Candy cap and curry milkcap are common names for two closely related species of Lactarius: L. camphoratus and L. rubidus. Additionally, L. rufulus is termed the southern candy cap. Many similar species are known. Candy caps are valued for their highly aromatic qualities and are used as a flavoring.
Taxonomy The candy caps have been placed in various infrageneric groups of Lactarius depending on the author. Bon defined the candy caps and allies as making up the subsection Camphoratini of the section Olentes. Subsection Camphoratini is defined by their similarity in color, odor (with the exception of L. rostratus), and by the presence of macrocystidia on their hymenium. (The other subsection of Olentes, Serifluini, is also aromatic, but have very different aromas from the Camphoratini and are entirely lacking in cystidia.) Bon and later European authors treated all species that were aromatic and had at least a partially epithelial pileipellis as section Olentes, whereas Hesler and Smith and later North American authors treat all species with such a pileipellis (both aromatic and non-aromatic) as the section Thojogali. However, a thorough molecular phylogenetic investigation of Lactarius has yet to be published, and older classification systems of Lactarius are generally not regarded as natural.
Description
Candy caps are small to medium-size mushrooms, with a pileus ranging from 2–7 centimetres (3⁄4–2+3⁄4 in) in diameter, and colored orange-brown to reddish-brown. The pileus shape ranges from broadly convex in young specimens to plane to slightly depressed in older ones; lamellae are attached to subdecurrent. The stipe is 3–6 cm (1+1⁄4–2+1⁄4 in) long. The entire fruiting body can be either firm or fragile and brittle. Like all members of Lactarius, the fruiting body exudes a latex when broken, which in these species is whitish and watery in appearance, and is often compared to whey or nonfat milk. The latex may have little flavor or may be slightly sweet, but should never taste bitter or acrid. These species are particularly distinguishable by their scent, which has been variously compared to maple syrup, camphor, curry, fenugreek, burnt sugar, Malt-O-Meal, or Maggi-Würze. This scent may be quite faint in fresh specimens, but typically becomes quite strong when the fruiting body is dried. Microscopically, they share features typical of Lactarius, including round to slightly ovular spores with distinct amyloid ornamentation and sphaerocysts that are abundant in the pileus and stipe trama, but infrequent in the lamellar trama.
Chemistry
The chemical responsible for the distinct odor of the candy cap was isolated in 2012 by chemical ecologist and natural product chemist William Wood of Humboldt State University, from collections of Lactarius rubidus. The odoriferous compound found in the fresh tissue and latex of the mushroom was found to be quabalactone III, an aromatic lactone. When the tissue and latex is dried, quabalactone III is hydrolyzed into sotolon, an even more powerfully aromatic compound, and one of the main compounds responsible for the aroma of maple syrup, as well as that of curry. The question of what compound was responsible for the odor of candy cap had been under investigation by Wood and various students for a period of 27 years, when a mycology student in a class he was teaching asked what compound was responsible for the mushroom's odor, triggering investigation into the question. Isolation of the compound remained elusive, until solid-phase microextraction was used to extract the volatile compounds, which were then analyzed using gas chromatography–mass spectrometry. Earlier investigation of the aromatic compounds of L. helvus by Rapor, et al. had also yielded sotolon (among a large number of other aromatic compounds), which was identified as giving this species its distinct fenugreek odor. Other important volatile compounds identified included decanoic acid and 2-methylbutyric acid. Analysis of Lactarius camphoratus has shown that it contains 12-hydroxycaryophyllene-4,5-oxide, a caryophyllene compound. However, this was not identified as an aromatic component of this mushroom.
Identification It is possible to mistake other distasteful or toxic species of mushrooms for candy caps or mistakenly include such species in a larger collection of candy caps. Those inexperienced with mushroom identification may mistake any number of "little brown mushrooms" (LBMs) for candy caps, including the deadly galerina (Galerina marginata and allies), which can occur in the same habitat. Candy caps can be distinguished from non-Lactarius species by their brittle stipe, while most other LBMs have a more flexible stipe. It is therefore recommended that candy caps be gathered by hand, breaking the fragile stipe in one's fingers. By this method, LBMs with a cartilaginous stipe will easily be distinguished. Candy caps may also be confused with any of a large number of small, similarly colored species of Lactarius that may be distasteful to downright toxic depending on the species and the number consumed. Candy caps may be distinguished from other Lactarius by the following characteristics:
Odor: Candy caps have a distinctive odor (described above) that should not be present in other species of Lactarius. However, that other species of Lactarius may have different, but also distinctive, odors. Fresh candy caps (especially L. rubidus) may also not have a noticeable odor, limiting the utility of this characteristic. A sweet odor is much more evident after briefly singeing the flesh of a candy cap with a match or lighter, which can be useful for identification. Taste: The flesh and latex of candy caps should always be mild-tasting to somewhat sweet, lacking any hint of bitterness or acridity. Note, however, that there are some species of Lactarius, such as L. luculentus, where the bitterness is subtle and also may not be noticeable for a minute or so after tasting. Latex: The latex of candy caps appears thin and whey-like, like milk that has been mixed with water. This latex does not change color nor does it discolor the flesh of the mushroom. Other species of Lactarius have a distinctly white or colored latex, which in some species discolors the flesh of the mushroom. Pileus: Candy caps never have a zonate pattern of coloration on the surface of the pileus, nor is the pileus ever even slightly viscid.
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