The Secret To Bright White Buttercream Is Purple Food Coloring
Most people don't think twice about the color of butter — that is, until they turn it into buttercream frosting. Butter is naturally yellow-toned, meaning when combined with powdered sugar, vanilla, and milk, you're left with an off-white frosting. As delicious as it may be, sometimes you want your frosting to be bright white.
For best results, it's essential to start with butter that's lighter in color. Regular butter tends to be paler than organic butter. According to Live For Cake, grass-fed cows consume more beta-carotene and produce yellower milk and, ultimately, yellower butter. Even with organic butter, you can still get whiter buttercream simply by whipping it, Bakery and Cakery shares. Whipping breaks up the butter and sugar with air; thanks to the added volume, the frosting appears whiter. Opting for a non-organic butter and giving it an extra whip are surefire ways to reduce the yellowness of your frosting, but a more effective approach is one that may surprise you.
Color correcting buttercream
If you want the whitest, brightest buttercream, you might assume that adding food coloring would be the last thing you'd want to do. As it turns out, the opposite is true. In a viral TikTok video, @petitecakery shares that she adds the tiniest bit of purple food coloring to her frosting, and after a few rounds of mixing, the yellow tone is completely gone. This may seem too good to be true, but as Chels Sweets explains, the purple food coloring acts more like a color corrector than a dye. Purple and yellow are opposites; you can see their locations across from each other on the color wheel. When you combine the slightest bit of yellow from the buttercream with an equal amount of purple food coloring, the two neutralize each other. What's left is what we perceive as bright white. For best results, Bakery and Cakery suggests dipping a toothpick in the food coloring and adding only a little at a time as needed. Too much purple will overcorrect the yellow; instead of white, you'll end up with gray frosting.
It doesn't work with white chocolate frosting
If you plan to frost your cake with a white chocolate ganache, don't count on color-correcting it with purple food coloring because the technique is best reserved for buttercream. Even though it has white in its name, white chocolate ganache isn't actually white in color. Instead, according to The Little Vintage Baking Company, it's translucent and more on the yellow side. As @browniegod demonstrated in her TikTok, adding purple food coloring will either intensify the cream color or turn it almost green.
You'll need to whiten a chocolate-based frosting, not color-correct it. White food coloring, per Sweetness and Bite, isn't a dye but rather a titanium dioxide and glycerin. When added to the frosting, it whitens the mixture with chemical additives instead of neutralizing its color. A white food coloring will also work on a butter-based frosting, but it'll be just as effective if you have purple on hand.