- Similar Species
- Preserving (Drying or Freezing)
- Recipe Suggestions
Lactarius indigo, commonly known as the indigo milk cap, the indigo (or blue) lactarius, or the blue milk mushroom, is a species of agaric fungus in the family Russulaceae. A widely distributed species, it grows naturally in eastern North America, East Asia, and Central America; it has also been reported in southern France. L. indigo grows on the ground in both deciduous and coniferous forests, where it forms mycorrhizal associations with a broad range of trees. The fruit body color ranges from dark blue in fresh specimens to pale blue-gray in older ones. The milk, or latex, that oozes when the mushroom tissue is cut or broken — a feature common to all members of the genus Lactarius — is also indigo blue, but slowly turns green upon exposure to air. The cap has a diameter of 5 to 15 cm (2 to 6 in), and the stem is 2 to 8 cm (0.8 to 3 in) tall and 1 to 2.5 cm (0.4 to 1.0 in) thick. It is an edible mushroom, and is sold in rural markets in China, Guatemala, and Mexico.
Like many other mushrooms, L. indigo develops from a nodule, or pinhead, that forms within the underground mycelium, a mass of threadlike fungal cells called hyphae that make up the bulk of the organism. Under appropriate environmental conditions of temperature, humidity, and nutrient availability, the visible reproductive structures (fruit bodies) are formed. The cap of the fruit body, measuring between 5 and 15 cm (2.0 and 5.9 in) in diameter, is initially convex and later develops a central depression; in age it becomes even more deeply depressed, becoming somewhat funnel-shaped as the edge of the cap lifts upward. The margin of the cap is rolled inwards when young, but unrolls and elevates as it matures. The cap surface is indigo blue when fresh, but fades to a paler grayish- or silvery-blue, sometimes with greenish splotches. It is often zonate: marked with concentric lines that form alternating pale and darker zones, and the cap may have dark blue spots, especially towards the edge. Young caps are sticky to the touch.
The flesh is pallid to bluish in color, slowly turning greenish after being exposed to air; its taste is mild to slightly acrid. The flesh of the entire mushroom is brittle, and the stem, if bent sufficiently, will snap open cleanly. The latex exuded from injured tissue is indigo blue, and stains the wounded tissue greenish; like the flesh, the latex has a mild taste. Lactarius indigo is noted for not producing as much latex as other Lactarius species, and older specimens in particular may be too dried out to produce any latex.
The gills of the mushroom range from adnate (squarely attached to the stem) to slightly decurrent (running down the length of the stem), and crowded close together. Their color is an indigo blue, becoming paler with age or staining green with damage. The stem is 2–6 cm (0.8–2.4 in) tall by 1–2.5 cm (0.4–1.0 in) thick, and the same diameter throughout or sometimes narrowed at base. Its color is indigo blue to silvery- or grayish blue. The interior of the stem is solid and firm initially, but develops a hollow with age. Like the cap, it is initially sticky or slimy to the touch when young, but soon dries out. Its attachment to the cap is usually in a central position, although it may also be off-center. Fruit bodies of L. indigo have no distinguishable odor.
L. indigo is distributed throughout southern and eastern North America but is most common along the Gulf Coast, Mexico, and Guatemala. Its frequency of appearance in the Appalachian Mountains of the United States has been described as “occasional to locally common”. Mycologist David Arora notes that in the United States, the species is found with ponderosa pine in Arizona, but is absent in California’s ponderosa pine forests. It has also been collected from China, India, Guatemala, Costa Rica (in forests dominated by oak), and as its southernmost distribution in the Humboldt oak cloud forests of Colombia. In Europe, it has so far only been found in southern France. A study on the seasonal appearance of fruiting bodies in the subtropical forests of Xalapa, Mexico, confirmed that maximal production coincided with the rainy season between June and September.
L. indigo is a mycorrhizal fungus, and as such, establishes a mutualistic relationship with the roots of certain trees (“hosts”), in which the fungi exchange minerals and amino acids extracted from the soil for fixed carbon from the host. The subterranean hyphae of the fungus grow a sheath of tissue around the rootlets of a broad range of tree species, forming so-called ectomycorrhizae—an intimate association that is especially beneficial to the host, as the fungus produces enzymes that mineralize organic compounds and facilitate the transfer of nutrients to the tree.
Reflecting their close relationships with trees, the fruit bodies of L. indigo are typically found growing on the ground, scattered or in groups, in both deciduous and coniferous forests. They are also commonly found in floodplain areas that have been recently submerged. In Mexico, associations have been noted with Mexican alder, American Hornbeam, American Hophornbeam, and Liquidambar macrophylla, while in Guatemala the mushroom associates with smooth-bark Mexican pine and other pine and oak species. In Costa Rica, the species forms associations with several native oaks of the genus Quercus. Under controlled laboratory conditions, L. indigo was shown to be able to form ectomycorrhizal associations with the neotropical pine species Mexican white pine, Hartweg’s pine, Mexican yellow pine, smooth-bark Mexican pine, and the Eurasian pines Aleppo pine, European black pine, maritime pine, and Scots pine.
The characteristic blue color of the fruiting body and the latex make this species easily recognizable.
L. indigo var. diminutivus (below) (the “smaller indigo milk cap”) is a smaller variant of the mushroom, with a cap diameter between 3 and 7 cm (1.2 and 2.8 in), and a stem 1.5–4.0 cm (0.6–1.6 in) long and 0.3–1.0 cm (0.1–0.4 in) thick. It is often seen in Virginia. Hesler and Smith, who first described the variant based on specimens found in Brazoria County, Texas, described its typical habitat as “along [the] sides of a muddy ditch under grasses and weeds, [with] loblolly pine nearby”.
Other Lactarius species with some blue color include the “silver-blue milky” (L. paradoxus)(below), found in eastern North America, which has a grayish-blue cap when young, but it has reddish-brown to purple-brown latex and gills.
L. chelidonium has a yellowish to dingy yellow-brown to bluish-gray cap and yellowish to brown latex. L. quieticolor has blue-colored flesh in the cap and orange to red-orange flesh in the base of the stem. Although the blue discoloration of L. indigo is thought to be rare in the genus Lactarius, in 2007 five new species were reported from Peninsular Malaysia with bluing latex or flesh, including L. cyanescens, L. lazulinus, L. mirabilis, and two species still unnamed.
Although L. indigo is a well-known edible species, opinions vary on its desirability. For example, American mycologist David Arora considers it a “superior edible”, while a field guide on Kansas fungi rates it as “mediocre in quality”. It may have a slightly bitter, or peppery taste, and has a coarse, grainy texture. The firm flesh is best prepared by cutting the mushroom in thin slices. The blue color disappears with cooking, and the mushroom becomes grayish. Because of the granular texture of the flesh, it does not lend itself well to drying. Specimens producing copious quantities of milk may be used to add color to marinades.
In Mexico, individuals harvest the wild mushrooms for sale at farmers’ markets, typically from June to November; they are considered a “second class” species for consumption. L. indigo is also sold in Guatemalan markets from May to October. It is one of 13 Lactarius species sold at rural markets in Yunnan in southwestern China.
Preserving (Drying or Freezing):
They dry well but loose their color. I have made blue Alfredo sauce and froze it for later use… They can be sliced and dried in a dehydrator, and will make a good stock or powder, and young ones make very good pickles. I don’t really like freezing milkcap mushrooms unless I’m making duxelles, and I haven’t ever even found a patch so saturated with these that I would want to make a concentrated preserve like duxelles with them.
Another interesting way to preserve them is not one you eat. Most mushrooms when combined with a mordant can create a colorful dye. So if you want a funky blue dye for something, do a little research and try your hand at it.
What Do Indigo Milk Caps Taste Like?
The flavor of Indigo Milk Caps is supposed to vary more than other mushrooms, depending on the trees they’re associating with, the soil and other aspects of their growing environment. Last year, we cooked a small batch whose flavor ended up being too peppery to finish. However, the patch we found growing in a grove of beech trees on our mushroom hike last night met the descriptions we’ve read from other mushroom enthusiasts: mild, sweet and nutty with a hint of cracked pepper on the finish.
Indigo Milk Cap Recipe:
There’s no right or wrong way to cook a mushroom, Indigo Milk Caps included. During our hike, we also found two beautiful chicken of the woods (Laetiporus cincinnatus) mushrooms, that have the exact taste and texture of chicken. We’d planned to fry these up as “chicken fingers” to be dipped into a homemade barbecue sauce we’d made with some of our heirloom tomatoes. So, we decided to go ahead and fry up our Indigo Milk Caps at the same time. It turned out to be a great decision – they were delicious!
So we thought we’d share our indigo milk cap recipe in case any of you other mushroom enthusiasts out there were searching for a recipe to try with your indigos:
- 1 cup flour (organic all purpose) for frying mix + ½ cup for “dredging” your mushrooms (explained in instructions)
- ½ teaspoon baking powder
- ½ teaspoon fine ground sea salt
- ½ teaspoon smoked paprika + ½ teaspoon regular paprika
- ½ teaspoon onion powder
- 1 teaspoon garlic powder
- dash of chili powder
- dash of fresh ground black pepper
- ⅛ teaspoon mustard powder
- 1 large egg (we use duck eggs)
- ⅓ cup milk (we use organic whole or raw milk)
- enough organic sunflower oil or other frying oil to cover your mushrooms in whatever pan you’re using (we use a flat-bottomed wok)
- 5 big lactarius indigo mushroom caps or 10 small mushroom caps
- Chop mushrooms into the desirable sized chunks. We quarter or half them.
- Put ½ cup of flour in a medium sized bowl. This is your “dredging” bowl. You’ll want to get a light dusting of flower on the entire outer surface of each mushroom before you dip in the milk/egg mixture.
- Add your egg and milk into another mixing bowl, and whisk together. You’ll dip your dredged mushrooms into your egg/milk mixture before placing them in your frying mix.
- Prepare your frying mix by putting all dry ingredients (flour, spices, etc) into a large bowl. Whisk them together until evenly blended. Once your mushrooms have been: 1) dredged, and 2) dipped in your egg/milk mixture, you’ll drop them into the big bowl of dry ingredients and cover them evenly.
- Once uniformly covered with fry mix, shake off any extra fry mix. We like to place them on a drying rack on top of a cookie sheet until we’re ready to put them in the fryer (you can just use a plate if you’d prefer).
- Heat your cooking oil. Our stove top doesn’t cook particularly hot or cold, so we put it on about 4.5. You’ll know your oil is hot enough when you drop a bit of flour in and it starts sizzling.
- Go ahead and get a drying/cooling sheet ready before you start frying your mushrooms. We like to use a cookie sheet with a drying rack on top. On top of the drying rack, we put down paper towels to soak up any extra oil.
- Next start frying your mushrooms to golden-brown and crispy perfection. It should only take about 4-5 minutes to cook each mushroom if the oil is in the ideal temperature range.
Serve and enjoy!
Note: Lactarius indigos will lose some of their blue color when cooked, turning grayish-blue. When fried, they’re wonderful served straight or with a bit of sauce (we dipped some in a homemade tomato-based bbq sauce).