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The scenes along the Amazon were unforgettable: grown men shimmying up huge palm trees in search of what has become the most-sought-after new food in the world.
"This is the skinny palms, you know; the black fruit there is the acai," said Monteiro.
The trees do not grow big and thick like the palm trees most people know.
Acai grows in the wild in clusters at the top of the skinny palm trees. It's bigger than a blueberry, smaller than a grape. People call it a berry, but it has just one seed ... so it's actually a fruit.
It's like a rock to bite.
"Actually, you need to take off the skin, and the skin makes the puree or the pulp we mix with water," Monteiro said. "It has kind of a coconut inside."
In the Amazon, a common site is a man scooping acai from a bucket and putting it into a juicing machine.
You don't eat acai, you drink it. The bland pulpy purple juice is not new to the people who live in the villages and cities of the Amazon. Almost everyone in this part of the Amazon seems to drink it. They say it's full of vitamins and gives them energy.
The signature red flag of an acai stand can be seen on almost every corner.
Brazilian athletes first helped turn acai into a sensation across the country a decade ago. ABC News stopped by a very humble jiu-jitsu gym in the Amazon city of Belem to see just how common acai is here.
Asked whether they drink acai, many of the athletes raised their hands.
Martial artist Rafael Andrade told "Nightline" he'd been drinking acai since he was a little boy. He said he drinks it before and after practice and that if he didn't drink it he would have less energy.
"I would fall asleep," Andrade said. "I would be much more tired."
But in the U.S., acai is being pitched by some as much than an energy drink. The Internet is filled with Web sites promoting acai pills for miracle weight loss. Others say it can offer added push to your sexual potency, or even a cure for cancer. It's hard to know what to believe.
To separate fact from fiction, ABC News spoke to some of the top food scientists in the U.S., at Texas A&M University.
Husband-and-wife team Steve Talcott, a biochemist, and Susanne Talcott, a food chemist, first began looking at acai in 2004. Although the scientific studies are not complete, what is clear is that acai does have extraordinarily high levels of antioxidants, which can help combat the effects of aging and heart disease.
"It's not a miracle berry, unfortunately," said Steve Talcott. "It is superior in antioxidants; it does have a very high antioxidant capacity. There is some really unique chemistry to the fruit. But it's not a drug. It's not a miracle, cure-all fruit. I mean this is a dietary component. The recommendation is to incorporate these fruits into our diet, but don't use them as drugs.
His wife concurred.
"Currently, there is no direct evidence, scientific evidence, that acai has any weight loss properties," said Susanne Talcott.
"The problem we have again," said Steve Talcott, "is that the marketing hype with acai seems to have surpassed the science."
Acai got its marketing push in the United States when Oprah, Dr. Mehmet Oz and other TV gurus enthusiastically discussed it.
They didn't claim miracles, but Oprah and Dr. Oz did label it a "superfood." That's not a scientific term, but it's a term that scam artists on the Internet seized upon, taking images of the TV duo without permission to promote weight loss supplements ... and steal people's credit card numbers.
FWM Labs, based in Hollywood, Fla., maintained a Web site promoting acai capsules. The site offered a "free" sample for a nominal fee for shipping and handling.
What followed, authorities say, were unauthorized $80 monthly credit card charges that couldn't be stopped.
WPLG, ABC's Miami affiliate, tried to talk with the company in person -- and was referred to the company's attorneys.
Alleged victims said they had to cancel their credit cards to get charges to stop. FWM finally agreed to pay $200,000 in penalties, refund millions to customers and stop its allegedly misleading marketing.
Oprah and Dr. Oz said it's easy to spot a scam because they never endorse products.
"If my name or picture is next to a product being sold, you can guarantee it's a scam," said Oz, "because I don't endorse any products and I would never let anyone use my name or my face, image, to sell a product."
In the U.S., the scams have given acai a bad name and led to confusion. But in the Amazon, the fruit is seen as nothing less than "purple gold." The exploding demand for this little fruit has brought jobs and prosperity to a remote region that has little of either.
Selma Pinheiro's entire family lives on the river on the profits from acai, in a home built by acai.
She said they can sell 140 or 150 baskets a day during the peak season, at anywhere from $7 to $17 per basket.
Locals Maria and Luis Bosch said acai has changed life for people of the Amazon. Profits from selling the fruit brought them electricity and sent their children to school.
Acai also is helping protect the rain forest. Until demand for the fruit exploded, the only value in the acai palm was the core of the tree itself. Heart of palm is a local delicacy and a popular export, but requires cutting the trees down. Now there's more money to be made preserving the tree and picking its fruit.
To get a sense of what acai means for the Amazon, get up very early and visit the acai market in Belem, the main city in the region. By some estimates, 40,000 people in the region work with acai.
The market begins well before sunrise and the scale of it is impressive.
Bony Monteiro, the acai producer, said the market moves fast -- and with good reason.
"Look, if you take days to process, the fruit is not OK anymore," Monteiro said. "You need to process the fruit in 24 hours."
On the edge of the rainforest, Monteiro has built his processing plant, one of several sleek new acai factories in the area. His plant, Bony Acai, recently was inspected and approved by the U.S. Food and Drug Administration.
Monteiro said he had to work with engineers to develop the machinery for processing acai on a mass scale to meet world demand. "We feel here like industrial revolution here," said Monteiro. "We take the manual process, the knowledge from that people, join that people with the engineer and its happened."
Monteiro said production was growing rapidly. "I think we double every year," he said.
Bony Acai produces half-a-million dollars' worth of acai concentrate a week. Much of it now headed to the U.S. market.
On the outskirts of Belem, "Nightline" visited one of the smaller new processing plants, called Top Acai. The proprietor, Herbert Levy, joined the acai explosion when he saw his kids drinking it in Rio. He believes it's better than gold for the people of the region.
"It's much better because the gold it's only a few people who make money with gold," said Levy. "You don't have poor people who make money with gold. It's very tough. Here, you have the owner of the acai. It's not us. The owner of the acai is the people who are in the jungle of the Amazon."
But is the "purple gold" really fool's gold? According to scientists, the juice has the same healthy properties as other dark fruits, like blueberries, blackberries and red grapes. All are good for you, but -- like acai -- only as part of healthy diet with regular exercise.
"The bottom line with acai is that it is a fruit, it's not a drug," said Steve Talcott, the Texas A&M professor. "You shouldn't consume it as a drug. You shouldn't expect a drug-like effect."
Talcott believes Americans are going to see a lot more acai in our lives.
"You're going to see new forms of acai," he said. "You're going to see it in beverages. You're going to see in cosmetics. You're going to see it in more dietary supplements, you're going to see it in your shampoo. We are going to be drinking it and pouring it on your body.
"If you think it's crazy now from a marketing perspective, I think we've just seen the tip of the iceberg," he added.
Back in the Amazon, producers worry that the confusion in the U.S. market is going to give acai a bad name before people can understand how good it can be.
Herbert Levy invited us to taste some acai fresh off his production line. The fruit is so bland that it is usually mixed with juice from a sweeter fruit, but he prefers it with just a little sugar added.
Soon enough, we will all get a chance to see -- and taste -- for ourselves.