Kale is a nutritious leafy green vegetable that has gained popularity in recent years for its health benefits. However, kale also contains compounds called oxalates which can be problematic for some people. Oxalates bind to calcium and can contribute to kidney stone formation in susceptible individuals. For people prone to kidney stones or other health issues related to oxalates, removing oxalates from kale may be desirable.
In this article, we will examine methods for reducing oxalates in kale to make it safer for consumption. We will cover simple preparation techniques like boiling and steaming as well as more intensive processes like fermenting and pickling. Read on to learn how to remove oxalates from kale!
What Are Oxalates?
Oxalates are naturally occurring compounds found in many plant foods like leafy greens, nuts, seeds, fruits and vegetables. Oxalic acid is the simplest dicarboxylic acid and binds strongly to minerals like calcium, iron and magnesium. When oxalates bind to calcium, an insoluble salt called calcium oxalate is formed which cannot be absorbed by the body.
Excess oxalates can increase risk for kidney stones in susceptible individuals. Kidney stones affect around 1 in 11 people in the United States. Calcium oxalate stones are the most common variety, comprising around 80% of all kidney stones. Even small amounts of oxalates over time can contribute to kidney stone development.
Individuals with a history of calcium oxalate kidney stones, gout, rheumatoid arthritis, vulvodynia or other conditions related to oxalates may need to restrict dietary oxalates. For these individuals, reducing oxalates in high oxalate foods like spinach, beet greens, and kale can be beneficial.
Oxalate Content of Kale
Kale contains significant levels of oxalates. Per 100 grams, raw kale contains around 305 mg of oxalates. This oxalate content is much higher than other common vegetables:
|Vegetable||Oxalate Content (mg per 100g)|
While oxalate content can vary between cultivars and growing conditions, kale generally contains high levels of oxalates compared to many other vegetables. Individuals prone to oxalate-related health issues may need to limit intake of raw kale. However, there are effective methods to help remove oxalates from kale.
Boiling is perhaps the simplest method to reduce oxalates in kale. The blanching action helps draw out water-soluble oxalates from the leaves.
One study found that boiling kale for 5 minutes removed on average 32% of oxalates. Increased boiling time can further eliminate oxalates – boiling for 10 minutes removed 35% while 20 minutes removed 41% of oxalates.
To boil kale:
– Chop kale leaves into bite-sized pieces and wash thoroughly.
– Bring a pot of water to a rapid boil. Add the chopped kale and blanch for 5-20 minutes.
– Drain in a colander and rinse under cool water to stop the cooking process.
Boiling for just a few minutes can help reduce some of kale’s oxalate content. However, longer boiling times extract more. Boiling for 10-20 minutes appears most effective for lowering oxalates.
Like boiling, steaming kale can help reduce oxalate content. Steaming cooks the leaves with hot steam rather than submerging in boiling water.
In one study, steaming kale for 9 minutes removed 24% of oxalates on average. Longer steaming times of 18 minutes extracted around 28% of oxalates.
To steam kale:
– Chop kale and place in a steamer basket or metal colander.
– Bring water in a pot to a boil below the basket.
– Steam for 9-18 minutes, until leaves are tender.
– Remove basket and run under cool water to stop cooking process.
Steaming retains more nutrients than boiling but is slightly less effective at removing oxalates. Still, steaming for 10-15 minutes can reduce around a quarter of kale’s oxalates.
Pickling kale in an acidic brine solution helps break down and leach oxalates from the leaves. Fermentation by lactic acid bacteria further reduces oxalate content.
One study found pickling decreased oxalates in kale by 34% on average. Oxalate levels continued to drop the longer kale was pickled.
To pickle kale:
– Thoroughly wash and chop kale leaves.
– Prepare a brine of water, vinegar, salt, spices and sugar. Bring to a boil.
– Pack kale into sterilized jars and pour over hot brine.
– Seal jars and allow to pickle for 1-4 weeks to allow oxalates to leach out.
The longer kale pickles, the lower the oxalate content. Pickling for 1-2 weeks can reduce around a third of oxalates in kale.
Like pickling, fermenting kale with lactic acid bacteria can effectively degrade and reduce oxalates.
One analysis found that fermenting kale eliminated on average 38% of oxalates. Further fermentation for longer periods degraded more oxalates.
To ferment kale:
– Chop and wash kale thoroughly. Massage leaves to help start releasing liquid.
– Pack leaves into a sterilized glass jar, pressing down firmly. Top with a bit of brine if needed to submerge leaves.
– Seal jar and allow to ferment for 1-4 weeks. Check periodically and press leave back under brine as needed.
– Once desired sourness is reached, transfer to the refrigerator.
Fermenting kale for just 1-2 weeks can help drop oxalate content by over a third. More extended fermentation further reduces oxalates while also providing beneficial probiotics.
Other Tips for Lowering Oxalates
In addition to cooking methods, there are other ways to help reduce oxalate content when preparing kale:
– Soak in an alkaline solution. Soaking kale in baking soda and water for a few minutes can help draw out some soluble oxalates.
– Discard cooking liquid. The water used for boiling, steaming or blanching kale contains leached oxalates, so draining this liquid helps remove oxalates.
– Add calcium-rich foods. Calcium binds to oxalates so they cannot be absorbed, so adding a calcium source like cheese, yogurt or milk may help.
– Limit portion sizes. Restricting kale servings to 1⁄2 cup cooked kale at a time can help prevent excessive oxalate intake.
– Increase fluids. Drinking more fluids may help dilute oxalates and decrease kidney stone risk when consuming higher oxalate foods.
Healthier Ways to Enjoy Low Oxalate Kale
Here are some tasty and nutritious recipes using low oxalate kale prepared by methods like steaming, pickling or fermenting:
– Kale salad – Toss steamed then chilled kale with ingredients like avocado, chickpeas, carrot, olive oil, lemon, and Parmesan cheese. The cheese provides calcium to bind oxalates.
– Kale chips – For crispy low oxalate kale chips, bake steamed kale leaves coated in olive oil and seasonings.
– Pickled kale stems – Ferment the stem portion of kale to create tangy, probiotic-rich pickled kale stems to use like pickles.
– Kale pesto – Process steamed kale with olive oil, garlic, walnuts, and Parmesan to make a fresh pesto sauce perfect over pasta or fish.
– Kale soup – Puree steamed kale with broth and cream to make a velvety low oxalate soup. Top with crumbled bacon or croutons.
– Sauteed kale – Quickly saute boiled kale with garlic and olive oil for an easy cooked green side.
With a few preparation tricks, people prone to kidney stones or other oxalate-related issues can still enjoy kale and receive its many nutrients. By boiling, steaming, fermenting or pickling kale, oxalate levels can be decreased by 25-40% or more. Monitor serving sizes and pair with calcium-rich ingredients to further improve oxalate absorption. With tasty ways to prepare low oxalate kale, oxalate-sensitive individuals can still reap kale’s nutritional benefits.
Kale contains beneficial nutrients like vitamins, minerals and antioxidants but also provides high levels of oxalates. For individuals prone to oxalate-related health issues like kidney stones, reducing kale’s oxalate content can allow safer consumption. Simple preparation techniques like boiling, steaming, fermenting and pickling have been shown to decrease oxalates in kale by 25-40%. Combining these cooking methods with proper portion sizes, discarding cooking liquid, adding calcium-rich ingredients and drinking plenty of fluids can all help support low oxalate kale consumption. With some easy preparation tricks, even individuals sensitive to oxalates can enjoy kale’s nutritional benefits while avoiding potential risks.