Decaffeinated coffee, though trendier than ever, is nothing new.

A German entrepreneur, convinced that his coffee-merchant father had died from consuming too much caffeine, patented the first decaffeination process in 1908. The product, Sanka, took its name from the French "sans caffeine." Later General Foods Corp. acquired the Sanka trademark.

The original Sanka decaffeinating process -- in which a chemical solvent extracted most of the caffeine from steamed coffee beans -- is still in use, but the solvents have changed.

In 1975, after National Cancer Institute-sponsored studies found that trichloroethylene (TCE) caused cancer in mice, companies switched to another solvent, methylene chloride. But methylene chloride now is under investigation because preliminary studies suggested that high doses may cause liver cancer in mice.

The Food and Drug Administration last December proposed a ban on use of methylene chloride in cosmetics, but permits use of the solvent to decaffeinate coffee as long as residues remaining in the coffee were 10 parts per million or less. Typical residues are less than 0.1 parts per million -- well below the limit -- an agency spokesman said. In 1981, FDA approved use of another solvent, ethyl acetate, which occurs naturally in many foods.

Michael Jacobson, executive director of the Center for Science in the Public Interest, called the FDA's failure to ban use of methylene chloride "shameful," but conceded that the reported residues of the solvent are "extremely small" and advised people who are susceptible to caffeine's effects to keep the risk in perspective.

For those people, Jacobson said, caffeine poses "a far greater risk than the residues of methylene chloride in decaf coffee."

Some decaffeination methods don't use chemical solvents. The Swiss use a water-based technique that is not used in the United States. Another process uses a mixture of steam and coffee oils.

Decaffeination removes at least 97 percent of the caffeine from coffee. But decaffeinated coffee is not without health effects. Like regular coffee, it stimulates secretion of stomach acid. And it also can cause heartburn.

Popular alternatives to caffeinated or decaffeinated coffee, include:

*Regular tea, which contains about one third to one half as much caffeine as brewed regular coffee. Besides caffeine, however, it contains small amounts of theophylline, another stimulant, and tannic acid, which can irritate the stomach.

*Herbal teas, available in a variety of flavors. They are usually caffeine-free, but are not without possible health effects: Herbal teas may contain ingredients that could have a medicinal effect in some people, but are often not listed on the label.

*Grain-based drinks, such as Postum and Cafix. These are caffeine-free and low in calories. Their taste is distinct from that of coffee or tea, and they can have a laxative effect in some people.