John Miller
The blue milk mushroom, also known as Lactarius indigo, is a distinctive fungus that is easily recognisable by its indigo blue colour and unique appearance. It is a well-known edible species that grows in coniferous forests and oak and pine woods, and is sold in rural markets in China, Guatemala, and Mexico. The blue milk mushroom has a coarse, grainy texture and a slightly bitter or peppery taste. Its colour disappears when cooked, turning grey, and it has a firm flesh that is best prepared by cutting the mushroom into thin slices.
| Characteristics | Values |
|---|---|
| Common Names | Indigo milk cap, Indigo Lactarius, Blue milk mushroom, Blue Lactarius, añil, azul, hongo azul, zuin, zuine, quexque |
| Scientific Name | Lactarius indigo |
| Colour | Indigo blue, becoming paler with age, greenish when bruised or damaged |
| Shape | Cap convex to sunken, with inrolled margin; gills adnate to slightly decurrent; stalk often tapered towards the base |
| Size | Cap diameter: 4-15 cm; stalk thickness: 1-2.5 cm |
| Texture | Initially sticky or slimy, becomes dry with age; firm flesh, coarse and grainy |
| Taste | Slightly bitter or peppery |
| Edibility | Edible, sold in rural markets in China, Guatemala, and Mexico |
| Habitat | Grows on soil in oak and pine woods |
| Spore Colour | Cream |
| Nutritional Content | High in moisture, fat, protein, and dietary fiber compared to other mushroom species |
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What You'll Learn
Habitat and growth
The Lactarius indigo, commonly known as the blue milk mushroom, is a distinctive fungus with a vivid blue colour and a unique growth habit. It is a well-known edible species, often found in rural markets in China, Guatemala, and Mexico. The blue milk mushroom grows scattered or in groups on soil in oak and pine woods, typically from June to November. It is often found under Eastern White Pine trees, where it fruits from mid to late August. The fungus forms a symbiotic relationship with the trees it grows on, increasing the surface area of the roots and their ability to absorb water and nutrients. In return, the tree shares nutrients with the fungus.
The blue milk mushroom develops from a nodule that forms within the underground mycelium, a mass of thread-like fungal cells called hyphae that make up the bulk of the organism. Under the right environmental conditions of temperature, humidity, and nutrient availability, the visible reproductive structures, or fruit bodies, are formed. The cap of the fruit body, measuring between 4–15 cm in diameter, is initially convex and later develops a central depression, becoming more funnel-shaped as the edge of the cap lifts upward. The gills of the mushroom are attached to the stem and are crowded close together, ranging in colour from indigo blue to silvery or grayish blue. The stem is typically 1–2.5 cm thick, with a solid and firm interior that becomes hollow with age.
The blue colour of the Lactarius indigo is due to the presence of (7-isopropenyl-4-methylazulen-1-yl)methyl stearate, an organic derivative of azulene. This compound is biosynthesised from a sesquiterpene similar to matricin, the precursor for chamazulene. The blue colour of the mushroom can be retained through blanching or pickling, although this may sacrifice the depth of flavour that comes from browning in a pan. The mushroom can also be preserved in oil or dried in a dehydrator.
The blue milk mushroom is considered a "second-class" species for consumption in Mexico, with a slightly bitter or peppery taste and a coarse, grainy texture. The firm flesh is best prepared by cutting the mushroom into thin slices. The blue colour disappears when cooked, and the mushroom turns grayish. However, the mushroom can be stewed or marinated to retain its colour.
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Physical characteristics
The Lactarius indigo, commonly known as the blue milk mushroom, is a distinctive fungus with a vivid blue hue. This unique colour is due to the presence of (7-isopropenyl-4-methylazulen-1-yl)methyl stearate, an organic derivative of azulene. The entire mushroom is bluish, with gills that range from indigo blue to greenish-blue. The gills are attached to the stem, either squarely or slightly running down its length, and are crowded close together. The stem is typically 1–2.5 cm thick, with a diameter that may narrow towards the base. Its colour ranges from indigo blue to silvery or grayish blue, and it has a dry, pockmarked texture with irregular circles. The interior of the stem is initially solid and firm but becomes hollow as the mushroom ages. The cap of the mushroom, measuring between 4–15 cm in diameter, is initially convex with an inrolled margin, developing a central depression over time and becoming funnel-shaped as the edge of the cap lifts upward. The cap may have dark blue spots, especially towards the edge, and young caps are sticky to the touch. With age, the cap becomes paler and bruises greenish, and the gills stain blue-green when damaged.
The blue milk mushroom is a well-known edible species, sought after by mushroom enthusiasts and hunters. It grows on soil in oak and pine woods, often scattered or in groups, and is found in regions such as Missouri, Mexico, and Guatemala. The mushroom is mycorrhizal, forming a symbiotic relationship with tree roots and helping to nourish forest trees.
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Taste and edibility
The Lactarius indigo, commonly known as the blue milk mushroom, is a well-known edible species of mushroom. However, opinions vary on its taste and quality. American mycologist David Arora considers it a "superior edible", while a field guide on Kansas fungi rates it as "mediocre in quality". The mushroom may have a slightly bitter or peppery taste and a coarse, grainy texture. The firm flesh is best prepared by cutting the mushroom into thin slices. The distinct blue colour disappears with cooking, and the mushroom turns grey. Due to the granular texture of the flesh, it is not suitable for drying.
The blue milk mushroom is often compared to other wild edible mushroom species such as Amanita rubescens, Boletus frostii, and Ramaria flava. Chemical analysis has shown that L. indigo contains higher levels of moisture, fat, protein, and dietary fibre than the common button mushroom. It also has the highest saturated fatty acids content among the tested species, including a significant amount of stearic acid.
When preparing the blue milk mushroom, it is important to note that the colour will fade during cooking. To retain the vibrant blue colour, some suggest blanching or pickling the mushrooms. While this method preserves the colour, it sacrifices the depth of flavour achieved by browning the mushrooms in a pan. One successful method for preserving the colour is stewing the mushrooms and keeping them moist, without letting them touch the bare pan. This can be followed by marinating with herbs, garlic, and vinegar. Pickling or preserving in salt brine is another effective way to maintain the blue colour. Additionally, blanching the mushrooms quickly in salted water can help retain the colour before marinating with an acidic ingredient like lemon juice or vinegar.
The blue milk mushroom is safe to consume raw and has a crisp texture similar to an apple. It is commonly grilled, used in soups, or dried and preserved. However, it is important to exercise caution when consuming wild mushrooms, as some species within the Lactarius genus are edible but poisonous.
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Nutritional content
The blue milk mushroom, or Lactarius indigo, is an edible species of agaric fungus in the family Russulaceae. It has a distinctive vibrant blue colour, which comes from an organic compound called methyl stearate, which is unique to this species. The blue colour disappears when cooked, turning the mushroom grey.
Blue milk mushrooms have a similar texture to portobello mushrooms, described as coarse and grainy, and a slightly bitter or peppery taste. They have a firm flesh, which is best prepared by cutting the mushroom into thin slices. The blue milk mushroom contains moisture at 951 mg/g of mushroom, fat at 4.3 mg/g, protein at 13.4 mg/g, and dietary fibre at 18.7 mg/g. This is much higher than the common button mushroom, which contains 6.6 mg/g of dietary fibre.
Blue milk mushrooms are high in saturated fatty acids, including stearic acid, which makes up 32.1 mg/g of the total free fatty acid content. They also contain indigo blue gills, which stain green when damaged or cooked. The mushrooms have a long fruiting season, appearing in late spring and continuing through late fall.
Blue milk mushrooms are often sold in China and Central America, and are used for a variety of purposes, including as a basis for fluorescent pigments and dyes.
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Similar species
While the blue colour of the Lactarius indigo mushroom is quite distinctive, there are a few similar species. Firstly, dangerous Cortinarius mushrooms have a somewhat comparable colour, although they are more purple in appearance. Cortinarius mushrooms also have a webby veil over their gills, which the indigo milk cap lacks. Blewits (Clitocybe nuda) are also coloured, but they are predominantly grey or purple. However, they are edible and considered tasty.
In terms of habitat, milk cap mushrooms tend to grow in the same places as indigo milk caps. Saffron milk caps, for example, may be found in the same locations as indigo milk caps, so it is worth checking back during the season to see the different types that fruit. Milk caps are often found in coniferous forests, so they may be found among pine needles.
The Lactarius genus contains several other edible species, although many are poisonous. Lactarius piperatus, for example, has a peppery flavour, while L. deceptivus causes a lingering burning sensation in the mouth. Lactarius indigo is considered a superior edible by some, such as American mycologist David Arora, but others, like a field guide on Kansas fungi, rate it as mediocre in quality.
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Frequently asked questions
A blue milk mushroom, or Lactarius indigo, is an edible mushroom species that has a distinctive blue colour and is known by several names, including indigo milk cap, indigo Lactarius, and blue Lactarius.
Blue milk mushrooms have a cap that is initially convex and later develops a central depression, becoming more funnel-shaped as the edge of the cap lifts upward. The gills are indigo blue, becoming paler with age or staining green when damaged. The stem is thick and the same diameter as the cap, with a solid and firm interior that becomes hollow with age.
Blue milk mushrooms grow in coniferous forests, scattered or in groups, on soil in oak and pine woods. They are often found under Eastern White Pine trees and typically fruit from July to November.
Yes, blue milk mushrooms are edible and are sold in rural markets in China, Guatemala, and Mexico. However, opinions vary on their taste and quality, with some considering them a "superior edible" while others rate them as "mediocre". They may have a slightly bitter or peppery taste and a coarse, grainy texture. The blue colour disappears when cooked, turning grey.
