Spinach often grows well in sandy soil, and unless it is very well rinsed it may feel gritty.
Spinach contains some oxalic acid.
Rhubarb, which is sour enough to set your teeth on edge, owes its sour taste to oxalic acid, which can be gritty.
However, the variety of spinach that accumulates the most oxalic acid has only 7 percent by dry weight, much less in the form of raw spinach, and it is not grown commercially.
Oxalic acid was formerly thought to prevent absorption of the iron in spinach by binding to it, but the latest measurements by the United States Department of Agriculture’s Plant, Soil and Nutrition Laboratory indicate that it does not seem to bind the iron, so Popeye was right, the laboratory says.
The recommended daily requirement of iron is 10 milligrams for men.
Popeye would have to eat quite a bit of spinach to get the daily allowance. Raw spinach has about 2.7 milligrams of iron per 100 milligrams, or about two cups of chopped spinach.
Popeye’s favorite, a half cup of canned spinach, including the liquid, has about 1.85 milligrams of iron.
Other good vegetable sources of iron are dandelion greens, Swiss chard and kale.
Some dried fruits, like peaches, apricots and raisins, are also good sources of iron, but organ meats like liver are even better.
Why does eating spinach make your teeth feel funny? How much would Popeye have to eat to get his daily requirement of iron?