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How do you remove oxalic acid from spinach?

Spinach is a leafy green vegetable that is packed with nutrients like vitamin A, vitamin C, iron, and calcium. However, spinach also contains a compound called oxalic acid, which can bind to minerals like calcium and prevent them from being absorbed by the body. While oxalic acid is found in many healthy plant foods, some people are sensitive to it or want to remove it from spinach to maximize nutrient absorption.

The good news is that there are a few simple preparation methods that can help remove oxalic acid from spinach and other leafy greens. This article will cover everything you need to know about oxalic acid in spinach and how to get rid of it through boiling, steaming, baking, and blanching.

What is Oxalic Acid?

Oxalic acid is a naturally occurring compound found in many plant foods like leafy greens, beans, berries, and nuts. It’s what gives spinach that slightly bitter, acidic taste.

Chemically speaking, oxalic acid is a dicarboxylic acid that binds to calcium and other minerals to form crystals called oxalates. Oxalate crystals can be abrasive and irritating if consumed in large amounts.

For most people, the oxalate content in foods like spinach is not a problem. However, those with kidney problems, gout, rheumatoid arthritis, or vulvodynia may need to limit dietary oxalates to avoid symptoms.

Health Effects of Oxalic Acid

In moderation, the oxalic acid in spinach and other healthy foods is not harmful. But in large amounts, it can:

  • Bind to minerals like calcium and iron, preventing absorption
  • Cause kidney stones in those predisposed
  • Aggravate pain and inflammation in gout or rheumatoid arthritis
  • Contribute to vulvodynia (chronic pain of the vulva)

People who are prone to kidney stones are often advised to limit high-oxalate foods. For others, the benefits of eating oxalate-containing vegetables generally outweigh the risks.

Oxalic Acid Content of Spinach

Spinach contains one of the highest amounts of oxalic acid per 100 gram serving compared to other vegetables:

Vegetable Oxalic Acid (mg per 100g)
Spinach 750
Collard greens 610
Beet greens 610
Chard 530
Kale 500
Parsley 380
Broccoli 120

As you can see, spinach tops the list with 750mg of oxalic acid per 100g serving. For comparison, other veggies like broccoli contain significantly less.

Benefits of Removing Oxalates from Spinach

If you don’t have a specific health condition that requires restricting oxalates, keeping them in spinach and other healthy foods is fine. However, some potential benefits of removing oxalic acid from spinach include:

  • Improved mineral absorption: Oxalic acid can bind minerals like calcium, zinc, magnesium and make them unusable by your body. Removing oxalates may increase the bioavailability of these important minerals.
  • Kidney stone prevention: Those prone to oxalate kidney stones are often advised to limit dietary oxalates from foods like spinach.
  • Reduced inflammation: For some people, oxalates may aggravate inflammatory conditions like gout or rheumatoid arthritis.
  • Decreased vulvodynia symptoms: A low-oxalate diet can help reduce vulvar pain and irritation in some women.

If you don’t have any issues with oxalates, then there’s likely no need to go out of your way to remove them from spinach. But for some people, a low-oxalate diet can be beneficial.

How Cooking Affects Oxalates in Spinach

Fresh, raw spinach has the highest oxalate content. But cooking spinach using different methods can significantly reduce oxalic acid levels.

Here’s how different cooking techniques affect the oxalate content in spinach:

  • Boiling: Boiling spinach can leach out 30-87% of oxalates, according to studies.
  • Steaming: Steaming spinach has been found to reduce oxalates by 8-53%, varying by steaming time.
  • Baking: Baking spinach reduces oxalates by 15-30%, according to limited research.
  • Blanching: One study found blanching spinach reduced oxalates by 30-44%.
  • Microwaving: Microwaving may lower oxalates in spinach by up to 80%.

As you can see, cooking has a significant impact on oxalate content. Boiling, microwaving, and blanching spinach seems to be most effective, while baking is more moderate. Steaming is typically the least effective method.

Best Methods to Remove Oxalic Acid from Spinach

If you want to maximize the reduction of oxalic acid in spinach, here are some of the best preparation methods to try:

1. Boil Spinach in Water

Boiling spinach in water is one of the most effective methods for lowering oxalate content.

To boil spinach:

  1. Add washed spinach to a pot filled with boiling water.
  2. Allow it to boil for 2-5 minutes, which has been shown to reduce oxalates by 30-87%.
  3. Drain the spinach through a colander and discard the water.
  4. The boiled spinach is now ready to eat or incorporate into recipes.

Try adding the boiled spinach to omelets, pastas, soups or casseroles to benefit from the reduced oxalate content.

2. Steam Spinach

Steaming spinach on the stovetop or in a microwave steamer can also decrease oxalates, though not as much as boiling.

To steam spinach:

  1. Place washed spinach into a steamer basket over boiling water.
  2. Steam for 2-4 minutes until the spinach is bright green and wilted.
  3. Remove the steamer basket and discard any excess water.
  4. Chop the steamed spinach and add it to your favorite recipes.

Steaming for a shorter time reduces fewer oxalates. So if you want maximum oxalate reduction, allow the spinach to steam for the full 4 minutes.

3. Blanch Spinach

Blanching involves briefly boiling vegetables then immediately submerging them in ice water to stop the cooking process. This method results in a 30-44% reduction in oxalates.

To blanch spinach:

  1. Prepare a bowl of ice water and set aside.
  2. Boil a pot of water, then add washed spinach. Allow to boil for 1 minute.
  3. Drain the spinach and immediately submerge it into the ice water for 1 minute to stop cooking.
  4. Remove spinach and squeeze out excess water before using in recipes.

Blanched spinach retains more texture and color than boiling while still reducing a decent amount of oxalates.

4. Bake Spinach

Baking spinach into casseroles, tarts, and pastries can also decrease its oxalate content, though not as dramatically as boiling. The reduction achieved depends on factors like temperature and baking time.

In one study, baking spinach at 300°F (149°C) for 30 minutes reduced oxalates by 30%. Higher temperatures and longer bake times result in more oxalate reduction.

When baking spinach, try adding it to:

  • Quiches
  • Frittatas
  • Casseroles
  • Tarts
  • Baked pastas

5. Microwave Spinach

Microwaving spinach has been found to decrease oxalates by up to 80% in some studies. However, results can vary based on microwave wattage and cooking time.

To microwave fresh spinach:

  1. Place washed spinach leaves into a microwave-safe bowl with 2-3 tablespoons of water.
  2. Microwave on high for 2-3 minutes until the spinach is wilted and decreased in volume.
  3. Drain any excess water and use the microwaved spinach as desired.

For frozen spinach, defrost it first and then microwave for 1-2 minutes on high before incorporating into recipes.

Other Tips to Reduce Oxalates in Your Diet

In addition to cooking spinach and other high-oxalate vegetables in ways that reduce their oxalate content, here are some other tips to lower dietary oxalates:

  • Soak and rinse: Soak high-oxalate foods like spinach in water for 30 minutes before rinsing several times. This leaches out some soluble oxalates.
  • Combine with calcium-rich foods: Consuming calcium-rich foods like milk or yogurt alongside meals with spinach can help bind with oxalates before absorption.
  • Use smaller portions: Stick to smaller portions of spinach and other high-oxalate foods, and round out meals with low-oxalate veggies like carrots, lettuce and cucumbers.
  • Drink plenty of fluids: Getting enough fluid prevents dehydration and dilutes oxalates, which may reduce kidney stone risk.

Should You Avoid Spinach Altogether if Sensitive to Oxalates?

For most people without specific health conditions, there is no need to avoid oxalate-containing foods like spinach altogether. The nutrients and health benefits of eating spinach likely outweigh any risks related to its oxalate content.

However, those who are prone to developing kidney stones or experience symptoms related to oxalates like gout, joint pain, or vulvodynia may want to limit dietary oxalates. This includes curbing intake of high-oxalate foods like spinach.

If you need to restrict oxalates but still want to enjoy spinach, try consuming it only occasionally in small portions. Be sure to prepare spinach using boiling, baking, or blanching methods to reduce oxalates.

Also, focusing on getting plenty of calcium from food sources like milk, cheese, and yogurt may help offset the effects of oxalates in spinach. Drinking adequate fluids is also recommended to prevent oxalate crystals from forming.

The Bottom Line

Oxalic acid is a naturally occurring compound in spinach that may cause issues for some people when consumed in excess. Luckily, using preparation methods like boiling, steaming, baking, blanching or microwaving spinach can significantly reduce its oxalate content.

While you don’t need to avoid spinach altogether if you are sensitive to oxalates, limiting intake and using proper cooking techniques can help keep oxalates in check.

By being mindful of how you prepare spinach and not overdoing portions, you can maximize its nutritional benefits while preventing potential adverse effects of its oxalic acid.