The recipe is a secret. It is kept in a vault that is on display, but the recipe itself as with its other products are considered trade secrets.
A trade secret is any information that allows you to make money
because it is not generally known. A trade secret could be a formula,
computer program, process, method, device, technique, pricing
information, customer lists or other non-public information. If the
economic value of a piece of information relies on it being kept
private, it could be a trade secret.
One of the most famous examples of a trade secret is the formula for
Coca-Cola. The formula, also referred to by the code name "Merchandise
7X," is known to only a few people and kept in the vault of a bank in
Coca-Cola and all of its varieties have their basic ingredients listed on their home page. As noted below some key ingredients are listed in a way that makes the specific ingredient difficult to tell. Since they provide the final product to consumers without licence it is hard to say that it (the final product) is a secret. The recipe to make it, as noted above, is a secret. Wikipedia has some links to recipes proported to have been used.
In 2006 a disgruntled employee tried to sell the Coke recipe to rival Pepsi.
when PepsiCo Inc. got a letter offering Coke trade secrets, it went
straight to its corporate rival.
Six weeks later, three people were scheduled to appear in federal
court Thursday to face charges of stealing confidential information,
including a sample of a new drink, from The Coca-Cola Co., and trying
to sell it to PepsiCo.
on June 27, an undercover FBI agent offered to buy other trade secret
items for $1.5 million from "Dirk." The same day a bank account was
opened under the names of Duhaney and Dimson, and the address used on
the account was that of Duhaney's residence, prosecutors said.
Video surveillance showed Williams at her desk at Coke headquarters
going through multiple files looking for documents and stuffing them
into bags. She also was observed holding a liquid container with a
white label, which resembled the description of a new Coca-Cola
product sample, before placing it into her personal bag, prosecutors
say, adding that Coca-Cola later verified the sample was genuine and
is a product the company is developing.
So while the composition is not a secret, the recipe to make it the drink that it is, is.