The Real Reason Spinach Shrivels When You Cook It

Those who love fresh spinach both raw and cooked might wonder just how the leaves that could make up a massive bowl of salad could shrink down to a couple of scant cups when cooked. Though spinach is easy to sauté and stir into tons of different dishes like pasta fillings, eggs, casseroles and grain bowls, it might take a lot more of the raw leaves than you realize to yield the proportion of spinach you want in the dish. That's all because of the way spinach shrinks up so much when it is cooked. But there is actually more behind the reason spinach leaves shrivel up than what you might realize. 

According to FoodPrint, spinach is made up of more than 90% water. Given that fact, home cooks who have cooked a lot of fruits and vegetables that contain a high percentage of water likely know that the water evaporates out when the produce is cooked, causing its volume to shrink. But there's another component to the makeup of spinach that causes it to shrink so much, too.

According to the Los Angeles Times, spinach also contains oxalic acid. This acid responds quickly and adversely to heat, and when spinach is exposed to the oxalic acid as it leaves the spinach, oxalic acid causes the cell walls within the spinach to break down. Further, covering the spinach and creating a kind of heat chamber will cause a double-dose of oxalic acid (versus if you sautéed or heated the spinach uncovered); cooked this way, spinach can shrink up and turn far more soggy than it otherwise would. 

Shrinking spinach isn't all bad, though. By cooking spinach and minimizing its size, it is much easier to consume more of it along with the many healthy nutrients the dark green leaves contain, SFGate explains. Even though some nutrients are lost during the cooking process, you can eat a far more concentrated amount of spinach when it shrinks, allowing you to get more nutrients than you would by eating a smaller amount of raw spinach in say, a salad.

So, don't overthink the natural shriveling of cooked spinach. It isn't necessarily a bad thing. Just be sure to avoid covering the leaves as they heat to avoid overly broken down or soggy spinach due to the release of the oxalic acid and water.