coffee-chemistry-ph-acidity

Coffee Acidity – Flavor, pH, Acid Reflux, and Low-acid Coffee: Part 1

Depending on who you ask, acidity in coffee is either a) the cause of heart burn and/or acid reflux, or b) the source delicious fruity complexity, a highly desirable characteristic of the best coffees. Armed with a digital pH probe and inspired by an episode of Sesame Street I was watching with my son, I set out to learn a little bit about acidity in coffee. Basically I wanted to answer two questions:

  1. Does the acidity we taste in coffee correlate in any way with the actual pH of the coffee?
  2. If there is a difference, can it be significant enough to support claims made by roasters of “low-acid” coffee?

Before I bore you with text, here are the pH readings I took over the weekend:

Substance  pH
Whole Milk 6.9
NYC Tap Water 6.7
Sumatran Coffee (low acidity) 4.6
Panama Coffee (medium acidity) 4.5
Kenyan Coffee (high acidity) 4.3
Apple Juice 3.8
Grapefruit Juice 3.6
Blueberry Lemonade 2.9
*If it’s been a while since you took chemistry in high school, a pH of 7 is neutral, and a lower pH means more acidity.

Coffee Acidity: Flavor vs pH

I went into this experiment assuming that there would be absolutely no pH difference between coffee that tasted very acidic or not acidic at all. Surprisingly, there was a small but direct correlation with flavor and pH. To perform the experiment, basically I brewed three coffees at the same time, 4 minute brew time, 16:1 brew ratio, then let them cool to about 100 ℉. Kenya is a region known for very high acidity (in a good way) and this coffee in particular was SL-28, the most acidic varietal. Sumatra is a region known for very low acidity, and this was a particularly flat Sumatra. We didn’t ship it in our subscription (and no, it wasn’t from Bespoken, that picture above is just to show off my fancy lab-ware). The Panama was somewhere in-between. You’ll just have to trust my tastebuds on that one. Or as it turns out, my pH probe.

Because I went into this experiment expecting to see no difference in pH, I sorta skimped on the freshness. The coffees I sampled were 3 weeks old, and the acidity was noticeably lower (in terms of taste) than when they were fresher. I was concerned that freshness would mess up the pH readings because fresher beans contain carbon dioxide, and CO2 increases acidity. However, based on these results, I’m curious to test a batch of coffee 3 days off roast to see if the difference is more noticeable. Stay tuned for a Part 2 where I will present more data on fresher coffees, and track changes as they age.

Low-acid Coffee and Acid Reflux

I have no doubt that people experience stomach issues from coffee, but I strongly doubt it has anything to do with the acidity. In addition to my list above, here’s a list of pH values for common foods from the FDA. If you think coffee is bad, you probably also can’t eat almost any fruits, tomato sauce, or napoleons and eclairs.

More importantly, the difference in pH between very acidic and very flat coffees is probably not significant enough to cause or prevent stomach issues.  So if you have been, or are considering switching to a low-acid coffee, I recommend you think twice. It’s more widely accepted that the caffeine in coffee is what causes irritation because it stimulates the release of more stomach acid. It’s an easy theory to test, try a caffeine pill, a red-bull, or 5-hour energy. Tea and soda also have caffeine, but in lower doses.

Coffee Flavor

The reason I’m so opposed to blaming heartburn issues on pH is because acidity brings with it a ton of interesting fruit flavor and complexity. Have you ever had a cup of coffee that’s naturally sweet and tastes like blueberries without any weird additives? If not, then you’re missing out. Subscribers to Angels’ Cup get to blindly sample up to 208 different coffees per year! Insane variety and blind tasting are the only way to learn how different origins taste.

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