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Prairie Fare: Can Rhubarb Become Toxic?

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Rhubarb provides vitamin C, fiber and lots of tart flavor in a wide range of recipes. Rhubarb provides vitamin C, fiber and lots of tart flavor in a wide range of recipes.
According to a widely circulated Facebook post launched in another state, rhubarb could become toxic (poisonous) after a frost. Could that be true?

By Julie Garden-Robinson, Food and Nutrition Specialist

NDSU Extension Service

Do you remember the “telephone” game? You might have played it when you were a kid.

In the game, one person whispers a message into the ear of the person next to him or her, then that person repeats the message to the person next to him or her and so on. By the end of the communication chain, the person announces what he or she heard.

Often, the last person in the line received a message that had little to do with the first message.

I experienced something like the telephone game last week, except this time, social media in the form of Facebook served as the “telephone.” As with the telephone game, by the time the message reached people and was repeated, it was a bit distorted.

All eyes were on rhubarb after the cold temperature blast. I had no idea people liked rhubarb this much.

I received phone calls, emails and questions via Facebook. People were talking about the avalanche of rhubarb information on their Facebook news feeds. Some people thought I had launched the “great toxic rhubarb campaign of 2015.”

“I didn’t do it,” I said when someone asked.

Some parts of North Dakota and other states had experienced untimely freezing temperatures. According to a widely circulated Facebook post launched in another state, rhubarb could become toxic (poisonous) after a frost. Could that be true?

According to the post, a hard freeze drives the naturally present toxin, oxalic acid, from the leaves into the rhubarb stalks.

I hadn’t nabbed any rhubarb from either of my neighbors, but after all this concern about rhubarb, I felt compelled to check out their rhubarb crops. Upon investigation, the leaves were not curled or discolored, and the stalks looked reddish green and ripe for making into cobblers, pies and other treats.

I grabbed a few stalks and we enjoyed the dessert recipe included with this column.

While at work, one of my students poked her head in my office and mentioned that someone in her apartment building was pulling up all her “poisonous rhubarb.” I was a little alarmed because I have a soft spot for rhubarb. This poor, defenseless, innocent rhubarb was reminding me of my childhood.

As a kid, I enjoyed bringing a cup of sugar to our garden and pulling a rhubarb stalk and dipping it in sugar. I wasn’t a food safety specialist back then, so I may have rinsed the rhubarb under a garden hose if my mother was looking.

When do you have to worry about rhubarb? Rhubarb in your garden that has frozen to the point where the stalks become damaged or mushy should be discarded. Check the leaves, too. If the stalks are firm and upright and the leaves have little damage, the rhubarb is OK. Discard the damaged ones and enjoy the stalks that grow later.

As with anything, when in doubt, don’t eat it.

Consuming large amounts of oxalic acid could affect your heart, digestive system and respiratory system. According to some sources, a person would need to consume 11 pounds of rhubarb leaves to reach a fatal dose.

During the World War I food shortages, people were encouraged to consume rhubarb leaves as a vegetable. That was not a good idea because oxalic acid is found in abundance in the rhubarb leaves. Rhubarb stalks naturally contain a very small amount of oxalic acid.

The usual issue of concern with oxalic acid-containing foods is the production of calcium oxalates in our body, which comprise kidney stones.

Heed the earlier warning: Do not eat any rhubarb leaves and you will be fine.

Have you ever heard the expression “the dose is the poison?” Many vegetables, especially leafy greens such as spinach, swiss chard, beet greens and cabbage, also contain small amounts of oxalic acid. If you eat the recommended amount of vegetables, you are consuming some of this natural chemical.

Please do not stop eating your vegetables, by the way.

Vegetables do not contain enough oxalic acid to warrant concern unless a person has a rare medical condition. If you have this condition, your health-care provider probably will refer you to a dietitian for help in knowing what foods to limit or avoid.

As I was talking about rhubarb and cold temperatures, someone overheard me.

“So you shouldn’t freeze your extra rhubarb because it will become toxic?” she asked.

The game of “telephone” was getting worse by the minute.

“You can freeze rhubarb in your kitchen for next winter,” I replied. “Just rinse it, cut it and freeze it in a single layer on a cookie sheet and pop it in a freezer bag,” I added.

Rhubarb provides vitamin C, fiber and lots of tart flavor in a wide range of recipes. Botanically, rhubarb is considered a vegetable, although we may think of it as a fruit because it is served in sweet desserts.

Enjoy some delicious rhubarb this season. Remove the leaves and discard them. Be sure to rinse rhubarb thoroughly under cool, running water.

Visit http://www.ag.ndsu.edu/food for more information about food preservation and more recipes.

I was so inspired by all this discussion that I bought a rhubarb plant to plant in our garden. Here’s one of the first recipes I learned to make from the rhubarb that my grandmother planted in the yard of my childhood home about 100 years ago. That was right around the time of World War I when people were advised to eat rhubarb leaves. My family must have ignored the recommendation.

Rhubarb Cake

1 1/2 c. brown sugar

1/2 c. butter

1 egg

1 c. buttermilk

2 c. flour

1 tsp. soda

1/2 tsp. salt

1 3/4 c. cut-up fresh or frozen rhubarb

1 tsp. vanilla

Topping (1/4 c. sugar and 1/2 tsp. cinnamon)

Preheat the oven to 350 F. Cream sugar and butter. Add egg and buttermilk; mix thoroughly. Sift flour, soda, salt; add to sugar-buttermilk mixture. Add vanilla and rhubarb. Pour into greased and floured 9- by 13-inch pan. Sprinkle topping over batter. Bake for 40 to 50 minutes, until a knife comes out clean.

Makes 12 servings. Each serving has 260 calories, 4 grams (g) of protein, 9 g of fat, 41 g of carbohydrate, 1 g of fiber and 230 milligrams of sodium.

(Julie Garden-Robinson, Ph.D., R.D., L.R.D., is a North Dakota State University Extension Service food and nutrition specialist and professor in the Department of Health, Nutrition and Exercise Sciences.)


NDSU Agriculture Communication – May 28, 2015

Source:Julie Garden-Robinson, (701) 231-7187, julie.garden-robinson@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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