Cookies or bars turned green?

What you see: The cookies or bars you baked with sunflower seed butter are a dark bluish green. 
What it is: A harmless chemical reaction involving a common plant compound called chlorogenic acid.
Eat or toss: Eat! Maybe even make them special for St. Patrick’s Day!

Sunflower butter turns baked goods green

When EatOrToss reader Beth Gingold set out to bake peanut butter bars to share with her family, she needed to avoid nut allergens. So she skipped the titular ingredient and reached for a jar of sunflower seed butter instead. 

Everything mixed and spread into the baking dish just fine. But after Beth pulled the dish out of the oven and started slicing, it was clear that something hadn’t gone quite right. The bars were green!

Beth was alarmed, but as the founder of Recycle Leaders, an organization that helps people reduce waste, she definitely didn’t want to throw them away. With a little sleuthing, she determined that they were safe to eat. And not only that, “They tasted great,” she reported to EatOrToss. “And basically like peanut butter bars, which I was craving – they didn’t taste “green” (that is, they didn’t taste weird, they just looked weird).”

Huzzah for avoiding food waste and eating well! Even in the face of unsettling color changes. Here’s what happened to Beth’s bars and why it’s no big deal:

Sunflower seeds are rich in chlorogenic acid

At the root of the color change is a common plant compound called chlorogenic acid. Sunflower seeds are loaded with the acid, which is known for its antioxidant, anti-inflammatory and other human-health promoting properties. Coffee is especially rich in the stuff, with chlorogenic acid making up four to nine percent of the dry weight of green arabica coffee (however, the acid breaks down to varying degrees during roasting; up to 100 percent breakdown has been observed in dark roasts). Chlorogenic acid is also found in foods like apples, tomatoes, sweet potatoes and oranges. Loyal EatOrToss readers may recognize it as the culprit behind gray areas that develop on boiled potatoes. 

Why sunflower seed butter turns green when baked

Chlorogenic acid starts out clear. But when it’s in an alkaline (as in, the opposite of acidic) environment like Beth’s batter, it reacts with proteins, especially those in flour, causing the color change. To achieve blue-green baked goods, you need to have chlorogenic acid and protein in an alkaline environment

“If you don’t have those three things, then there’s no green,” Lilian Were, a food science professor at Chapman University told me. She started studying the phenomenon after a perplexed student asked for her take on unexpectedly green dessert bars a number of years ago. 

Sunflower seed butter cookies get greener with time

While chlorogenic acid breaks down when coffee beans are roasted at high temperatures, the comparatively “cool” oven heat doesn’t break down the acids and instead speeds up the reaction causing the blue green color, Were said. If Beth hadn’t put the batter in the oven and just left it on her counter, it would have eventually turned green, even at room temperature.

Moisture also accelerates greening as it provides a medium through which the various chemicals can find each other. Indeed, when sunflower seed butter cookies are first removed from the oven, it’s common to only see the green coloring on the inside. That’s because it’s the most moist part of the cookie. Over time, the reaction will spread closer to the surface. If the air is humid, the extra moisture will cause the color to take over faster. 

For example, here are two sets of sunflower seed butter cookies from the same batch. One set has been stored in the open air. The other has been in a plastic bag, which trapped moisture, creating a more humid environment. 

Image from Chlorogenic Acid Oxidation and Its Reaction with Sunflower Proteins to Form Green-Colored Complexes. Sabrina R. Wildermuth, Erin E. Young, and Lilian M. Were. Comprehensive Reviews in Food Science and Food Safety. Institute of Food Technologists. 2016. Image used with permission from one of the authors. 

How to prevent your sunflower seed butter cookies from turning green

Honestly, I think the green is pretty nifty and would just roll with it. But if you’re baking with sunflower seed butter and want to avoid making treats that look like something an unlikely hero might eat before gaining superpowers, consider altering your batter or dough chemistry. Generally, using more acidic ingredients and fewer basic (as in alkaline) ones will help (remember that acidic substances are low in pH while alkaline ones are high in pH).

Depending on the recipe, you might: 

• Use honey as a sweetener. Honey has a low, more acidic pH, especially compared to maple syrup which has a high pH and will intensify greening. 
• Use acidic dairy ingredients, like yogurt, buttermilk and sour cream. Only if they make sense in your recipe, of course.
• Add some lemon juice. Again, only if it makes culinary sense.
• Cut the amount of baking soda you use (Sunbutter suggests reducing it by a third.)
• Use banana instead of egg. Eggs can be alkaline, so trading them out for another protein or a more acidic binding ingredient could help. 

None of these methods is guaranteed to hold off the color change, but you can experiment to find ratios that work for your recipe. Interestingly, using honey as a sweetener might also make your cookies darker, because of the chemical structure of its sugars. (This is related to some of the chemistry we discussed in this post about brown areas on potato chips.) 

Straight from Professor Were’s lab, here are cookies baked with honey vs. maple syrup. The honey really made a difference!

Image from Chlorogenic Acid Oxidation and Its Reaction with Sunflower Proteins to Form Green-Colored Complexes. Sabrina R. Wildermuth, Erin E. Young, and Lilian M. Were. Comprehensive Reviews in Food Science and Food Safety. Institute of Food Technologists. 2016. Image used with permission from one of the authors. 

Greening in sunflower butter cookies has nothing to do with chlorophyll

While the term, “chlorophyll,” a pigment that gives plants their green, sunlight-absorbing color, might sound similar to “chlorogenic acid,” the two compounds are unrelated, sharing only a little etymology (“chloro-” comes from the Greek for “light green”). 

Were points out that chlorophyl is more similar to myoglobin, a protein that provides oxygen to muscles and comes in red, purple and brown shades, than it is to chlorogenic acid.  

It’s not easy being green!