A sharp-eyed reader noticed that our recipe for braised green beans called for adding a tenderizing ½ teaspoon of baking soda (Cooking, September 8). Now wait just a minute, Roberta Star Hirshson of Cambridge observed, “I was taught in nursing school never to add baking soda to cooking vegetables because it destroys the nutrients.”
That got us curious — just how damaging is baking soda? So we got in touch with an expert, Guy Crosby, who teaches at the Harvard School of Public Health, is science editor for America’s Test Kitchen, and coauthored 2012’s The Science of Good Cooking with the editors of Cook’s Illustrated. Turns out cooking food with baking soda (a.k.a. sodium bicarbonate) can indeed damage a number of nutrients, such as vitamin C, vitamin D, riboflavin, thiamin, and one essential amino acid. Yet it doesn’t hurt others, including vitamin A, vitamin B12, niacin, and folic acid.
“But what I find most interesting,” Crosby says, “is that the Massachusetts Water Resources Authority adds sodium carbonate to the water from the Quabbin Reservoir in order to decrease the leaching of copper and lead from old pipes.” The addition of sodium carbonate, a chemical cousin to baking soda, increases the pH level of Boston’s drinking water to approximately 9.3 (and raises the sodium content of an 8-ounce glass of the stuff to about 9 milligrams, a fraction of your daily allowance). However, that alkalinity usually gets neutralized during cooking by the small amounts of acid in many fruits and vegetables.
And that’s what saves at least some of the at-risk nutrients in this particular green-bean recipe: Any further damage that might have been done by the alkaline baking soda, Crosby says, will be halted after cooks stir in the acidic tomatoes.