Fungi are weird, but they are delicious.

Got a question you want answered in a hurry? Checkout the FAQ.

We sometimes forget just how different fungi are. They’re not quite plants and they’re definitely not animals. Its hard to know what to make of them. Fungi are their own thing.

We generally think of mushrooms when we think of fungi, but they are much more than that. The largest organism on earth is a fungus covering 3.4 square miles in Oregon and it has existed for at least 2,500 years.

Fungi can be pathogens; they give us athletes foot for example. If you are an insect, especially if you are an ant, fungi can infect your brain and enslave you in a zombie army. The Last of Us is a documentary if you’re an ant.

Humans have used fungi for thousands of years. We’ve always believed in their medicinal qualities. Otzi the Iceman had two types of fungi in his pocket that he was probably using as some type of medicine. More recently, magic mushrooms have been touted as a possible treatment for dementia.

And, of course, they have always been a source of food. But don’t eat the wrong mushroom or you’ll die a painful death. Just like the Roman emperor Claudius who was fed poison mushrooms by his wife Agrippina, clearing the way for her son Nero to become emperor.

Yes, fungi are weird, but they are delicious weird, so let’s have a look at the science behind fungi as a food.

What Are Fungi? (And Why They Aren’t Plants or Animals)

Fungi make up an entire biological kingdom of their own. Genetically they are more related to animals and, like animals, they break down organic matter to survive. They don’t photosynthesise like plants. On the other hand, like plants, they don’t tend to move around a lot, and they have a cell wall, but theirs is made of chitin not cellulose.

When we think of fungi as food we tend to think of mushrooms. But mushrooms aren’t actually the fungus. They are what’s known as fruiting bodies, ephemeral structures that disperse spores that will ultimately grow into new fungi.

Mushrooms are the reproductive organ of the fungus.

Most multicellular fungi are made up of fine, branching thread-like structures called hyphae. These threads form a matted mass called a mycelium. The mycelium can be microscopic or span acres, like in Oregon.

To feed itself the mycelium secretes digestive enzymes that break down organic matter in its immediate environment into smaller molecules that can be easily absorbed as nutrients.

There are about 1000 species of edible fungi and in most cases, we only eat the mushrooms of the fungus, not the mycelium. So mushrooms, you could say, are a little bit like prairie oysters.

Cultivated vs. Wild Fungi

Some fungi grow on decomposing plant material, either dead vegetation or the dung of plant eating animals. This group includes well known mushrooms like button and shiitake mushrooms.

Other fungi parasitise, or live symbiotically on, other organisms. These organisms are usually plants. Ustilago maydis, the fungi that produces corn smut for example, is a parasite of corn.

The fungi that produce truffles and chanterelles also have a symbiotic relationship with plants. They grow on the roots of trees and share nutrients they gather from the soil in exchange for sugars produced by the trees.

In general, fungi that grow on decaying matter are easy to cultivate. Just get a pile of manure and you’ll soon have button mushrooms.

Fungi that form relationships with plants are more difficult. Truffles, for example, are very difficult to cultivate as they require specific trees to grow on and they are very picky about the soil and climate.

It can take many years before cultivated truffles can be harvested and even then, yields are uncertain.

Because of this mushrooms like truffles, chanterelles and morels are still mostly wild-harvested rather than cultivated and this is why they can be so expensive.

Chitin vs. Cellulose: Thermal Stability in the Kitchen

Something that has a definite effect on how we deal with mushrooms in the kitchen is the fungal cell wall. Like plants, fungal cells a surrounded by a tough but flexible wall, but where plant cell walls are made of cellulose, fungal cell walls are made of chitin.

Metric / Property	Plant Cell Walls (Cellulose)	Fungal Cell Walls (Chitin)
Primary Building Block	Glucose polymers	N-acetylglucosamine polymers
Bonding Strength	Standard hydrogen bonding	Enhanced hydrogen bonding via acetyl amine groups
Thermal Breakdown Temperature	~260°C (500°F)	~300°C (572°F)
Culinary Texture Result	Softens and turns mushy with long cooking	Retains firm, springy structure under high heat

Chitin is a lot harder than cellulose, which makes fungal cell walls a lot stronger than those found in plants. Chitin is the same substance that insects use to make their exoskeletons.

If you compare the shell of an insect to, say, a stick of wilted celery you can see how much harder chitin is than cellulose.

Lobsters also use chitin to make their shells, though in this case they combine it with calcium carbonate to make them even harder, but you get the idea, chitin is hard.

Give me the chemistry

Chitin, like cellulose, is a polysaccharide but while cellulose is made up of glucose monomers chitin is made up of 2-(acetylamino)-2-deoxy-D-glucose. Which in English means a glucose molecule with one OH group replaced by an acetyl amine group. OK, that’s not much better English but what it means is that chitin is able to form more hydrogen bonds which makes structures made of chitin stronger, or harder, than those made of cellulose.

How to Cook Mushrooms Perfectly: The Science of Dry-Searing

Mushrooms exist to distribute spores that will make new fungi. To facilitate this, they have an extensive system of pipes that allow spores produced in the interior of the mushroom access to the surface for dispersal.

Mushrooms are also 90-95% water and this, combined with chitin cell walls, pipes and lots of water, makes mushrooms very much like sponges.

Because of this you need to be careful when cooking mushrooms. If you start cooking them in a pan with oil, they will absorb a lot of that oil before they are cooked, making them greasy. Then, when they get hot enough, they will release all their water into your dish, potentially making it soggy.

The best way to cook mushrooms is to start them off on a dry heat, or maybe with a little bit of water, so they don’t absorb any oil or fat. Then, when they have released their water and it has cooked off, add your oil or fat.

By the time the water has evaporated some of the internal structure of the mushroom will have collapsed and they will absorb less of the cooking fat.

If you do all this over a relatively high heat you’ll also avoid stewing your mushrooms in their own water and you’ll encourage some flavourful Maillard reactions.

On the plus side, chitin makes it difficult to overcook a mushroom. Chitin is stable up to about 300$\degree$C, a temperature you’ll probably only ever reach if stir frying and which you’ll never reach if braising or roasting. So mushrooms will retain their shape and texture no matter how long, within reason, you cook them.

The Chemistry of Mushroom Flavour: Umami, GMP, and Aroma Compounds

Mushrooms have always been used for the savoury flavours they bring to a dish. In fact, they are probably one of the few unprocessed foods, along with tomatoes and some seaweeds, that can bring a lot of umami to a dish on their own.

Synergistic Umami: Glutamates and Nucleotides

Mushrooms get their savoury flavour because they contain large amounts of glutamic acid, the same molecule that gives monosodium glutamate (MSG) its intense flavour.

Mushrooms also contain a molecule called guanine monophosphate (GMP). GMP most likely targets the same receptor as MSG and is able to enhance the umami flavour of all that glutamic acid.

Shiitake mushrooms, in particular, have an abundance of GMP, which is what makes them such potent umami bombs.

Octenol and Lenthionine: The Secret Behind Fungal Aromas

Apart from the umami, different species of fungus can have a whole range of different flavours. Laetiporus sulphureus, known as the ‘Chicken of the Woods’ mushroom, apparently tastes just like chicken.

Porcini mushrooms provide a slightly sweet and nutty flavour, Lion’s mane mushrooms mimic the flavour of crab or lobster and can be used as a seafood alternative, and beech mushrooms bring a nutty note to a dish (if you want to investigate this more see here).

Mushrooms are also well stocked with molecules that contribute to an attractive aroma.

When damaged mushrooms produce octenol from polyunsaturated fats which contributes to the typical aroma of fresh mushrooms. Somewhat disturbingly, octenol is also a component of human breath and sweat.

The distinct aroma of shiitake mushrooms is caused by a molecule called lenthionine. This molecule is a cyclic oligosulfide, that contains large amounts of sulphur.

Sulphur is common constituent in molecules that flavour our food. Molecules containing sulphur, such as dimethyl sulphide and dimethyl disulphide, also contribute to the pleasant flavour of truffles. Though, as hydrogen disulfide, sulphur is also responsible for the smell of rotten eggs.

Why Dried Mushrooms Can Taste Better Than Fresh Mushrooms

Even after they are harvested, mushrooms are still metabolically active. That is, enzymes that produce flavour and aroma compounds are still active.

If cooked fresh and at high heat, these enzymes don’t have a lot of time to do their thing. But when slowly dried more flavour molecules will be produced as enzymatic activity is retained over a longer period of time.

The drying process also results in Maillard reactions, which we almost always want, and the evaporation of water concentrates the flavour.

Drying mushrooms is thus not only a convenient way to preserve and transport mushrooms but also a very effective way to enhance their flavour.

Edible Molds

Molds are fungi that don’t develop mushrooms, they release spores directly from their mycelium.

We normally encounter molds on bathroom tiles we haven’t cleaned for a while or on old cheese. But we do encounter them in our food sometimes.

My favourite food-related mold, because it makes a delicious wine, is Botrytis cinerea. This fungi is usually a pest that infects and forms a grey mold over many fruits and vegetables.

But, if used in a controlled way during wine production, the water loss from the grapes caused by the infection concentrates the sugars. This produces a very sweet wine but one that is also quite acidic, giving it a zest that balances out the sweetness.

Sauternes, from France, are the classic example of a botrytis wine, though Trockenbeerenauslese, from Germany and Austria, and Tokaji Aszú, from Hungary, are other examples.

We don’t actually consume Botrytis, but there are some examples of edible molds. Huitlacoche, also known as corn smut, is caused by a mold, Ustilago maydis, that infects corn.

The infection causes the kernels to swell up into a structure known as a ‘gall’ which is a combination of swollen plant cells, the hyphae of the mold and a bunch of blue-black spores.

When cooked the galls have the consistency of a mushroom and a sweet, smoky flavour. It is a delicacy in Mexico where it can be incorporated into almost any dish, often as a meat substitute, and has been eaten since Aztec times.

A fungus from the same genus, Ustilago esculenta, does something similar to an Asian wild rice species, Zizania latifolia, where it forms galls in the stem. These galls can be harvested and are a delicacy in China, Japan and other parts of Asia.

You Probably Shouldn’t Go Mushroom Picking Yourself

A lot of organisms object when other organisms start eating their reproductive organs. Some plants want animals to eat their fruit, but other organisms go to great lengths to stop this happening.

We saw this with chillies, for example, and there are a lot of poisonous fruits that are designed to deter us from eating them.

Fungi are no different. Fungi make mushrooms to reproduce not to flavour our pasta dishes.

For this reason some mushrooms produce molecules that are designed to stop other organisms from eating them. A lot of these molecules are quite effective at deterring mammals from eating them and, in humans, they can cause serious illness or death.

So unless you really, really know what you are doing don’t go mushroom picking yourself. Mushrooms come in all shapes and sizes but some deadly species look a lot like edible species.

Agaricus xanthodermus is one mushroom that causes a lot of poisoning cases because it resembles other, edible mushrooms, and there are more like this.

Conclusion

Focusing on food, I’ve really only scrapped the surface of what we know about fungi. Their sex life, for example, makes for some interesting reading. I’ve also not talked much about yeast, another fungi that is incredibly important for a whole bunch of our foods, in particular beer and wine.

So, no doubt I’ll touch on fungi again in later posts but for now we can thank the weird and wonderful world of fungi for contributing to some of our favourite foods.