Blue is a famously elusive colour in the natural food world. When we talk about “blue foods,” truly blue pigments, distinct from purplish or greenish hues, are exceptionally rare. Given this scarcity, we must appreciate the foods that lean even slightly towards blue. While the colour spectrum in previous food explorations might have focused on more common plant-based colours, venturing into blue territory takes us into fascinating and sometimes unusual culinary science.
My research for this article felt like a step into a food scientist’s lab – complete with pH strips, observations of mold cultures, and simmering pots of intriguing blue liquids. The majority of blue foods we’ll explore derive their colour from anthocyanins. These pigments are known for their instability, reacting notably to pH levels. Red cabbage serves as a prime example; it can shift dramatically from vibrant red to purple, blue, or even a dark blue-green, all depending on the acidity of its environment. Generally, anthocyanins that change colour tend towards the blue and purple range in basic conditions and shift to purple and red in acidic environments.
So, you’ve found a food you believe is blue? It’s a good bet that adding an acid will turn it more purple. Conversely, if you start with a purple food and introduce acid, it’s likely to become redder. Here’s the catch in this captivating pH-driven colour transformation: almost all foods are naturally acidic. This poses a challenge: how can we effectively cook with blue foods and maintain their desired hue?
Fortunately, there are exceptions. Certain foods and preparation techniques minimize acid exposure, thus preserving the blue colour. Sometimes, a touch of baking soda can even help (though this is a delicate balance). Additionally, some anthocyanin variations are less susceptible to pH changes, offering more flexibility in cooking while retaining a hint of blue.
To better understand this spectrum, we can categorize blue foods into two groups: those that rely on anthocyanins for their colour-changing properties, and those that derive their blue from other pigments. So, put on your metaphorical lab goggles and prepare for an exploration into the intriguing world of blue food.
Blue/Purple Anthocyanin-Rich Foods
Blueberries
Fresh blueberries present a beautiful blue hue when picked, yet crushing them reveals a red or purple interior. The skin’s pigment is blue under neutral pH conditions, but it shifts to red upon contact with the berry’s inherent acidity. With blueberries, flavour often outweighs colour considerations, and their characteristic tartness is a key part of their appeal. Interestingly, blueberries can even turn greenish if exposed to an overly alkaline environment, such as in pancake batter or muffin mixes. To prevent this green discolouration, consider reducing the baking soda or baking powder in your recipe, or enhance acidity by adding lemon juice or buttermilk.
Blue Corn
Blue corn varieties are naturally rich in anthocyanins. In acidic conditions, blue corn will exhibit a purplish tint, whereas basic conditions will enhance its bluer tones. Experiment by substituting blue cornmeal for traditional yellow cornmeal in recipes like cornbread or tortillas to add a vibrant colour twist and a slightly nutty flavour.
Red Cabbage
Red cabbage is a readily available natural blue food colouring agent. Cooked red cabbage leaves, when steeped in a mildly basic solution, will eventually turn a bluish-purple. To create a blue food dye, slice red cabbage leaves and boil them for 10-15 minutes. Strain off the cabbage, and reduce the remaining liquid until it thickens into a syrup. The liquid from a whole cabbage will reduce significantly to about a quarter of a cup of intensely purple syrup. Now, carefully introduce a tiny pinch of baking powder – precision is key here, as too much can shift the colour towards green. Continue adding baking soda in minuscule amounts until the desired blue shade is achieved. It’s crucial to use just enough baking soda to alter the colour without affecting the flavour negatively. Small amounts are usually imperceptible in taste, but overdoing it can make the dye unpalatable. This resulting blue dye, despite its humble cabbage and baking soda origins, has a surprisingly neutral flavour. Use it sparingly to add blue tints to icings, cake batters, and cookies. However, remember the colour’s sensitivity; adding it to acidic foods will revert it back to purple.
Purple Potatoes
Raw purple potatoes boast a vibrant purple colour, but cooking transforms them into a brilliant blue-purple. While the precise chemistry is complex, this colour shift appears to be different from typical acid/base reactions. Cooked purple potatoes are less prone to colour changes from acid compared to red cabbage or blueberries. Interestingly, very high acid concentrations can even bleach them to a pale purple, unlike the intense purple of their raw state. Furthermore, purple potatoes are less likely to bleed their colour during cooking. These characteristics make them an excellent choice for adding unusual colour to dishes without excessive concern for pH-related colour changes. Nutritionally, purple potatoes, packed with anthocyanins, offer an advantage over white and yellow potatoes. Try substituting them into your favourite potato recipes for a colourful and nutritious upgrade.
Cornflowers
Cornflowers, also known as bachelor’s buttons, are known for their bright blue hue. The blossoms are edible and can be used fresh in salads or as an elegant garnish for desserts. Dried flowers also serve as a beautiful garnish. Their flavour is mild and grassy, making them primarily a visual element. Some loose leaf tea blends incorporate cornflowers, creating a striking visual contrast with the dark tea leaves. As with all edible flowers, ensure you source them from reputable suppliers who can confirm they are organically grown or treated only with food-safe products.
Borage
Borage is a blue-flowering herb from Italy, often found near tomatoes and eggplant in gardens. The borage plant features large, textured leaves and clusters of small, five-pointed blue flowers. Folk medicine traditions suggest borage flowers can elevate mood – and indeed, the simple act of adding these pretty flowers to a plate can be uplifting. Use fresh borage flowers in salads or as a decorative garnish for desserts.
Butterfly Blue Pea Flower
The butterfly blue pea flower is perhaps the most visually striking of the blue anthocyanin sources. This pea vine produces intensely blue blossoms. Culinary traditions in Thailand, Malaysia, Burma, and China utilize this stunning flower extensively. Pulut tai tai, a Malaysian sticky rice cake flavoured with coconut and pandan, gets its characteristic blue speckles from these pea flowers. Chor ladda, an intricately shaped Thai dumpling, visually resembles a bright blue flower thanks to this ingredient. In Thailand, the flowers are also used to brew a chilled herbal tea, prized for its refreshing and cooling qualities. The flowers can be used fresh or dried to create a vibrant blue infusion. Dried butterfly blue pea flowers are particularly remarkable, offering a mild, herbal flavour with a subtle hint of cucumber. The only caveat is that their brilliant electric blue colour will transform into a bright purple upon contact with acids.
Other Blue Pigments
Blue Cheese
Stepping slightly outside the plant kingdom, blue cheese owes its distinctive blue not to anthocyanins, but to mold cultures introduced during cheese production. The specific mold varies depending on the type of blue cheese, but all belong to the Penicillium genus – yes, the same family as penicillin (though consuming blue cheese will not cure infections!). The blue colour in cheese is typically deep and stable, not prone to bleeding. When serving blue cheese in cold dishes, try using a wire cheese slicer to create thin sheets. This technique showcases the cheese’s attractive mottled surface far more effectively than simple crumbles.
Pickled Garlic
The appearance of blue in pickled garlic is often unexpected and sometimes alarming. This colour change is a chemical reaction: when raw garlic is pickled, trace amounts of sulfur can react with minuscule amounts of copper present in water or cooking utensils. Initially, the garlic appears normal, but after a few weeks (in some cases, like mine, about two weeks), it can turn blue or green. To prevent this colour change, simply blanch the garlic briefly in boiling water before pickling. The blue colour is due to trace amounts of copper sulfate, not anthocyanins. While the quantity in pickled garlic is harmless, copper sulfate is toxic in larger amounts.
Bluefoot and Blewit Mushrooms
While perhaps more accurately described as purple-blue, Bluefoot and Blewit mushrooms are indeed called “blue” and possess a wonderfully unique and somewhat fantastical appearance. Bluefoot mushrooms are available in specialty stores, though their rarity makes them a premium item. Blewit mushrooms, related to Bluefoots, are even harder to find in some regions. Blewit mushrooms tend to be more uniformly blue-purple, whereas Bluefoot mushrooms exhibit blue primarily at the base. Bluefoot mushrooms offer a rich, woody, and meaty flavour. Like many flavourful mushrooms, their taste intensifies and spreads beautifully when cooked with cream.
