There are widespread beliefs about why green vegetables lose their color and what it takes to retain their nutrients. For instance, does covering green vegetables while they cook change their color? Some say no, others say yes. There’s a confusing array of opposing thoughts from professionals and home cooks.
How to keep vegetables looking green
There appears to be consensus around three ways to keep vegetables green.
- Cook shorter times; Ricardo Media suggests cooking no more than 7 minutes, as well as adding acid, such as vinaigrette, at the last moment to avoid changes in color.
- Blanch greens and shock them in an ice bath.
- Use baking soda to keep vegetables green, although they soften and lose vitamin C.
The two most contradictory theories center around whether to add salt and keep the cover off when cooking vegetables. Do these actions impact color?
Salt has a slight effect on color. According to Ricardo Media, salt does protect chlorophyll, but minimally. Fine Cooking asserts that salting water hastens the cooking process by breaking down vegetable fibers and minimizes nutrient loss.
I microwaved two sets of green beans for 3 minutes, covered and with 1 tablespoon water. Although my photo could be better, it was apparent that salted green beans (left) were slightly greener and less wrinkly than unsalted green beans (right).
Covering green vegetables has no discernible effect on the color. Many would concur that keeping the lid on heats food faster, with no observable change in color. A covered pot may even preserve nutrients. Conversely, others have pointed out that keeping the lid on can concentrate natural acids that leak out of green vegetables, thereby destroying chlorophyll and discoloring vegetables.
In the below experiment both sets were salted and microwaved 3 minutes with 1 tablespoon water. To the naked eye there was no apparent difference in color between the covered and uncovered green beans. The uncovered green beans (left) were less cooked and their water had evaporated, leaving behind salt particles.
How to prevent vegetables from losing their nutrients
While beautiful green vegetables make for an attractive dish, minimizing nutrient loss is also a critical consideration when preparing vegetables. If discarding vegetable juices ever bothered you, you were right to be concerned. Below are key takeaways from some reliable sources (Healthine, see References).
Use as little water as possible when cooking, as water soluble vitamins C and B, as well as minerals, can be lost in the water. Thus, consuming the juices lost in the water is recommended.
Cook as short a time as possible. (coincides with how to keep vegetables green)
Don’t use baking soda as vitamin C will be lost.
Cut vegetables as little as possible, do not peel them, and cook them right away to avoid prolonged exposure to air.
Pair an acidic vitamin C ingredient with non-heme iron (iron not derived from meat) food sources. Iron in dark green leafy plants and fortified cereals is not well absorbed by the body. Acidic vitamin C, found in strawberries, kiwi and citrus foods, causes iron to be released better from non-heme iron sources, making it easier for the body to absorb the iron. Although acid can break down the color of green vegetables, dressing your salad at the last moment with a citrus dressing or drinking orange juice with your fortified breakfast may help absorb iron better. [3][7]
Salt the water. According to Fine Cooking, salting the cooking water minimizes nutrient loss as well as speeds up the cooking process by breaking down vegetable fibers.
Select a “healthy” cooking method. My subjective ranking below:
- Steaming. Steaming reduces vitamin C content by 9-15%.
- Microwaving. Microwaving green vegetables can lose about 20-30% of vitamin C in vegetables.
- Sauteing and stir-frying. Sauteing and stir-frying at high heat and for shorter times retains vitamin B. Adding fat also improves the body’s absorption of plant compounds and antioxidants. However, the percent of vitamin C degradation is unclear but considered significant.
- Roasting and baking. Roasting and baking have minimal loss of vitamin C, but extended cooking times at high temperatures may cause significant vitamin B loss.
- Boiling, poaching, simmering and stir-frying/boiling. Boiling, poaching and simmering can lose as much as 50% of C and up to 60% of minerals and vitamin B.
- Frying. Frying preserves vitamin C and B, but causes toxic substances linked to cancer and other diseases.
- Grilling and broiling. Grilling and broiling may cause significant loss of vitamin B and minerals, and result in cancer-causing substances to form.
One study from the Journal of Zhejiang University found that Vitamin C loss for stir-frying was 16%, stir-frying/boiling was 38% and boiling was 33%. These numbers are not on par with Healthline’s percentages above under cooking method rankings.
After digesting all the data, one would conclude that consuming raw vegetables is the best way to avoid nutrient loss. Albeit, one caveat is that harmful bacteria, such as Salmonella, E. coli and Listeria, can lurk on foods.
Related recipe:
References
- How Cooking Affects the Nutrient Content of Foods. Healthline.
- Kidney Stone Diet Plan and Prevention. National Kidney Foundation.
- Iron and vitamin C: the perfect pair? Michigan State University Extension.
- The Trick To Maintaining Color In Your Cooked Vegetables. Mashed.
- The Right Way to Cook Vegetables. Fine Cooking.
- Fruit and Vegetable Safety. Foodsafety.gov.
- Chemical reactions of vitamin C with intravenous-iron formulations. PubMed.gov.
- Check out how the way you cook influence the colour of your food. Chef Kamila.
- Does Sauteing Vegetables Take out Their Nutritional Values? SFGATE.
- What is the healthiest way to cook vegetables to maximize their nutritional value? The Globe and Mail.
- Effects of different cooking methods on health-promoting compounds of broccoli. Journal of Zhejiang University Science.