If you work with fondant–and since you’re reading this you probably do–you’ve likely found that purple fondant quickly fades to a shade of blue that barely resembles its formerly purple self. I was researching the issue and came across this Flour Confections blog post which I read with fascination. The post begins:
When the FDA banned Red Dye No. 2 in 1976 after it was linked to cancer, the FDA-approved Red Dye No. 40 took its place. Compared to Red No. 2, Red 40, as it’s known in the industry, is less stable, more expensive, and requires anywhere from 30%-50% more color to achieve proper saturation. Red 40 is UV intolerant, so any UV light (including bright lights) will cause it to fade. Because purple is a mix of red and blue, when the red fades, the blue remains, and your purple fondant turns blue .
To prevent fading, store purple fondant and gumpaste out of the light, in a dark bag or container and in a cupboard. Keep finished cakes, flowers, decorations, etc. in a dark place for as long as possible. According to Lisa of Flour Confections, cakes that are airbrushed purple do not fade, so consider airbrushing your fondant purple instead of kneading in purple food coloring. You can also use a more stable colorant. SugarFlair colors are more concentrated than other food colors and their Grape Violet contains E122, a more stable red than Red 40. [Note: Sugarflair colors are not FDA approved for food use. I couldn't find them for sale in the U.S., but they are widely available in Australia and Britain.]
Finally, when the pH of your fondant or gumpaste is not balanced, the red can fade out. To balance the pH, you can add an alkali such as baking soda. A good ratio is 1 tsp of baking soda per 1 lb of fondant or gumpaste. This brings me to my blog post. I wanted to see for myself the effect of baking soda on purple fondant, so I conducted a little experiment.
I used both Wilton’s Violet and AmeriColor’s violet to test whether they fade differently. I colored a small amount of Satin Ice fondant. (I specify the fondant brand because I didn’t test to see if different fondants react with the color differently and fade differently.) The Wilton (on the left) is more of a true purple while the AmeriColor (right) is more of a periwinkle with a strong blue appearance.
I then added 1/4 teaspoon baking powder to 14 grams of each color (a much higher ratio than that recommended by Flour Confections) and left the remaining purple unaltered.
To ensure that the fondant would dry evenly, I rolled each piece to the same thickness using my KitchenAid pasta attachment.
The baking soda didn’t change the Wilton color at all at this point, but as soon as I kneaded the baking soda into the AmeriColor purple, the most fascinating thing happened! The AmeriColor turned from a periwinkle into a true purple. I couldn’t believe it!
I then set them directly in the blazing sun for an hour to see what would happen. (Note where the shadows from the food coloring containers are. These areas did not fade as much as you will see in the final photo.)
After an hour (give or take–I kind of forgot to time it), these are the results.
The unaltered AmeriColor purple (far left) actually retained the red (and remained more purple) than the AmeriColor with added baking soda. The Wilton fondant with added baking soda (far right) remained more true to color than the fondant without baking soda. For both brands, the fondant that was in the shadow of the food coloring containers held up way better than the fondant in the direct sun, demonstrating the importance of keeping purple fondant away from UV light.
Conclusions. Keep purple fondant away from UV light to prevent fading. Always do a test strip both with baking soda and without to determine the best way to retain the purple color. Note that other brands of fondant might react differently with purple and might fade differently. Know that some fading is unavoidable. And, of course, hope for the best!
Thanks so much to Lisa and Flour Confections for doing all the research and for allowing me to paraphrase their post. Their efforts have helped countless cake artists.