As the high-end rum movement gains steam, enthusiasts are starting to take a critical look at premium rums. Once revered brands have recently sustained hits to their credibility, as marketing puffery is repeatedly exposed. A primary example: The sweetening of high-priced rums to make them “smooth” was once universally denied by brands, but thanks to both government testing and a band of hydrometer-wielding rum geeks, the widespread adulteration has since been revealed.

However, sweetening is just one front in the battle for rum’s future. Solera aging is also a hot-button topic, and well-known players like Ron Zacapa, Santa Teresa, Botran, Dictador and La Hechicera all proudly proclaim solera aging. But what exactly does that mean? And what of their age claims? To wit: Does the average consumer understand the difference between the $100 Appleton 21 Year, a rum aged a minimum of 21 years, and the $40 Ron Zacapa Solera 23, a blend of rums aged between six and 23 years? From looking at the labels, the difference is clearly not obvious. And while some countries, like the U.S., now have strict requirements covering label age claims, enforcement is spotty and loopholes are rife.

The term “solera” originates from the region of Andalusia, Spain, known as the Sherry Triangle. Here, fortified wine goes through choreographed iterations of casking, blending and re-casking as a matter of traditional sherry production. A simplified model of solera aging is this: Picture five casks, each completely filled with wine and stacked vertically. To bottle a small portion, you’d extract (hypothetically) one-quarter of the wine from the bottom cask, before refilling that cask with the same amount of wine from the cask immediately above. This refilling process repeats all the way to the topmost cask, which is refilled with new, unaged wine.

Do this enough, and you’ll create a system where the topmost cask holds the youngest wine, while the bottommost barrel holds the oldest. The bottom cask is known as the solera, meaning “soil,” as it rests closest to the ground. All of the casks above it are known as criaderas (“cradles”). By convention, the set of all barrels (all of the criaderas and the solera casks) is known as a solera system.

Solera aging has two important differences compared to static aging. What you extract from the solera is remarkably consistent each time, and any differences in the character of the wine or individual casks average out over the system. As such, assigning an age to solera-aged sherry is tricky. At best, the sherry maker can calculate both an average and minimum age at extraction. However, these are estimates, and producers rarely make age claims, except for vintage production.

When it comes to solera aging of rums, nearly all producers are found in former Spanish colonies, such as Guatemala, Venezuela and Colombia—hence the influence of Spanish aging techniques. However, enthusiasts are challenging whether these rums are truly solera-aged and, more importantly, whether their implied age statements are accurate.

“I’ve visited nearly every distillery exporting rum to the U.S. today and have yet to see one ‘true’ solera system,” says Ed Hamilton, a rum expert, importer and author of two books on rum. “I see dynamic blending arrangements producing some of my favorite rums, but I’ve not seen one solera system.” Despite being tethered to a time-honored tradition in Spain, historically, solera aging was “not a rum thing,” says Hamilton. “Santa Teresa was the first to use solera on a label… in the ’90s, and Zacapa soon followed.”

So if rum producers who use the word “solera” on their labels and in their branding aren’t adhering to the traditional solera method, how exactly are they aging and blending?

“We age our rum using a unique process, which is an adaptation of a Spanish sherry maturing process,” says Lorena Vásquez, master blender for Guatemala’s Ron Zacapa. “This enables rums of varying ages and personalities to be carefully blended and matured in a series of casks previously used to store American whiskeys, delicate sherries and Pedro Ximénez wines.” And then the critical point: “Differing from the sherry solera system, the barrels are changed every time a new mixture is realized, which gives an extraordinary depth of flavor.”

While Zacapa’s aging regimen certainly creates rum that is much enjoyed by consumers, it differs substantially from traditional sherry solera techniques. There is no intermingling of rums from prior batches in each cask, and no criaderas holding spirit with different average ages. In addition, by swapping in new barrels, the extraction of each barrel’s previous contents is maximized. By contrast, sherry soleras use the same barrels for decades, and their neutrality is key.

Miguel Riascos, managing director of Columbia’s La Hechicera, which produces Solera 21 rum, downplays the usefulness of a true solera system in rum, arguing that “the solera method ignores the subtleties and nuances of individual barrels.” He says that La Hechicera uses the same principles of solera aging, but chooses to “to celebrate each barrel’s individual character when assembling our final blends.” Picking casks with specific flavors to create a final blend is a long tradition in spirits-making, but it’s the exact opposite of true solera aging.

Another point of contention is age statements—or more accurately, what could be construed as an age statement. Scroll through Facebook groups like Ministry of Rum, The Global Rum Club or La Confrérie du Rhum, and the term “solera” pops up frequently, and rarely in a positive light. Both the validity of the solera term and implied age statements are the most common targets of criticism. Posts about solera-aged rums are filled with comments like, “Aged for 15 solera years. Is that like dog years where 1=7?”; “Even the word “solera” is a lie”; and “I typically run away when I see solera and Panama.”

While Zacapa’s label doesn’t explicitly say “23 years,” the average consumer would be forgiven for thinking every drop is aged at least that long. This isn’t a minor point. A quick online search for “Zacapa” reveals that many retailer listings say “23 year.” If retail sellers can’t accurately deal with this subtlety, what hope do consumers have? And is this fair to brands who use actual age statements on their labels?

Foursquare Rum Distillery’s Richard Seale, a vocal critic of solera aging, minces no words: “The law requires that an age statement name the youngest rum in the bottle. Any age claim beyond that is illegal,” he says. “Putting an isolated number on the label, which is then universally mistaken for a legitimate age claim, is a despicable, deceptive practice and should be condemned.”

Using numbers easily construed as an age statement isn’t limited to Zacapa. Matusalem, from the Dominican Republic, has “7”, “15” and “23” expressions, the numbers representing an average age, not a minimum. La Hechicera, meanwhile, recently added the words “Solera 21″ to their revamped label. Riascos defends the decision as being a logical means of expressing the rum’s provenance.

“Our family company had been in the business of aging and blending rum for 21 years,” he says. “Since La Hechicera is a selection of rums aged at least 12 years… it necessarily implies rums aged 12 to 21 go into the final blend. This is clearly mentioned in our product’s back label.”

While the average spirits buyer may not know or care about different aging techniques, the semantics matter to those working to elevate rum’s reputation and bring greater transparency to the category. There are many objectively great rums available at a fair price, including some from solera-touting producers, but there is a reason that “drink what you like, but know what you’re drinking” has become a rum-geek battle cry.