Are mushrooms “kosher”?
On occasion, more often than not in the independent sectors of the Messianic community and/or Hebrew/Hebraic Roots world, one will hear a claim made from time to time that mushrooms, and by association various other fungi, are non-kosher. Much of this relates to how mushrooms reproduce. Yet, one need not go too far to realize that mushrooms are a feature of traditional Jewish cooking. This means that at one point in history, Jewish religious authorities decided that mushrooms, even if they do not bear seed (cf. Genesis 1:29) in the more customary sense, may be considered a food product eligible for consumption.
You will find that most Messianic people do consider mushrooms to be kosher, although like any food product mushrooms should be thoroughly washed before being eaten. There are also considerable dangers associated with picking wild mushrooms, as many mushrooms are poisonous. So sticking with commercially processed mushrooms should be regarded as the safest option for most people.
The following entry is excerpted from the Orthodox Jewish website Kashrut.com, in an article entitled “A Fungible Feast, Mushrooms in Halacha” by Rabbi Zushe Blech. Even with some Orthodox Jewish customs and traditions interwoven into these remarks, what is communicated should be viewed as substantial enough for Messianic people to recognize that mushrooms are considered kosher by Jewish authorities:
There is a category of food that seems to defy classification. It is not fruit nor vegetable nor animal, yet exhibits the characteristics of them all. As every child studies the laws of Berachos [blessing], he quickly learns that there are two basic blessings for plants. The Beracha for foods that grow on trees is generally Borei Pri Haetz (Blessed the creator of the fruit of the tree) whereas that for foods that grow on the ground is Borei Pri Ho Adama (Blessed the creator of the fruit of the ground). One quickly learns the seeming incongruities associated with these Berachos (a banana is considered the fruit of the ground while a raspberry may be considered a fruit of the tree), but one food the mushroom seems to defy conventional classification. The Talmud (Berachos 40b) states that although mushrooms grow on the ground, the proper Beracha is nonetheless Shehakol, the general Beracha for foods that are not plants. The Talmud explains that although mushrooms do indeed grow on the ground, they are exceptional in that they do not derive their primary nutrition from the soil, as do other plants. [Interestingly, the Aruch Hashulchan (204:5), among others, holds that if one made a mistake and recited Ho Adama on mushrooms, it would be acceptable, since the Talmud does consider mushrooms to be Gidulei Karka (growths of the ground), although they do not derive their sustenance from it.] The unique status of mushrooms is not limited to their Beracha, however. Once reserved to Egyptian royalty, mushrooms have become a popular food with interesting Halachic ramifications.
Before we can discuss the Halachic applications of mushrooms as a food, we must first establish what they are. The mushroom is actually only a small, visible part of a much larger fungus. Unlike plants that rely on photosynthesis to produce their food, fungi act as parasites, deriving their nutrition from decaying organic material. Although we see mushrooms popping up from the ground, they are but the tip of the fungal iceberg. The main part of the fungus is under the ground in the form of white mycelia, which can grow into huge organisms (one huge fungus growing underground in Oregon that reputedly covers 2200 acres, and is thought to be the largest known single living organism in the world!).
The mushroom that we observe and eat is actually the fruiting body of the fungus, which the fungus sprouts as spore-producing appendages to spread its spores; the vegetative portion of the fungus remains underground. The most common mushroom of this type grown commercially is the species called Agaricus bisporus, which produces the white button mushroom. The popular Portobello mushroom, with a stronger meaty flavor, is actually the same mushroom picked at its fully mature stage. It is interesting to note that until about ten years ago, these overgrown mushrooms were considered a troublesome waste until someone realized that they served as an excellent meat substitute…
The use of wild mushrooms as food…is quite ancient and poses no inherent Kashrus concern for either year round use or for Pesach. Commercial production, however, is of rather recent vintage, beginning in France in the early 1700s and making its way to the United States in 1880. The key to successful mushroom production is finding an ample supply of decaying material (compost) to be used as the mushroom bedding, and finding a way to inoculate this bedding with the desired fungal spores. The compost used in mushroom production is generally made by mixing a variety of less than savory ingredients [like] horse manure, wheat or rye straw, peat moss, used horse bedding straw, chicken manure, cottonseed or canola meal, grape crushings from wineries, soybean meal, potash, gypsum, urea, ammonium nitrate, and lime. The composting process ensures that these materials are hygienic and safe, and since all of this material is by definition decomposed, it poses no Kashrus concerns.
The next step involves the inoculation of the bedding with spawn the fungal spores that actually begin the growth of the fungus in the bedding. As is the case with the commercial propagation of other microorganisms, a culture of spores (spawn) is prepared and grown under specially controlled conditions to ensure that just the right strain of fungus is isolated. As the spawn develops, it is allowed to colonize kernels of moist rye or millet, which are then seeded into the bedding to begin the growth of the main fungus. Moist rye, one of the five major grains, would most certainly pose a concern of Chometz, and some have therefore cautioned against using such mushrooms on Pesach. On the other hand, most authorities do not consider this to be a problem. First, the grain is not actually the seed for the mushroom, but merely a carrier of the spawn. Second, the grain itself decomposes and is rendered inedible. In addition, one should note that all grain comes from sprouted seeds that are Chometz, yet the resulting new grain is certainly not considered Chometz when it is grown before Pesach. [There is indeed a question about the status of grain that grew from Chometz seeds that were planted on Pesach (see Chasam Sofer O.C. 104). There is no question, however, about grain that was grown before Pesach.]
Other types of mushroom-producing fungi grow in decaying wood. Shiitake mushrooms (from the Japanese shi = oak and take = mushroom) were originally grown on oak logs, but today are grown on oak sawdust. The flavor of these types of mushrooms depends on the type of wood on which they grow.
Not all edible fungal fruiting bodies, however, mushroom from the ground. One of the most prized items in the gastronomic world, the truffle grows underground and feeds on nutrients supplied by the roots of trees. These pungent and flavorful bits of fungus were noted at the times of the Talmud, where edible fungi were referred to as Kemehin and Pitriyos. Rabbeinu Yona explains Kemehin to mean those types that grow underground (truffles), while Pitriyos are the mushrooms that often grow on wood (and presumably on the ground). [The truffle was indeed so valued that a chocolate confection was named after it. The chocolate truffle actually contains no real truffle. Its shape a round ball of chocolate dusted with cocoa was designed to look like a dug up truffle, evoking the aura of delectable fungus after which it was named.]
Another Kashrus issue that has been the subject of discussion is the possible need to check mushrooms for insect infestation. Rav Moshe Feinstein ztl (Igros Moshe Y.D.II,25) notes that in Europe, mushrooms were known to be infested and there was therefore a requirement that they be checked. In North America, however, he argues that such infestation is not common and mushrooms are not considered to be subject of a significant concern in this regard. Rav Moshe does suggest, however, that one should still check mushrooms to ensure that the situation has not changed, and it is interesting to observe that his prescient injunction has recently been vindicated. Much of the canned mushrooms sold around the world are currently produced in China, and it seems that productions of mushrooms under otherwise reliable Hashgacha were found to be heavily infested.
 Rabbi Zushe Blech. (2002). A Fungible Feast, Mushrooms in Halacha. MK Vaad News & Views. Retrieved 06 January, 2014, from <http://kashrut.com>.