Millions of Americans drink decaf coffee to get that perfectly bitter taste without all the jitters.

But does decaf really have no caffeine? What’s the difference between "decaffeinated" and "naturally decaffeinated”? And are the chemicals used to strip the caffeine from coffee safe?

To understand what’s in your cup of decaf, you first need to understand what’s not in it.

FDA regulations specify that for coffee to bear a decaffeinated label, 97 percent of the original caffeine must be removed from the beans. So, yes, there’s caffeine in decaf coffee. But it’s not very much, right?

Not so fast. Caffeine content varies from bean to bean.

Coffee in America generally contains one or a blend of two bean types – the hardy Robusta bean and the sweeter, delicate Arabica bean. Robusta beans generally contain twice the caffeine of Arabica beans, but their harsh taste is often considered inferior. Instant coffee brands like Folgers and Maxwell House tend to be Robusta blends, while coffee houses like Caribou and Starbucks pride themselves on their pure Arabica beans.

While 97 percent of the caffeine must be removed, the Robusta bean will have more caffeine left over than the Arabica bean after the decaffeination process is completed, which can lead to a lot of variance among brands.

The FDA does not require the amount of caffeine to be labeled on decaffeinated coffee products, but the upshot is that if you’re looking for less caffeine in your cup, you should pay attention to the type of bean that goes into it.

The average 12-ounce cup of decaf coffee – a Starbucks tall – usually contains between 3 and 18 milligrams of caffeine. (By comparison, an 8.4-ounce can of Red Bull contains 80 milligrams of caffeine) The average of amount of caffeine in regular coffee can vary significantly, usually between 140 and 300 mg.

In 2007, Consumer Reports studied cups of decaffeinated coffee from popular chains. While most cups had fewer than 5 milligrams of caffeine, one cup from Dunkin Donuts contained a whopping 32 milligrams, and another from Seattle’s Best came in at 29 milligrams – certainly not a caffeine-free choice . In their sample, decaf cups from McDonald’s consistently had the fewest milligrams of caffeine.

Maria Bella, a nutritionist who founded Top Balance Nutrition, a weight management and healthful eating consulting center, in New York City, says caffeine sensitivity will affect how jittery you feel, and it may be influenced by other factors like diet and daily schedule.

She stresses that there is no such thing as coffee with zero caffeine in it.

“Beverages should only be considered ‘caffeine-free’ if there was never any caffeine in the ingredients to begin with,” she says. “Coffee and non-herbal teas should not be labeled caffeine-free.”

So how do you get (almost) all that caffeine out of the coffee, anyway?

The caffeine is removed from green coffee beans, before they are roasted, and there are a number of different processes, all of which affect the roasting process and how long the coffee stays fresh. (Decaf coffee goes stale almost twice as fast as regular coffee.)

The first decaffeination method, developed in the early 1900s, used a repetitive rinsing process aided by the chemical benzene, which is no longer used because it is a known cancer-causing agent.

Today, like seasoned vintners, coffee processors favor different decaffeination methods for optimum taste and quality.

Many brands use the Direct Process, which involves the chemical methyl chloride.

Two other methods are the Natural Process, which removes the caffeine using the plant hormone ethyl acetate or carbon dioxide, and the Water Process, which uses no chemical agents, just pure H2O.

Processes utilizing CO2 and the Water Process, pioneered by  SWISS WATER®, are both considered Natural Processes and are the only methods that can be certified organic. And while organic coffee is gaining popularity, it is still hard to find in many supermarkets.

Methyl chloride, used in the Direct Process, is listed as a possible carcinogen by the National Cancer Institute, but FDA regulations consider up to 10 parts per million (ppm) to be safe for consumption. Trace amounts of the chemical have been found in decaf coffee brews, but most blends have a concentration at or below 1 ppm.

Lorenzo Perkins of Cuvee Coffee in Austin, Texas, who has been brewing coffee for 13 years, says that small trace is not a cause for concern. As a SCAA—Specialty Coffee Association of American-- certified level 2 barista and vice chair of the Barista Guild of America, he’s seen it all when it comes to coffee production.

“Methyl chloride has the least affect on taste because of the way the chemical bonds with the alkaloids in caffeine,” Perkins said. “It leaves the other organic material alone, resulting in a superior tasting coffee.”

Nonetheless, coffee producers are increasingly sensitive to consumer concerns about additives. Starbucks, which uses methyl chloride to decaffeinate most of its blends, now offers a “naturally processed” decaf Sumatra brew. Caribou Coffee uses a non-chemical water process in all its decaf blends. And the Coffee Bean says it tests its decaffeinated blends to ensure that there are no chemical residues from the process it uses.

One final note about decaf: Studies have linked excessive regular coffee drinking to hypertension, decreased bone density and high levels of gastric acidity. And while switching to decaf might help with insomnia, those looking to avoid other unwanted health problems associated with coffee should not assume that eliminating their caffeine intake is the answer.

“Many health conditions that are affected by coffee are also aggravated by drinking decaf, due to the phytochemicals that remain after the decaffeination process,” Bella said.

These conditions include increased gastric acidity (heartburn or GERD), interfering with mineral absorption (particularly iron) and increased incidence of rheumatoid arthritis.

Bella says that up to 400 milligrams of caffeine is considered fine for most adults in good health.