Like bitter flavors, sourness is nature’s way of waving a red flag over a substance that is unripe, spoiled, or otherwise inedible. But for those of us who don’t mind a bit of tartness, this warning signal may actually be the first sign of some healthy benefits.
We can taste sourness thanks to receptors on our tastebuds that detect hydrogen ions from organic acids found in certain foods. Many of these acids occur naturally and are part of a food’s flavor profile, such as citric in lemons, tartaric in tamarinds, and oxalic in leafy greens.
Unripe fruits are particularly sour before becoming sweeter, since their acids are eventually broken down during the ripening process and their acerbic taste replaced by natural sugars. Other acids in foods are due to additives like acetic acid (used to make vinegar) or as a result of fermentation, which produces lactic acid in pickled produce like sauerkraut and cultured dairy such as yogurt.
Nature may have intended sourness as a warning not to consume indigestible substances, but when it comes to sour-flavored food (and with apologies to Friedrich Nietzsche), that which doesn’t harm you may actually be very good for you.
According to Ayurvedic principles, sourness triggers the salivary glands, thereby stimulating the appetite and signaling the start of the digestive process. Similarly, fermentation is likened to a kind of pre-digestion: lactic acid bacteria, used in cultured dairy, break down lactose (milk sugar), making tart-tasting milk products such as yogurt more digestible for the lactose intolerant.
Organic acids in sour foods aid with nutrient absorption: citric acid increases iron absorption, lactic acid helps to maximize calcium intake, while malic acid, found in fruits such as sour cherries and apples, has been combined with magnesium to treat fibromyalgia and chronic fatigue syndrome.
Sour tastes can be found in many foods enjoyed around the world, from sauerkraut to sour cream and from salted green mangoes to fried green tomatoes. Foods soured through fermentation, such as pickled vegetables, sourdough bread and yogurt, may be eaten on their own, while other fermented products, such as vinegar, and naturally tart edibles like lemons and unripe fruits, can be used as souring agents in other dishes.
One of the tastiest ways to include sour flavors is in soups. A savory variety is enjoyed in many countries: Thai tom yam, Vietnamese canh chua, Chinese suan la tang (more commonly known as ‘hot and sour soup’), Korean kimchi jjigae, Russian sour schi and Polish zurek all offer some tangy zest to their versions of this comfort food.
Few cuisines, however, hold sourness as a defining characteristic the way Filipino food does. Numerous dishes are classified by cooking methods in which tart flavors from vinegar and other souring agents are key, such as adobos, atsaras (pickled vegetables), and kinilaw (seafood marinated in vinegar or citrus juices), to name a few.
Ask Filipinos what they consider to be the national dish and many will name sinigang, a simple, flavorful sour soup. Thanks to an abundance of tangy produce available year-round in the Philippines, fresh souring agents used for sinigang include green mangoes, ripe guavas, calamansi juice, and tamarind (both its tender leaves and unripe fruit). For those without access to these ingredients, lemons, green tomatoes and tamarind paste are satisfactory alternatives.
Sinigang na Isda (Sour Soup with Fish)
5 cups prepared fish stock
1/2 cup peeled and finely diced daikon radish
3/4 cup green beans, cut into 1/2" pieces
1 lb cod or haddock fillet, skinned and cut into strips (salmon is also good)
2 tomatoes, seeded and chopped
1-2 cups bok choy, stems stripped and leaves torn or sliced into strips
1-2 Tbs tamarind paste
Salt and black pepper
Pour prepared fish stock into a large pan and add daikon radish. Bring to a simmer.
Add green beans and continue cooking at a gentle simmer for about 5 minutes.
Add the fish, tomatoes and bok choy. Add tamarind paste and stir until it dissolves into the broth. Bring the soup back to a gentle simmer and cook for another 5 minutes, or until fish is cooked through.
Season with salt and black pepper to taste. Serve with steamed rice or enjoy on its own.
Tracey Paska lives, eats and writes in Manila, Philippines, where she revels in the fact that she can wear flip-flops outdoors in January. When she's not exploring Manila's foodscape, she freelances for a national food magazine and writes about the complex and fascinating connections between food, culture, and society on her blog Tangled Noodle.