Today, the truffle is one of the world’s most expensive and extravagant foods, reserved for foodies’ special occasions.  They present a musky, earthy, pungent aroma, and are often added as a flavor agent or garnish.  They’re a delicacy on the dish because they’re notoriously difficult to grow and have baffled farmers for decades.  Other crops, such as corn or soy beans, have been monitored, adjusted, and genetically modified extensively to benefit consumers.  You can drive all over the Midwest and see rolling fields of corn and soy beans in excess.  However, truffles are difficult to monitor during their formation since they grow entirely underground near tree roots, and only in very specific soil conditions.

The Outside of a Pèrigord Black Truffle (Photo Credit)
The Inside of a Pèrigord Black Truffle (Photo Credit)

A truffle, by definition, is a fungus that grows completely underground.  In case you’re not familiar with the evolution of fungi, let’s begin with a little chat about the phylogeny of life on Earth.  It may surprise you to learn that you have a common ancestor with a fungus.  That common ancestor lived during the Ectasian period, which dates back between 1.4 and 1.2 billion years ago.  This ancestor was a complex, multicellular organism – just like you, and just like fungi.  Around 1.2 billion years ago, this ancestral species began to evolve in two diverging directions.  One direction lead to the animal branch, from which all humans eventually evolved.  The other branch lead to all the fungi, and eventually to Tuber melanosporum, which produces the Pèrigord black truffle, one of our favorite culinary treats.  Fortunately, we evolved with fancy human brains, meaning we can harvest, cook, and enjoy eating our fungus relatives.

Phylogenetic Tree (We’re the star, and the fungi are next to us.)

The fungus that produces truffles is ectomycorrhizal, meaning that it grows in collaboration with tree roots.  The fungus and the tree (most commonly oak, beech, pine, or hazelnut) form a symbiotic relationship wherein the tree feeds carbohydrates to the fungus, and the fungus gives the tree nutrients that it extracts from the soil.  Like humans, fungi are unable to produce their own sugars, so help from the tree is critical.  (The tree produces sugars from photosynthesis.)  Once the fungus matures and develops into stringy structures under, around, and inside the tree’s roots, a fruiting body – the actual truffle – will begin to grow about a foot underground.  Throughout the truffle’s growth, the entire truffle will remain underground at a depth of around a foot.  Even from underground, the ripe truffle smells quite pungent, allowing animals above ground to find one, dig it up, eat it, and spread the spores – which, like seeds, spur the growth of fungus and truffles in new places.

Tree Roots and Fibrous Fungi in Symbiosis (Photo Credit)

The task of digging up truffles is the one reason truffles are such an expensive delicacy.  While farmers can harvest some crops in bulk from fields, truffles must be located and dug out of the ground individually.  This process is quite labor-intensive and yields a much smaller crop.  Truffles are especially complicated to harvest since they grow entirely underground with no visible identifier above the surface.  The only signal that a truffle is present near a tree root is the smell.  Because of this, humans must rely on some of their animal friends, pigs and dogs, to find them.  Both species’ sense of smell are far superior to that of humans.  Conveniently, pigs are innately drawn to the scent of truffles.  Some researchers think this is because both truffles and male pigs emit androstenol, a musky pheromone.  However, not everyone agrees on this, as this idea has not held up experimentally.  Regardless, pigs are exquisitely good at locating ripe truffles. They often eat the truffles right away after digging them up, however, which can be a problem if someone is trying to harvest and sell them.

Today, many truffle farmers train dogs to find these underground delicacies.  Dogs are friendly, trainable, and will almost always surrender a truffle in favor of praise and a dog biscuit (or two!).  It’s really a great partnership.  Additionally, hounds are naturally inclined to sniff out interesting scents, so it is not difficult to get them excited about finding truffles.  You may find it interesting to know a typical dog has about 300 million olfactory receptors in their nose – that’s 50 times more than an average human has.

A Pig Hunts for Truffles (Photo Credit)

Truffles were initially grown primarily in France, Spain, and Italy.  However, since interest in this expensive delicacy has spread globally, people across the world try to grow truffles.  Growing truffles is a tricky business though, since they are quite picky about their soil conditions and require a rather specific environment. First, the soil must be dry and calcareous.  Calcareous soil is chalky, contains lots of limestone particles, and has a basic pH around 7.5-8.  Second, truffles only grow in and around the roots of oak, hazelnut, pine, poplar, and beech trees.  Third, and most exasperating, is that you can only grow truffles indirectly by planting an orchard of these trees and waiting.  If the fungus is present in the soil, or you purchase and plant tree saplings that have already been inoculated with the fungus, your orchard will begin to grow fungus strings around the roots of the trees over time.  If you maintain the soil properly, and get a pig or train a hound, you should look forward to digging up your first crop of truffles in about 6-10 years.

Have you ever eaten a truffle?  Here are five restaurants in Chicago that currently have truffle products on their menu.  Give them a try!

  1. Daisies Chicago serves Black Truffle Ravioli
  2. Osteria Langhe serves Gnocci with Black Winter Truffles
  3. RPM Italian serves several truffle dishes, including Black Truffle Beef Tartare
  4. Spiaggia has many dishes that incorporate truffles.  You can also taste truffles on their own here.
  5. Siena Tavern uses truffle honey as well as actual truffles in several dishes.
Mixed Wild Mushroom Pasta with Black Truffle Slices (Photo Credit)

*Disclaimer: The listed restaurants did not sponsor this post.


  • Dana Simmons

    Dana Simmons is a Co-Editor-in-Chief of Science Unsealed and holds a Ph.D. in neurobiology from the University of Chicago. She is an active participant in the global SciArt community, and her innovative neuron art has been exhibited around the world. Dana is a medical writer for a Chicago agency that serves pharmaceutical and biotechnology companies. SciArt website: Twitter: @dhsimmons1

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Total Solar Eclipse on April 8, 2024

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On April 8th, 2024, a total solar eclipse will sweep across North America, from Mexico to the Maine-Canadian border. For those who experienced the spectacular solar eclipse of 2017, this one will be similar, crossing the United States from west to east and passing through or near several major metropolitan areas. And while its path is quite different this time, Carbondale, Illinois, a reasonable destination for Chicago-area residents, will once again be on the line of totality.    

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Two women representing the Illinois Science Council at an event.

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