Blue, a color that evokes tranquility, depth, and the vastness of the ocean and sky, is surprisingly elusive when it comes to our plates. Walk through any grocery store, and you’ll notice a vibrant spectrum of colors in the produce aisle – reds, greens, yellows, oranges, and purples abound. But truly blue foods? They are a distinct rarity. This begs the question: Why Are You Blue so hard to find in the natural world of edibles? And when we do encounter foods labeled as blue, what’s the science behind their captivating hue?
For a color so prominent in nature overall, blue’s scarcity in food stems from the fascinating world of plant pigments. While we’ve previously explored the science of food colors and how to maintain their vibrancy, the case of blue foods takes us into a more peculiar and almost experimental realm. Dive into the science of blue foods, and you might feel a bit like a food scientist yourself, armed with kitchen tools instead of lab equipment, ready to uncover the secrets behind this enigmatic color in our meals.
The Anthocyanin Enigma: Nature’s Color-Changing Chameleon
The majority of foods that exhibit a blue or bluish hue owe their color to a group of pigments called anthocyanins. These fascinating compounds are responsible for a wide range of colors in plants, from vibrant reds and purples to, yes, blues. However, anthocyanins are notoriously unstable, acting like color-changing chameleons depending on the pH levels of their environment.
Red cabbage serves as the quintessential example of this pH sensitivity. Depending on whether it’s exposed to acidic or basic conditions, red cabbage can dramatically shift in color, morphing from bright red to purple, blue, or even a dark blue-green. Generally, anthocyanins tend to lean towards the blue and purple end of the spectrum in basic (alkaline) environments and shift towards purple and red in acidic ones.
So, you’ve discovered a food that appears blue? The immediate scientific curiosity should be: what happens when you introduce an acid? In most cases, adding an acid to a blue food will cause it to transform into a purplish shade. Conversely, if you have a purple food and add acid, it’s likely to turn red.
Here’s the catch, the major hurdle in cooking with blue: almost all foods are inherently acidic to some degree. This acidity presents a significant challenge in preserving the blue color when preparing and cooking naturally blue foods. So, how can we possibly cook with blue and maintain that coveted hue?
Fortunately, nature and culinary ingenuity offer a few exceptions. There are foods and preparation techniques that minimize the introduction of acids, allowing the blue hue to persist. Sometimes, a clever culinary trick – like a tiny pinch of baking soda – can help tip the pH balance just enough to retain or even enhance the blue. Furthermore, some anthocyanins exhibit less dramatic color changes, offering more flexibility in cooking methods while still providing a touch of blue.
Let’s delve into the world of blue foods, categorizing them into those reliant on anthocyanins for their color and others that derive their blue from different pigment sources. Prepare to explore the almost magical, sometimes unpredictable, world of blue cuisine.
Blue/Purple Anthocyanin Powerhouses
Blueberries: These beloved berries are often the first food that comes to mind when thinking of blue. Freshly picked blueberries certainly appear blue, but observe them closely when crushed – they quickly reveal a red or purplish undertone. The pigment in blueberry skin is indeed blue at a neutral pH. However, the natural acids within the berry itself shift the color towards red when the berry is disrupted.
When it comes to blueberries, flavor often trumps color in culinary applications. The slightly acidic tang of blueberries is a key component of their deliciousness. Interestingly, blueberries can even turn greenish if exposed to a strong base, such as an excess of baking soda or baking powder in pancake batter or muffin mixes. To prevent this unwanted discoloration, you can either reduce the leavening agents in your recipe or counter their basicity by adding a touch of acid, like lemon juice or buttermilk.
Blue Corn: Certain varieties of corn boast a stunning blue hue, thanks to their rich anthocyanin content. Similar to red cabbage, blue corn’s color is also influenced by pH. In acidic conditions, blue corn will lean towards purple, while in basic conditions, it will exhibit a truer blue. Experiment with substituting blue cornmeal for yellow cornmeal in recipes like cornbread or tortillas to add a visually striking and subtly different flavor dimension to your dishes.
Red Cabbage (The Blue Food Dye Secret): Red cabbage, despite its name, holds the key to creating a natural blue food coloring. When cooked red cabbage leaves are steeped in a slightly basic solution, they transform into a bluish-purple liquid. To make a blue food dye, slice red cabbage leaves and boil them for 10-15 minutes. Strain out the cabbage and reduce the liquid until it thickens into a syrup (the liquid from a whole cabbage can reduce to about a quarter of a cup). This concentrated syrup will be intensely purple.
Now for the magic trick: add a tiny pinch of baking powder (sodium bicarbonate) – and we mean tiny. Proceed with extreme caution, adding baking soda in very minute amounts until the color just shifts to blue. Overdoing it can easily push the color to green, and also negatively impact the flavor. The goal is to add just enough baking soda to achieve the blue color without significantly altering the taste.
The resulting blue dye, surprisingly, has a relatively mild flavor despite its cabbage origin and the addition of baking soda. Use it sparingly to add a touch of blue to icings, cake batters, and cookies. However, remember the fickle nature of anthocyanins – if you incorporate this blue dye into an acidic food, it will likely revert back to purple.
Purple Potatoes: These potatoes are a visual delight. Raw, they display a vibrant purple hue. However, cooking brings about an intriguing color shift – they transform into a brilliant blue-purple. While the exact chemistry behind this change is complex, it seems to be a different type of color alteration than the typical acid/base reactions seen with other anthocyanins.
Cooked purple potatoes are less susceptible to color changes from acids compared to red cabbage or blueberries. However, exposure to very high concentrations of acid can cause them to bleach, turning them a very pale purple, quite unlike their intense raw color. Another advantage of purple potatoes is their resistance to color bleeding during cooking. These qualities make them a wonderful way to introduce unusual color to a plate without excessive worry about pH-induced color changes. Beyond their visual appeal, purple potatoes are nutritional powerhouses, packed with anthocyanins, giving them a nutritional edge over white and yellow potatoes. Try substituting them in your favorite potato recipes for a colorful and healthy twist.
Cornflowers (Bachelor’s Buttons): Cornflowers, also known as bachelor’s buttons, are known for their striking bright blue blossoms. These edible flowers can be used fresh in salads or as an elegant garnish for desserts. Dried cornflowers also make a beautiful garnish. Their flavor is very mild and grassy, meaning they are primarily used for their visual contribution. Some loose-leaf tea blends incorporate cornflowers, creating a visually stunning contrast with the dark tea leaves. As with any edible flower, ensure you source them from a reputable supplier who can guarantee they are organically grown or treated only with food-safe chemicals.
Borage: Borage is an Italian herb characterized by its delicate blue flowers. Often grown as a companion plant near tomatoes and eggplant, borage produces large, textured leaves and clusters of small, five-pointed blue flowers. Traditional folk medicine even suggests that borage flowers can elevate mood. And indeed, the simple act of adding these pretty blue flowers to your plate is likely to bring a smile. Use fresh borage flowers in salads or as a charming garnish for desserts.
Butterfly Blue Pea Flower: The butterfly blue pea flower is arguably the most visually stunning of the blue anthocyanin-containing foods. This pea vine produces blossoms of an intensely vibrant blue. Culinary traditions in Thailand, Malaysia, Burma, and China have long embraced this beautiful flower. Pulut tai tai, a Malaysian sticky rice cake flavored with coconut and pandan, gets its characteristic blue speckles from butterfly pea flowers. Chor ladda, an intricately shaped Thai dumpling, resembles a bright blue flower thanks to this natural dye.
In Thailand, these flowers are also used to make a refreshing chilled herbal tea, believed to have cooling properties. Butterfly pea flowers can be used fresh or dried to create an incredibly vibrant blue infusion. Dried butterfly pea flowers are particularly remarkable, yielding a deep, electric blue color. Their flavor is mild, herbal, with a subtle hint of cucumber. However, like other anthocyanin-based blue colors, the brilliant blue of butterfly pea flower infusions will readily transform to a bright purple upon the addition of acids, such as lemon juice. This color-changing property makes butterfly pea flower tea a fun and interactive beverage, as you can watch the color shift with a squeeze of lemon.
Beyond Anthocyanins: Other Sources of Blue
Blue Cheese: Stepping slightly outside the plant kingdom, we encounter blue cheese. Its distinctive blue veining doesn’t come from anthocyanins. Instead, blue cheese gets its characteristic color from specific mold cultures introduced during the cheese-making process. The particular mold species varies depending on the type of blue cheese, but they all belong to the Penicillium genus – the same group that gives us penicillin (though consuming blue cheese will not cure a sinus infection!).
The blue color in blue cheese is typically quite deep and is not prone to bleeding or changing color. When serving blue cheese in cold dishes, try using a cheese wire to cut it into thin sheets. This reveals the beautiful mottled surface of the blue veining, making for a much more visually appealing presentation than crumbles.
Pickled Garlic (The Unexpected Blue): Sometimes, the question isn’t “why is it blue?” but “why did it turn blue?”. Pickled garlic can sometimes undergo an unexpected color transformation. When raw garlic is pickled, trace amounts of sulfur in the garlic can react with minuscule amounts of copper present in your water or cooking utensils. This reaction can result in the garlic turning a blue-green hue over time (often taking a few weeks to become noticeable).
This blue color is not due to anthocyanins but rather to the formation of copper sulfate. While the amount of copper sulfate formed in pickled garlic is harmless, it’s important to remember that copper sulfate is toxic in larger quantities. If you wish to prevent your pickled garlic from turning blue, a simple solution is to briefly boil the garlic cloves before adding them to the pickling brine.
Bluefoot and Blewit Mushrooms: These mushrooms, while often described as blue, might appear more purplish to the discerning eye. However, they are indeed referred to as blue mushrooms, and they possess both a fantastical appearance and a unique, remarkable flavor. Bluefoot mushrooms are available in specialty stores in some regions, often carrying a premium price tag due to their relative rarity. Blewit mushrooms are related but even harder to find in certain areas.
Blewit mushrooms tend to be more uniformly blue-purple, while bluefoot mushrooms exhibit blue coloration primarily at the base of their stems. Bluefoot mushrooms are prized for their rich, woody, and meaty flavor. Like many flavorful mushrooms, their taste intensifies and spreads beautifully when cooked with cream, making them a luxurious addition to sauces and creamy dishes.
In conclusion, the quest for blue foods unveils a fascinating intersection of food science, culinary artistry, and the sometimes unpredictable nature of plant pigments. While true blue foods may be scarce, their rarity only amplifies their appeal and makes the culinary exploration of their unique properties all the more rewarding. So, next time you encounter a blue food, take a moment to appreciate the science and natural wonder behind its captivating color.
