Learn the science behind:
It’s not easy to color a brown cake red. But that’s exactly what you try to do when making a red velvet cake.
This cake contains a good amount of cocoa powder, which originally contributed to the red-brownish hue. But nowadays, a slight red hue is no longer sufficient. People expect their red velvet cakes to be bright red.
That’s easy enough to accomplish if you have a bottle of strong (artificial) red food coloring. These colors are stable under just about any conditions. However, making a brown cake turn red with a natural food color such as beetroot requires a little more effort and a good squeeze of acid!
Red beetroot batter makes brown cake?
Have you tried coloring your red velvet cake with beetroot before? Whether that’s with special beetroot coloring powder, or by using whole mashed beetroots? Did you start out with a nice red batter, but still ended up with a brown cake?
Then you’ve already encountered the challenge of using beetroots as a colorant in food.
The color of beetroots can be bright red, but, it’s not stable under all conditions. If you want your cake to be just as red as your batter, you need to control the pH of your cake. That sounds more daunting than it is though. In practice, it means: don’t add baking soda and add plenty of acids!
Do not use baking soda to leaven your beetroot cake.
Beetroot color is sensitive to pH
So why do you need to be so careful with baking soda and acids?
The molecule responsible for the red color in beetroot is quite sensitive to the pH-value of its surrounding liquid. This molecule, called betanin, changes color when the pH-value changes.
Acids stabilize betanin
The pH-value is a measure for the acidity of your batter in this case. Betanin is red in color under acidic conditions, that’s a pH-value below 7. It’s most stable at a pH of 4-6. Under alkaline conditions it turns purple, instead of red. And, it becomes quite unstable.
When baking your cake, the betanin heats up. If the cake batter is acidic, the batter will prevent it from breaking down. However, if it is not sufficiently acidic, the betanin molecules break down in the oven. As a result, your final cake will be brown instead of red!
Making a red beetroot cake
You can color a cake red using just beetroots, or beetroot powder, without using any other colorant. However, keep in mind the following:
Refrain from using baking soda
Baking soda is an alkaline ingredient, with a pH well above 7. It can turn the whole batter alkaline. As a result, even if your batter is still bright red, your baked cake may turn brown in the oven. Instead, use baking powder. Baking powder also contains baking soda, but, it’s balanced out by added acids and doesn’t affect your cake as much.
Add plenty of acid
As you’ll see in the recipe below, we add 3 tbsp of lemon juice to our red velvet cake batter. You don’t actually taste any of this in the final recipe. Instead, it’s purely there to ensure the cake remains red during baking. You could probably still add a little more, without it impacting taste.
Instead of lemon juice, you can use vinegar, yogurt, buttermilk, or another acidic ingredient to help stabilize the color. Keep in mind that lemon juice is one of the strongest acids we use in food. You might need more of the other acids for a similar effect, though it depends on the exact recipe how much you need.
Where does red velvet come from?
Wondering where red velvet cakes even came from? So did we!
Red velvet cakes seem to have their origins in the USA where they were made before (artificial) bright red food colorings became available. But, they really started to rise through the ranks when artificial food coloring did become more common in the 30s and 40s of the previous century.
The ‘original’ red velvet cakes probably weren’t bright red, but more of a red-brownish color. They’d have gotten their color from the cocoa powder in the cake. Under the right conditions, cocoa can also get a slight red hue, as we saw when comparing a range of different cocoa powders.
What about the velvet?
So why red velvet? Velvet cakes existed well before the red velvet entered the scene. Velvet cakes had a finer, lighter texture than other cakes due to the use of low-protein flours such as almond or corn flours (current cake flours are also low in protein).
Patent No. US 8460739 B2, Process for making red or purple cooca material, link
Patent No. US 8709524 B2, Process for preparing red cocoa ingredients, red chocolate, and food products, link
Severson, Kim, Red Velvet Cake: A Classic, Not a Gimmick, May 12 2014, New York Times, link
Spence, Charles, 2015, On the psychological impact of food colour, Flavour, 21, 4, 1, 10.1186/s13411-015-0031-3, link