin the global distribution of spice preferences entirely on one factor, the antibiotic hypothesis seems to be the king of the hill, the speculation that must be disproven.

cardamom cardamomSherman together with undergraduate student Jennifer Billing defined spices as any plant-derived flavoring element added to food. Thus they considered seeds like coriander and cardamom, fruits like chile pepper, and leaves like rosemary, cilantro and oregano, and roots like onion, garlic and ginger.

Cooking the cookbooks
To test the hypothesis, Sherman and Billing examined 4,578 traditional meat recipes from 36 countries. They chose meat recipes because carnivorous fare carries more foodborne illness than vegetarian. The researchers counted which spices were specified how often in the recipes, then compared how spices were used in countries with various average temperatures. Although fungi and yeasts also cause gastrointestinal disease, Billing and Sherman focused on bacteria, the most common cause of gut aches.

After looking at the use of 43 flavorings, he found:

bullet The higher the average temperature of the country, the greater the proportion of recipes calling for at least one spice. Every recipe in 10 hot-weather countries required at least one spice, compared to only 67 percent of Norwegian recipes.

bullet The higher the average temperature, where food-borne pathogens would be expected to be most intense (before refrigation), the greater the use of spices that inhibit more than 75 percent of bacteria. "This means that more powerful spices are used more frequently in hotter climates," Sherman and Billing wrote, (the news hardly comes as a shock to veteran tropical travelers or Mexican-cuisine aficionados).

bullet Ten of the 43 spices had positive correlations with temperature: hot peppers, garlic, onion, anise, cinnamon, coriander, ginger, cumin, lemongrass and turmeric. Only dill and parsley had negative correlations and were used more often in cool climates.

bullet Black pepper, lemon and lime were used in meat recipes in every cuisine, even though they are among the least effective anti-bacterials. Black pepper, for example, inhibited only 38 percent of bacteria. Still, all three flavorings work together with other spices to increase their anti-bacterial oomph.

Although this correlation sounds convincing, the fact that A is correlated with B does not prove that A causes B. (Famously, the rooster's crow may not cause the dawn that always seems to follow it.) And some experts continue to say there's a more common-sensical explanation -- that tropical people eat more spices because they grow more spices.

The feeling of fire
gingerThat doesn't make much sense, Sherman argues, since there was no correlation between average temperature and the number of spices grown in a country. And it doesn't explain why people began to actually like the fiery taste of chiles, either.

But there's more evidence for the antibiotic hypothesis. Many spices, or their active chemical ingredients, can kill bacteria or inhibit them (slow their growth). Four common flavorings (onion, garlic, oregano and allspice) kill or inhibit every one of up to 29 common food-borne bacteria that they've been tested against. And most spices inhibit more than half of all bacterial samples.

The antibiotic hypothesis also has historic roots in the sense that plants, like humans, have had to evolve chemicals to deal with pathogens and parasites. The chemicals that give spice plants their distinctive flavor, Sherman and Billing wrote, "probably evolved to counter biotic enemies such as herbivorous insects and vertebrates, fungi, pathogens and parasites," and many bacteria and fungi that live on dead plants and animals cause disease in people. (Intriguingly, spices have been used to embalm bodies -- perhaps the ultimate test of antibiotic prowess.)

Finally, spices have figured heavily in history. When the Goths besieged Rome in 408 A.D., they demanded a ransom of 5,000 pounds of gold -- and 3,000 pounds of pepper. Marco Polo, Christopher Columbus and Hernando Cortes were among many explorers who changed history while seeking a faster route to the spice-rich Indies. And salt, another essential food flavoring and preservative, was once traded for equal weights of gold in West Africa.

Spice up your life with our toothsome bibliography.


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