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Your stomach and coffee

2015 January 27
by Ryan

This morning I noticed a tweet from @SpringsCuisine about darker roasts being easier on the stomach than lighter roast coffees. When I commented back that I disagree, I was given a link to a study done by molecular scientists confirming this fact.

Here’s my issue with this study: at a molecular level, they are most likely right. But there’s way more to the chemistry of coffee and the art of the roast than that article explained. (please note I just went off of the abstract of the article: the more in-depth article was behind a paywall)

(Warning: this is gonna get technical at first, but bear with me……..)

First and foremost, let’s talk about acids versus acidity. These terms are not the same when talking about coffee. Many types of acids are present in coffees, some good and some bad. Acidity is all about the “brightness” the coffee imparts in flavor: does it “pop” on your tongue or does it lay there like a wet blanket? These terms are not and should never be interchangeable. Acidity=good. Some acids=bad. Okay? Okay.

Let’s first talk about what coffee is: an organic product that is grown and harvested. Just like corn, potatoes, oranges, etc. As with its other grown-and-harvested counterparts, the chemical composition is made up of many ingredients: from soluble carbohydrates to oil to proteins. For coffees, in the roasting process, many of these ingredients stay the same–in fact, their respective percentage points increase due to the loss of water weight.

The coffee bean starts as the seed of a coffee cherry.

The coffee bean starts as the seed of a coffee cherry.

In the roasting world, the Chlorogenic Acids (CGAs) are the ones to really control: they show in the cup as the acidity/bitterness component. The other minor organic acids present in the coffee bean will be prominently displayed in lighter roasts and diminish as the roast continues into darker phases. This part is in the article, and there is no argument from me there. (Sources: The Coffee Roaster’s Companion by Scott Rao Available here and The World Atlas of Coffee by James Hoffmann. Available here)

But now we need to explore what the article completely and utterly ignores: the freshness of the coffee bean.

As mentioned above, coffee is an organic product. This means it has a shelf life: it will stale over time. When coffee is fresh from the roast, it should have a smooth, dry look to the bean. Unless the coffee is quite overroasted (or decaf, but that’s another story…), no oils should be present on the bean.

Our Colombia coffee one day off the roast. Note the dry appearance of the coffee: no oils in sight.

Our Colombia coffee one day off the roast. Note the dry appearance of the coffee: no oils in sight.

The coffee at this stage is full of CO2 gases which were created with the roasting process: the loss of water, the Malliard Reaction, and the overall chemical composition changes that happen at over 400 degrees F. Immediately after the roast, these gases start pushing through the bean (which due to roast is quite porous at a magnified level). As the coffee ages, those gases push through, taking most of the aromatics with it. This is why a bag of freshly roasted coffee smells great at first but fades the longer it sits around. The gases also help with the flavor of the coffee. Think about a glass of seltzer water. When first poured, the bubbles (CO2) are everywhere and lead to an effervescent flavor. Leave that glass alone for a few hours and the taste is completely different. The water has “staled.”

After a period of about 14 days, the vast majority of the CO2 gases have escaped the bean, leaving behind the oils and acids. Since your coffee is an organic product, staling also happens right away. These oils will turn rancid over time. Not right at 14 days, but pretty quickly after that.

What happens when you drink a glass of milk from a two-month expired gallon? You end up visiting the loo, right? Your body reacts to the rancid milk. Coffee does that, too, albeit not at that extreme level. The rancid oils cause upset stomachs, heartburn, and overall yuckiness to your body. This has virtually nothing to do with the acids present in the coffee–just the oils. Ever look at your cup and see an oil slick across the top? That’s the coffee oils.

FACT: in our seven years of existence, I have only had one person tell me our coffees affected them–and they admitted to a hypersensitivity to caffeine. The majority of our roasts are lighter on the roasting scale (our darkest roast is equivalent to Starbucks’ Blonde roasts!). This empirical data directly refutes the study in question. The difference: our coffees are fresh.

The dirty little secret of the mass-production coffee industry is that since the reactions are not life-threatening (usually), stale coffees can be the normal. If your stomach hurts after drinking a cup, the mass coffee companies can say that it is the acids that cause the problems. And then sell a “low acid” overroasted (or chemically treated: it was directly mentioned in that linked article!!!) coffee at a marked up price. Because Joe Consumer will pay for it.

Your better bet versus trusting a bunch of chemists is to trust a bunch of coffee roasting professionals: talk to your local neighborhood roaster to get a coffee that won’t tear you up. Make sure the roast date is on the bag, and find that coffee that hits your desired flavor profile. And kiss that sour stomach goodbye.

I’m off my soapbox now. And I’m going to go have a cup of a nice, light roasted coffee that won’t mess up my stomach.

Happy drinking!


Springs Cuisine came back at me with another article, this one from Wired Magazine, saying the same thing about darker roasted coffees. From the article:

To explore the science behind these gentler brews, Somoza and her colleagues used water and three other solvents to extract compounds from regular commercial coffee blends.

I would like to point out the last four words of that quote: regular commercial coffee blends. So the mass-produced coffees. Made by companies that don’t care about your stomach, much less the quality and freshness of the coffee–just that you’re still spending your money on their product. I still believe the study is flawed simply due to the fact that the scientists did not account for every variable. Namely, that the coffees they were testing were way beyond stale. If the scientists were to take some freshly roasted coffees direct from any roaster and test for stomach issues (NOT the acid levels: I agreed earlier that the acids are present!!!) I bet they’d change their stance.

I welcome any comments to the contrary, and I’m willing to change my stance if you can disprove my last seven years of real-world data.


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