Friday, April 8, 2011

How to cook spinach and silverbeet to reduce oxalic acid

It really sent me into a spin recently when I read over at Healthy Home Economist that it's best not to eat spinach and silverbeet raw. Whaaat? Why?

Apparently because they contain oxalic acid, which "blocks iron and calcium absorption and may contribute to the formation of kidney stones."

*UPDATED: I was so gutted about this, but then my friend Jessica did some digging and discovered several published studies that have proven it's not so bad eating raw spinach after all. This is especially true if you consume probiotics regularly - in natural yoghurt and kefir.

I'm still not eating as much raw spinach and silverbeet as I used to - we're not including it in our smoothies anymore, but I'm fine to put spinach leaves in salads and on hamburgers.

If you are at all concerned about this, or have a history of kidney stones, oxalic acid can be reduced by a light steam or boil. Tip out the cooking water though, as that's where the oxalic acid ends up.

I had a bit of spare time recently, so I cooked up a big batch of spinach and then a big batch of silverbeet and froze them in ziplock bags to use in lasagne and frittatas in the future. I don't like the taste of cooked spinach much, so I have to disguise it in meals with lots of other ingredients.

The process
1. Bring a big pot of water to the boil.

2. Cut the stalks out of your spinach / silverbeet / kale.

3. Thoroughly wash the leaves.

4. Throw leaves into the pot of boiling water and cook for exactly one minute. (If your water stops boiling when you add the leaves, you can start the timer from when the water starts boiling again. Just watch your leaves to ensure they're not getting overcooked and blackened.)

5. Tip out into a strainer and pour cold water over the cooked spinach until it is completely cool. (This prevents it from over-cooking and turning black.)

6. Squeeze to remove excess water.  (For some reason this photo rotates when I upload it, and I can't see a way to rotate it to its correct position. Anyone know what that's about?)

7. Chop up finely. (This helps me disguise it in meals. I've even been known to puree it in the food processor.)

8.  Store in the quantities you want in labelled ziplock bags in the freezer until ready to use. (Suck all the air out of the ziplock bags to prevent freezer burn.) (This photo is doing the weird rotate thing too. Any ideas how to fix that in Blogger?)

Whenever I'm making a mince-based dish like lasagne or Asian pork mince, I chuck one of these bags of cooked spinach in it (minus the bag). We hardly notice it's there, but it packs a great nutritional punch.


  1. Thanks Emma, the frozen boiler spinach now makes sense!

  2. Totally cool article. Just discovered the whole raw spinach/silverbeet thing with kidney stones which I have a history of. I've been juicing these like popeye everyday for ages! Adrian - NZ

  3. Also found a NZ study to support your post :) "Soluble oxalic acid reduced 84-87% by cooking" This is a great paper from Lincoln University (Canterbury): Page 2 has some interesting info.

  4. Sorry to put the proverbial 'cat among the pigeons' but my wife and I have recently suffered poorer health after increasing our daily intake of 'cooked' only green leafy from the beet family (kale, collards, beets, silverbeet). We have had a reasonable amount most days for breakfast and have suffered calcium deficiency. My friend showed me Dr Norm Walker's jucing book in which he states (pg 56) that oxalic acid is not only beneficial but essential for digestive health in its RAW form. However when you cook it becomes inorganic and is destructive and binds to calcium including that in other foods in the same meal, destroying the nourishing value of both. This results in such a serious deficiency of calcium that it has been known to cause decomposition of bones! We have suffered this and so I will no longer eat nor can recommend to anyone cooked beets. I will be only eating them raw from now on. I know this is the opposite of much opinon out there, however the reputation of the man in regards to heath and diet is much greater than those of the contrary opinion and his understanding explains our experience.

    1. It's always good to hear other perspectives Gusman. Thanks for your input. I'll endeavour to find out more about this. Cheers, Emma

  5. Susan W (Perth)
    Over 30 yrs ago my dad who had kidney stones was told to avoid spinach because of oxalic acid. Researching this yrs later I discovered that it was safe for us if it was eaten raw. (I'd talk to a specialist if one had kidney problems though.) But I mostly use home grown baby spinach leaves that are small indeed - not the pre-picked bags from the supermarket. The raw stuff always agreed with me whereas the cooked stuff sometimes caused "problems" which lines up with the bit about calcium binding with the acid and being leached out of the body. I stick with spinach being good for health if raw and unsprayed. Just my experience.
    A word of advice - my mum used to say that if we ate fifty different foods, good foods obviously, per week we would get an assortment of elements and minerals etc that the body needs. I always remember this when choosing menus for family meals and when buying veg, fruits or cooking breakfast cereals. Stick to unprocessed foods and make it yourself you know what you're putting into it.
    Haven't read yr blog here accidentally while looking up 'spinach'. All the best..


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