Few products in history can match the mythology and ubiquity of Coca-Cola. Started in 1886 by John S. Pemberton, a pharmacist and former Confederate soldier, the company has changed hands several times in its existence. Yet the storied formula of its marquee offering has remained an impressively guarded company secret known only to a few top executives. Owing to some dubious health claims and an innovative marketing strategy—it’s believed to have been the first product to employ coupons—Americans fell fast and hard for Coke.

Of course, no love affair is without its rough patches, and, by the 1930s, Coke’s inscrutability found itself at odds with a niche, but rapidly growing, consumer base: Orthodox Jewish immigrants whose dietary restrictions prevented them from consuming anything that didn’t meet rigid rabbinical guidelines. So, how was Coke ultimately kashered while keeping its prized formula a secret? Through compromise and chemistry.

OUT WITH THE OLD

In 1935, new world consumerism and old world mores found an unlikely intersection in Atlanta, Coca-Cola’s headquarters. Approaching its 50th birthday, Coke was a national icon, available at nearly every soda fountain in the country. Millions of gallons were being consumed every year, many of those by immigrants who, by that point, had settled all over the country. Enter Tobias Geffen, a Lithuanian Jew who’d moved to Atlanta 25 years prior to lead Congregation Shearith Israel. Seeing that Rabbi Geffen and Coke were essentially neighbors, rabbinic leaders from around the country began to write him, asking if it was permissible for Orthodox Jews to drink Coke based on what he knew about the ingredients. Unsure how to reply and unaware of Coke’s staunch protection of their formula, he contacted the company and asked for a list of the ingredients.

Amazingly, Coke agreed to share the list on the condition that Rabbi Geffen swear the formula to secrecy. They didn’t, however, include the amounts of each component, which is as important as the ingredients themselves. Upon examination, Rabbi Geffen noticed that it included glycerin, used as a sweetener, derived from non-kosher beef tallow. Though it was present in small enough amounts to technically meet kosher standards, Geffen decided that, since it was added intentionally and not as a necessary byproduct, he couldn’t sign off on certification. After hearing his ruling, Coke chemists set out to find a tallow substitute that would meet kosher standards without changing the taste. They honed in on a glycerin made from cottonseed and coconut oil that left both parties satisfied, and Geffen gave it his approval.

Still, one problem remained. At Passover, an even stricter set of dietary constraints are followed, and the miniscule amounts of alcohol in Coke from grain kernels were chametz—a Passover no-no. Coke’s scientists hit the lab once again and found that sweeteners from beet and cane sugars could be substituted for grain sweeteners without affecting the taste. Ever since, in the weeks leading up to Passover, Coca-Cola releases a modified formula using cane sugar instead of high fructose corn syrup (just like the much sought-after Mexican Coke), which is bottled with a yellow cap to signify it’s kosher for Pesach.

COKE AND DAGGER

Discounting a single disastrous reformulation in the mid-80s, Coke’s taste has remained remarkably consistent over the past century, which, more than marketing or ubiquity, is likely the greatest contributor to its longevity. Even so, the drink is still subject to periodic rabbinical review to uphold its kosher status. Coca-Cola executives are not quite as forthcoming with its secrets as they were in Rabbi Geffen’s time, though. Now, the company simply provides an overstuffed list of ingredients for approval, all of which are known to be kosher, but only a handful of which are actually used in the formula.