Coffee Acidity Mini Series - Part 1

March 26, 2020

Acidity in coffee

We’ve recently had a few different inquiries come through about the acidity of our coffee and how it might compare to other coffees advertised as “low acid”. So, we’re putting together a mini-series of blog posts in which we’ll dive in to the concept of acidity a bit. We’ll take some measurements of our own in order to get an idea of how our coffees (both CBD infused and non-CBD infused) compare to other coffees and common beverages. Below is a break down of the posts in this mini-series.

 


 

Part 1:   Discussion of Measured vs. Perceived Acidity in Coffee

Part 2:   Actual Measured and Perceived Acidity in Coffee, Water and Other Beverages

Part 3:   Discussion of Findings and Lessons to Take Home

 


 

Part 1 – Discussion of Measured vs. Perceived Acidity in Coffee

*Before we proceed, we would like to mention that the findings presented here are purely a product of our own experimentation and that we cannot guarantee the acidity of anything that we did not directly measure in the investigations that we carried out. If you have specific health or dietary reasons to seek out beverages with particular acidity levels please consult with your physician before making any decisions about what is safe or ideal for you to consume.

To start, we'd like to draw a distinction between measured acidity and perceived acidity in a beverage. The two are linked, but there are some important differences that will inform the rest of our investigation.

Measured Acidity:

A solution’s acidity/basicity is defined by a measure known as pH. The pH scale is a measure of Hydrogen ions in a solution which ranges from 1 to 14 (these numbers are actually the negative logarithm of the hydrogen ions present, but that is a separate topic). For our purposes, it will suffice to know that solutions with a pH of 7 are considered neutral while a pH below 7 is considered acidic and a pH above 7 is considered basic.

There are a few ways to measure the pH of a solution. One that might be familiar from grade school chemistry courses is the use of litmus paper or indicator dies. The color shown on a piece of litmus paper that is submerged in a solution or produced by particular indicator dies that are added to a solution is matched against a chart calibrated in pH. These tests are quick and easy, but do not provide the most accurate or precise results. For that reason, we have decided to use a digital pH meter. This instrument has two electrodes that are simultaneously submerged in a particular solution. The concentration of Hydrogen ions in that solution creates a voltage difference between the two electrodes. By measuring this voltage difference, the meter is able to discern the quantity of hydrogen ions present and, therefore, the pH of the solution being tested.

Perceived Acidity:

In the section above, for the sake of establishing a quantifiable variable, we defined an acidic solution as one that has a pH below 7. Having a quantifiable variable is quite useful when attempting to make an objective comparison of two or more items. While that’s all fine and dandy, the reality is that when tasting things like coffee or juice or wine we do not definitively measure the pH of the beverage with our tongue. Thus we find ourselves in the subjective realm of qualitative analyses. We can talk about how acidic a beverage seems to us, but this does not necessarily translate into a precise measure of the type or quantity of acids actually present in a beverage. 

Acids by themselves often impart a sour flavor and sticky or drying mouth feel. Think of orange juice (citric acid), sour milk (lactic acid) or pears/apples (malic acid). Some acids may be more easily perceptible than others and some may only present themselves when paired with other acids or non-acid compounds. This is all to say that just because something imparts flavors that are common to particular acids, the pH or measured acidity of that something might not directly correlate to the sensation of acidity we experience.

Discussion of Acids in Coffee

As they grow inside the cherry of a coffee plant, coffee beans naturally develop numerous chemical compounds ranging from sugars to acids to salts. The specific compounds that develop in any particular bean are a product of innumerable variables including the genetics of the parent plant, soil conditions, altitude, humidity, presence of shade, processing methods used during and after harvesting and many more. In addition to the wide variation of compounds that develop in green coffee beans while they are growing, the roasting process can alter, release and/or degrade all of these compounds in numerous ways. After roasting, particular brewing parameters like grind size, water temperature, brew time, etc… will have a significant impact on what compounds actually make it from the bean into the cup.

All this is to say that a myriad of innumerable variables will affect the compounds that make it from a green coffee bean into the cup of joe that is in your hand. It is the dramatic variation in what compounds are present in a cup of coffee that brings about the importance of distinguishing between measured acidity and perceived acidity in coffee. This wide variation also hints at the fact that one particular green coffee may translate into cups with considerably different measured and perceived acidity levels based on how that green coffee was roasted and then brewed.

As established above, in an objective sense, acids are compounds that will alter the pH of a solution in such a way that the pH measures below 7. In a subjective sense, acids are compounds that impart a sour, sticky or drying sensation. Think of biting into a lemon. The sourness you experience is a product of the citric acids present in that lemon. The pH of a solution can be measured; the way something tastes will vary from person to person and is subject to things like the unique combination of flavor receptors one has as well as one’s tasting vocabulary and mental library of different tastes.

When tasting coffee, we are not able to perfectly perceive all of the acids present in the cup nor exactly identify the quantity of acids present (though some highly experienced tasters might be able to come somewhat close). One reason for this is because of the interplay between acids and other compounds present in coffee. Certain compounds may act to mask or amplify the acids that are present and create the unique taste experience that is that particular cup. It is worth noting here that when coffee tasters are learning to taste for different acids, they do not taste the acids by themselves, but rather, put the acids into already brewed coffee. They do this for the sake of taking into account the interplay between those acids and the other compounds present in brewed coffee. This is all to say that different perceptions of acidity in coffee do not necessarily directly map on to the actual, measurable pH of a given coffee. For most health conscious individuals, the actual pH is what’s important; for most coffee enthusiasts, the perceived acidity is what’s important.

In the experiments carried out in the following blog post we will report both perceived and measured acidity in coffees roasted and brewed in a handful of different ways from a handful of different origins. We will also compare these coffees to the perceived and measured acidity of a few common beverages and different types of water.






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