How Coffee Is Decaffeinated

Decaf has a reputation problem that is mostly out of date. The methods used to remove caffeine have improved substantially, and good decaf from a quality roaster is a genuinely enjoyable coffee rather than a compromise.

Understanding how it is made explains both why older decaf earned its reputation and why the current generation does not deserve it.

Why Decaffeination Is Difficult

Caffeine is one of roughly a thousand soluble compounds in green coffee. The challenge is removing that one compound while leaving the several hundred that carry flavor and aroma intact.

Every method works on green, unroasted beans, and every method involves water, because the beans have to be swollen and porous before anything can be drawn out of them. That step alone is a stress on the bean, and doing it badly is where flat, papery decaf comes from.

Decaffeinated beans also roast differently. They are more porous, darker before roasting begins, and they transfer heat faster, so the visual cues roasters use do not apply the same way. Some historically poor decaf was as much a roasting problem as a decaffeination problem.

Solvent Based Methods

Direct and indirect solvent methods use either methylene chloride or ethyl acetate to bond with caffeine and carry it out of the bean.

In the direct method, steamed beans are rinsed repeatedly with the solvent, which selectively binds caffeine. In the indirect method, beans are soaked in hot water that pulls out caffeine along with flavor compounds, the water is treated with solvent to strip the caffeine, and the beans are returned to that flavor-rich water to reabsorb what they lost.

Methylene chloride is the one people react to on a label. It is worth being accurate here: it evaporates at 104 degrees Fahrenheit, and coffee is roasted well above 400 degrees and brewed near 200. Residual levels in finished coffee are far below regulatory limits and are typically undetectable. The concerns that circulate about it are largely about industrial exposure rather than about drinking the coffee.

That said, many specialty roasters avoid it for market reasons, and some of the best decaf available uses other methods.

Ethyl Acetate and Sugarcane Process

Ethyl acetate is a compound that occurs naturally in fruit, including coffee cherries. When derived from fermented sugarcane, the process is often marketed as sugarcane decaf or natural decaf, and it is especially common in Colombian coffee where the sugarcane is grown locally.

Beans are steamed to open their pores, then repeatedly rinsed with an ethyl acetate solution that binds caffeine. They are then steamed again to drive off any remaining solvent and dried.

Sugarcane process decaf tends to retain good body and sweetness, and often carries a subtle fruity note from the process itself. It has become one of the more popular methods in specialty coffee because it works well and the story is easy to tell.

Swiss Water Process

Swiss Water uses no solvents at all. It works on solubility and concentration gradients.

A batch of green coffee is soaked in hot water, which extracts both caffeine and flavor compounds. That water is passed through activated carbon filters sized to trap caffeine molecules while letting flavor compounds through. What remains is a liquid saturated with coffee flavor but free of caffeine, called green coffee extract.

Fresh beans are then soaked in that extract. Because the liquid is already saturated with flavor compounds, those compounds have no gradient to move along and stay in the bean. Caffeine, absent from the liquid, migrates out. The extract is refiltered and reused.

Swiss Water is certified to remove 99.9 percent of caffeine and it is chemical free, which makes it the default choice for organic certified decaf. It is also more expensive, which shows up in the price of the finished coffee.

CO2 Process

The carbon dioxide method uses CO2 held at high pressure in a supercritical state, where it behaves as something between a liquid and a gas. In that state it is highly selective for caffeine and largely ignores the larger flavor molecules.

Moistened beans are placed in a vessel and supercritical CO2 is circulated through them. The caffeine-laden CO2 moves to a separate chamber where the pressure is released, the caffeine drops out, and the CO2 is recycled.

Flavor retention is very good. The drawback is capital cost, so it is used mostly at large scale, which means you see it more often in commercial and supermarket decaf than in small lot specialty coffee. The extracted caffeine is sold on to the soft drink and pharmaceutical industries, which is true of most methods.

How Much Caffeine Is Left

Decaf is not caffeine free. In the United States, coffee labeled decaffeinated must have at least 97 percent of its caffeine removed. Swiss Water and CO2 typically reach 99.9 percent.

In practice a cup of decaf contains a small residual amount, generally in the range of a few milligrams, compared with roughly 95 milligrams in a typical cup of regular coffee. For most people that is negligible. For someone with genuine caffeine sensitivity, several cups of decaf in a day still adds up to something.

Species matters as well. Robusta contains roughly twice the caffeine of arabica before any processing, which our guide to arabica versus robusta covers in more detail.

Why Decaf Behaves Differently When You Brew It

The decaffeination process makes beans more porous and more brittle. That has real consequences at the grinder and in the brewer.

Decaf tends to grind finer at the same setting because the beans fracture more easily. If you switch a regular coffee for a decaf without adjusting, your shot will likely run slower and taste more bitter. Start one or two steps coarser than you would for the same roast level in regular coffee.

Decaf also extracts faster, so it is easier to overextract. And because the beans are already darker going into the roaster, decaf is frequently roasted a shade lighter than it appears, which is one more reason to dial it in on its own terms rather than assuming your existing settings transfer.

Our grind size guide covers the adjustment ranges by method.

Reading a Decaf Label

Good decaf labeling names the method. Look for Swiss Water Process, sugarcane or EA process, CO2 process, or mountain water process, which is a water based method using water from Pico de Orizaba in Mexico.

A bag that says only decaffeinated without naming a method is usually a solvent process, and often a commodity coffee. That is not automatically bad, but it tells you less.

Everything else on the bag still applies. Roast date, origin, and processing method all matter as much for decaf as for regular coffee, and a stale decaf from a good process is worse than a fresh one from a plain process. Our guide to reading a specialty coffee bag covers the rest of the label.