The Reidsdale truffle farmer bought his degraded farmland three decades ago, hoping to use his background as a forester to restore the soil to how it was before Europeans arrived.

"It's a world first," Mr Marshall said. "We've been experimenting with about 220 different species of oak trees."

The French truffles were grown under a Japanese oak.

"We're the first people in the world to handle a Japanese-French truffle," Mr Marshall said.

Even the chef for the Japanese embassy in Canberra and his wife visited to sample the truffles.

Mr Marshall's achievement comes as the Canberra region's Truffle Festival begins this weekend. The festival is estimated to bring about $8 million in tourism dollars to the region, according to a 2018 study from Central Queensland University.

Festival president Damian Robinson, a truffle farmer himself, said it was a massive drawcard for the region and attracted people from across the globe.

"The Canberra region's not a big producer but the quality of truffles that come from this region are arguably the best in the world because of the incredible cold climate," Mr Robinson said.

"The frosts in winter tend to mature the truffle where the aroma is sensational."

But what is a truffle? Mr Marshall said truffles were a type of fungus - a mycorrhizal fungi - that attach themselves to the roots on inoculated trees.

The truffles send out little roots - mycelia - to bring more water and nutrients to the tree, which in turn generate sugars from photosynthesis to feed the truffles.

"It's a complete partnership," Mr Marshall said. "The trees are healthier. The truffles eat more."

But the truffles themselves want to be dug up by animals so they can spread their spores through animal droppings.

"Or the whiskers. Some of the truffles are designed that when the animal eats them the spores get on their whiskers," Mr Marshall said.

"They're a living creature. They're one of the very few food stuffs on Earth that want to be eaten."

Truffle farming isn't for the faint-hearted. Mr Marshall said he spent 10 years fixing the soil on his 600 acres of property, 10 years planting and growing trees, then 10 years growing the truffles.

Mr Marshall said the soil in Reidsdale used to be so soft that white farmers complained because their horses would sink through it.

After 150 years of heavy cattle and sheep, the soil became extremely compacted.

"The soil is so ceramic now, so flattened and baked, that it can't accept rain," Mr Marshall said.

It took Mr Marshall 10 years of tilling his 600 acres with a special Yeomans plow - an Australian invention - to restore the soil to its pre-European softness.

Even then, he was using his specialised Italian tractor which exerts less pressure on the ground underneath. But it requires a lot of attention to constantly manipulate gears to manage the downward pressure.

"That's me, up and down, up and down, for hundreds and hundreds of hours," he said.

But thanks to all that hard work, Mr Marshall's truffles thrive.

"It's very hard work and it's certainly not to be considered as a quiet retirement venture."

Before he and his plow came along, Mr Marshall said the native marsupials like the bettong helped keep the soil soft.

"They're gone now because the foxes and the cats killed them," Mr Marshall said.

He said a bettong could till about six to 10 kilos of soil a year, with about 20 of them over a small parcel of land a substitute for Mr Marshall's plow.

But it was also the Indigenous people in the area who made use of the soil: farming bush tucker like yam daisies.

The soft soil also helped the truffles retain a smoother shape.

"If you get a lot of crevices in truffles you get a lot of dirt inside them which is very bad for biosecurity," he said.

Mr Marshall said he started all the work because he wanted to prove you could fix Australian country side. Now, he sits on about 600 acres of restored land with 20 to 30 acres of that now wetland.

Is it worth it? Depending on the type of truffle, Mr Marshall can fetch $1000 to $2000 per kilo and is aiming to export half-a-tonne next year. Do the math.

But on top of that he sold the acorns from the oak to feed livestock, with chemicals in the acorns reducing their greenhouse gas emissions.

He said it was a common misconception that truffles were only good for three days.

"High-quality truffles that are lively and not affected by herbicide can easily take the trip from Braidwood to London and retain their flavour and aroma for a couple of weeks," Mr Marshall said.

His truffles - farmed without herbicides - are shipped across the world, to the United States, France, England and now Japan.

But it's also his packing system that's helped, he said. Mr Marshall spent several years developing packaging allowing the truffles to continue breathing throughout their trip to retain their aroma.

Some chefs want small truffles to shave at the table, others want larger ones for the back of the kitchen.

"They taste great and you can use them in very simple ways," Mr Marshall said.

"We love working with the top chefs because they're so technically adept, but they're also artists, which is why we enjoy having them come to the farm."

"We've had unbelievable experiences."