Why do we eat spices?

I love curries. My favorite is Indian tikka masala which is prepared with tomato, yogurt and many different spices including turmeric, ginger, garlic, cardamom, cumin, paprika, cloves and cinnamon. But I’m not the only one, because the passion for spicy dishes is shared among humans of all regions and ages. We eat them fresh, dried, whole, ground, raw or cooked, and our love for these tasty substances led explorers such as Polo, Magellan and Columbus to undertake risky expeditions in search of new routes for spice trade and, accidentally, even to the discovery of the American continent.

But why do we eat spices? An obvious and superficial answer is that aromas make food more inviting to our taste, smell and sight. However, this does not answer the deeper evolutionary question about the reason why spices are so appreciated. In other words, why do we like them?

Spices as antibacterials

The reason why plants produce and accumulate aromatic substances in their fruits, leaves, roots or bark is to protect from herbivores, fungi, pests and insects. Ironically, it may have been spices ability of keeping animals and pests away that attracted humans. Indeed, it seems very likely that the key of the success of spices in the kitchen resides in their antimicrobial properties. As if we had borrowed recipes plants use for protecting themselves against bacteria to use them in turn in a similar manner while cooking. By counteracting microorganisms growth we can better preserve foods and prevent food poisonings.

Some of the most common spices. In order: garlic head; cinnamon sticks; coriander seeds; parsley leaves; ginger rhizome; nutmeg (in this case still covered orange mace); cardamom fruits and seeds; turmeric rhizome and powder; chili pepper; basil leaves; onion; lemongrass; cloves (flower buds); fruit of star anise; cumin seeds; lime; sage leaves.

A pretty dated but comprehensive study has collected data on antibacterial properties of dozens of spices commonly used for cooking. Among the most effective, which could kill or arrest the growth of most bacteria on which have been tested, there are garlic, onion, oregano, thyme, cumin, cloves, bay leaf and pepper. Some of the bacteria that were unable to proliferate in the presence of these spices, included Salmonella, Escherichia, Shigella and Clostridium, very common bacterial species responsible for many foodborne diseases.

Several studies confirm that concentrations of spices used in cooking are sufficient to yield useful antibacterial effect that helps food preservation. However, this does not mean that they are suitable for treating bacterial infections; the concentrations required in this case would be high enough to have unacceptable side effects.

The hotter the spicier

To support the ‘spices as antibacterial’, the authors of this study assessed their use in thousands of recipes from the culinary traditions of 36 different countries. If the hypothesis is correct, one would expect a more generous use of spices in warmer regions, where the non-refrigerated food spoils very quickly.

We all tried firsthand such variability during a trip or dinner in an international restaurant, and who did the math has in fact found that the higher the mean annual temperature in a certain region, the greater the amount of spices that was used. It comes out that where it’s warmer a greater variety and a greater amount of spices is employed in each recipe. In India, for instance, where the average temperature is about 27°C, 25 different spices are commonly used and each recipe calls on average for 9.3. Instead cooking in Norway (about 3°C on average) involves the use of 10 spices only, less than two per recipe.

On the left, different spices are ordered according to their antibacterial effect, expressed as a percentage of inhibited bacterial species on those tested (maximum: garlic – 100%, minimum: lemon/lime – 23%). At the center, the spices are ranked according to the number of times that are required in the preparation of some 5,000 recipes from around the world (maximum: onion – 65%, minimum: fennel – <1%). The graph in the box relates the number of spices used in each recipe with the average temperature of the country from where the recipe comes from. With the temperature, not only the number of spices per recipe increase, but also the number of spiced recipes, the variety of spices and the overall antibacterial power of the dishes. Data source

Moreover, they noticed that spices with the highest antibacterial activity were the most common in recipes from around the world, and more abundantly used in warmer areas. Thus, the antimicrobial power of tropical dishes was fount to be greater that the one from temperate regions. This is also due to the fact that the substances contained in spices act synergistically when used together. Lemon and pepper for instance, which individually have a rather limited antibacterial properties, may potentiate the effect of other substances, by increasing the acidity of the media or phytochemicals bioavailability for microorganisms, respectively.

Some spices combinations are so common that they deserved special names. An example is the curry powder that contains up to 22 different spices or French quatre épices made with based pepper, ginger, cloves and nutmeg, to protect sausages from the proliferation bacteria responsible for botulinum poisoning.

Gastronomic evolution

In an evolutionary perspective, those who appreciated spicy food lived healthier and longer, and may have had a larger progeny. They had fewer bacterial infections and could store food longer, to better face the low-flow periods. Giving an evolutionary advantage, the pleasure of eating spicy food moved across generations both genetically -for instance by inheriting taste receptors- and culturally, through written and oral transmission of recipes. «Over time, recipes should “evolve” as new bacteria and fungi appear or indigenous species develop resistance to phytochemicals», and the amount and type of spices changed according to a process that rewarded the most beneficial recipes. With this in mind, say the authors, we can consider recipes as a «written records of our coevolutionary races against foodborne diseases».

A few days ago I heard about a seagull who was rescued after falling into a tikka masala pot. This happened in Britain, where in 2001 this recipe was declared national dish by the Foreign Secretary. Beside yellow stained feathers, the animal is fine. It is possible that spices are showing their beneficial effects also to non-human palate and gut?

– Sherman P., & Billing J. (1999). Darwinian Gastronomy: Why We Use Spices BioScience, 49 (6) DOI: 10.2307/1313553
– Billing J., & Sherman P. (1998). Antimicrobial functions of spices: why some like it hot. The Quarterly review of biology, 73 (1), 3-49 PMID: 9586227

Cover – CC BY 2.0Chili pepper – CC0, Coriander – CC0, Cinnamon – CC BY-SA 3.0, Cumin – CC BY-NC 2.0, Ginger – CC0, Turmeric – CC BY-SA 3.0, Cardamom – CC0, Garlic – CC0, Parsley – CC BY-SA 2.0, Basil – CC BY-SA 3.0Onion – CC BY-SA 3.0, Lime – CC0, Citronella – CC0, Nutmeg – CC0, Cloves – CC0, Star anise – CC0, Sage – CC0

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