Coffee Acidity Mini Series - Part 3

April 17, 2020

Results of Experimentation

Part 3 - Discussion of Findings and Lessons to Take Home

Now, the part we’ve all been waiting for: Part 3 of our coffee acidity mini-series. Here we’ll reveal the results of the experiments that we carried out and talk about what those results might mean! We have some interesting discoveries for those of you that are curious about how to find coffees with relatively low acidity. If you’re new to this series, check out parts 1 and 2 to get an idea of what we’ve been up to. In part 1, we discussed the differences between perceived and measured acidity in coffee. In part 2 we laid out the specifics of the experiments that we did. Here in part 3 we’ll present the results of our experiments and discuss some potential implications of those results. Hold on tight because there’s a lot to dig in to here!

*As mentioned in parts 1 and 2, the findings presented here are purely a product of our own experimentation and we cannot guarantee the acidity of anything that we did not directly measure in our investigations. 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.

For the sake of clarity, we will present the results of each of our experiments in the same order that we outlined them in part 2. We will then discuss how the results of each experiment informed the next. After that we will discuss the implications of everything we investigated along with the potential implications of an interesting discovery that we stumbled on while mulling over the outcomes of our experiments.

Baseline Brew Water Acidity

The first question that we wanted to answer was: to what degree might the acidity of different brew waters vary? So, we gathered five different types of water and tested their pH’s and tastes.

The results:

We had a feeling that there would be some variation in the pH of each water, but were surprised to see just how much! The total range was nearly 2.5 points on the pH scale with our tap water (T) being the most basic and distilled water (D) being the most acidic. You might be thinking to yourself, “Wait a minute, shouldn’t distilled water have a neutral pH of 7?”. Technically, you are correct and we had the same thought. But a little investigation showed that it is common for distilled water to register as acidic because it absorbs carbon dioxide (CO2) from the air. That C02 frees up hydrogen ions. As you know from reading part 1, an increase in the presence of hydrogen ions leads to a higher acidity measurement.

On the opposite end of the spectrum, we were curious as to why our tap water was so basic. We concluded that the basicity is more than likely due to alkaline minerals suspended in the water. Denver, Colorado, where our QC lab and roastery are located, is known to have relatively hard water. The minerals that cause water hardness generally make water basic. If you live somewhere with hard water, you may have noticed some of these minerals building up on your faucet or shower head as lime scale.  It is interesting to note that the amount of these minerals present was too low for our TDS meter to detect them, but sufficient enough to alter the pH of our water.

Another thing that caught our eye about the results of this test was the difference in pH between our tap (T) and filtered (F) waters: nearly two whole points on the pH scale! This leads us to believe that our filters are removing a significant portion of the minerals in our water. So much so that perhaps the buffering effect (tendency of substances to limit changes in acidity) of the minerals in our water is nearly eliminated causing the water to behave more like distilled water (D).

In terms of the perceived acidity of each water we were again surprised by our results. While there was a significant variation in the measured pH, the variation in how we perceived the water wasn’t as extreme. We didn’t pick up much in the way of significant taste differences, but what we did note was a difference in the mouth feel of each water. Tap water was familiar and hollow, while waters with lower pH’s felt more present. Distilled water (D) in particular had a very round, heavier, almost syrupy feel to it. Our filtered water (F), on the other hand, felt quite thin relative to the other test samples.

Given that our sample of different waters had such a wide range of pH measurements, we wondered if this variation would translate into coffee brewed with each water. This lead us to our next experiment.

Does Brew Water Affect Acidity of Brewed Coffee?

For this experiment we brewed a single type of coffee with each type of water that we tested above. We then measured and tasted each brew. 

The Results:

Kudos to Leo, our head roaster for his brew consistency shown by the tight range in TDS of +/- .025%.

Interestingly, the TDS wasn’t the only thing we found to be fairly consistent. Our measured pH’s went from having a range of +/- 1.245 pH to +/- 0.14. While there was still some variation in measured acidity, that variation occurred within a much tighter window than that of the water by itself and did not perfectly map on to the variation of our waters. That is to say, the most acidic water (distilled (D)) translated to the second most acidic brew at 5.03 pH and the most basic water (tap (T)) translated to the second least acidic brew at 5.15 pH. That said, in general, more acidic waters (D) & (F) did translate to more acidic brews (5.03pH & 4.99pH) and more basic waters (T) & (A) did translate to less acidic brews (5.15pH & 5.27pH).

In terms of the perceived acidities of each water, those that measured less acidic did indeed present less acidic on our palettes as well. The brews in which we used tap (T) and alkaline (A) waters had relatively muted acidities with much more pronounced sweetness. The brews in which we used bottled (B) and distilled (D) waters presented with a bit stronger acidity; they were brighter and left our mouths a bit stickier. The one outlier was the brew in which we used distilled water. This brew presented fairly sweet with a more faint acidity, though that which we did pick up on was a very specific, pear-like, malic acidity.

In general, these tasting results weren’t out of range for the coffee that we brewed. Courage, one of our non-CBD signature coffees, was chosen for its deep chocolaty notes and present, but not overwhelming acidity. It’s a much more approachable coffee than some of our bright, fruity, light roasted single origins.

Based on these results, it seemed to us that variation in the measured acidity of different brew waters has only a limited effect on the measured acidity of the brewed coffee that those waters are used in. However, the effect of different brew waters seems to be pretty significant for the perceived acidity of the coffee that they are used to brew.

How do the Acidities of Different Coffees Compare?

After getting an idea as to the extent to which variations in brew water acidity affect the acidity of coffee, we wanted to see what kind of variation we might find in the acidity of a handful of different coffees all brewed with the same water.

The results:

There is quite a bit to unpack here, so bear with us. First, you might notice a fairly wide range in TDS for all these coffees: +/- 0.125%. Initially, this was a little perplexing to us given that we switched to an automatic drip pot that brews with the same water temperature and “pour” every time and our grind size was fairly consistent throughout. So, we concluded that the variation in TDS was likely due to factors intrinsic to the particular beans we used as well as differences in roast parameters. Despite the variation in TDS’s, our Courage (C) had a pH of 5 here which is nearly identical to the pH of 4.99 that we observed when we brewed that coffee with the same water in the previous experiment (we used filtered water in this experiment). Based on this finding, we felt safe in assuming that TDS and measured acidity are not closely correlated and thus, variations in TDS (at least in this range) won’t affect measured acidity.

In terms of the measured acidities of these coffees, we observed a similar pattern to that which we found in the previous experiment. There was a general correlation between perceived and measured acidities. Coffees that had less acidic measured pH’s (1) & (DR) presented as less acidic when we tasted them. These coffees had creamier mouth feels and notes of milk chocolate and baking spices. The coffees that had more acidic measured pH’s (C), (K) & (2) generally presented as such. They had stickier mouth feels and more tart notes of cherry, red apple, lime and orange.

*You may have noticed that Courage (C) came in with a lower perceived acidity when brewed with the same water in the experiment above. That may partially be explained by the difference in TDS in the two experiments. As we mentioned in part 1, perceived acidity can be altered by the non-acid substances present in brewed coffee. It is possible that when we increased our extraction (TDS) in general (from 1.23% to 1.43%), we ended up extracting compounds that strengthened the perceived acidity of the brewed coffee without actually changing its measured acidity.

Interestingly, we noticed that once coffees crossed a threshold of about 5.1 pH (CO) & (RR) the perception of their acidity began to drop off. Also worth noting, “Low Acid” brand 2 came in with the second highest measured acidity out of everything that we tested and it presented as such when we tasted it. Which is not what we expected based on the branding of that coffee.

Conventional wisdom in coffee says that up to a point, acidity in coffee decreases the darker you roast the coffee. Our results in this experiment seem to support that idea. Our Dark Roast (DR) came in with the second highest pH value and presented as quite smooth and creamy. Given that one of the “Low Acid” brands (2) that we tested came in with a relatively low pH of 5.05, roast degree could be just as good an indicator of acidity as branding. The Low Acid brand 2 coffee that we used was relatively lightly roasted.

How Does This All Compare to Other Beverages?

Once we had given ourselves an idea of the range in measured and perceived acidities of hot, brewed coffee we wanted to give ourselves an idea as to how that compared to a few other common beverages. We went ahead and measured the acidity of whole milk, orange juice and a 24-hour cold brew of our Courage coffee.

The results:

All of our hot, brewed coffees came in with a pH of between 5 and 5.5. Given that coffee is commonly referred to as a particularly acidic beverage we found it interesting that orange juice is actually much more acidic with a pH of 3.67. It also took us by surprise that whole milk technically counts as an acid because its pH of 6.64 is below the neutral 7. We have also come across many sources that claim cold brewed coffee is generally less acidic than hot brewed coffee because of differences in the way that colder water extracts compounds from the grounds compared to hot water. Our results upheld this idea with our cold brew having a pH of 5.37 (compared to 5 when the same coffee was brewed hot). We also noticed that our cold brew tasted much smoother than its hot counterpart. The acidity was more subdued and the depth and sweetness of the coffee much more pronounced.

Takeaways

While the activities that we carried out are by no means an exhaustive or perfect investigation of the myriad of factors that may affect coffee acidity we do think that there are some worthwhile lessons to be learned.

  1. Brew water does have an effect on the acidity of the coffee you brew with it. More basic waters are likely to lead to less acidic coffee.
  2. Brew method is equally important. Cold brew is noticeably less acidic.
  3. Roast degree may have an impact on brew acidity that is just as significant as brew water and brew method. The darker roasts that we tested brewed noticeably less acidic.

Bonus

While talking about alkalinity and brew water we were reminded of an article by Scott Rao that we had read a while back that talked about lime scale in the vessel that you are using to heat your water before brewing. The article boils down (no pun intended ;)) to the idea that when you use the same vessel (tea pot, electric kettle, automatic drip brewer, espresso steam boiler, etc...) to heat water over and over again, each time you use that vessel, the water that you boil leaves behind a little bit of its minerals. Eventually a significant amount of those minerals build up and you are left with lime scale (remember the stuff built up on your shower head). That lime scale in your heating vessel will alter the acidity of water that you warm in that vessel and after a while it can have a big impact. Even if you can’t see the lime scale, it will make your water much more basic.

We wondered, how much more basic? Well, more than a whole point on the pH scale. Our filtered water measured 6.7 pH before being boiled. After going through our electric kettle the water came out with a pH of 7.66. The effect our automatic drip pot had was even stronger. The water that was boiled there came out with a pH of 8.15. This leads us to wonder how our results may have differed if our water heating vessels were completely free of lime scale. That said, we used the same vessel for each run of each experiment, so the effects of the vessel should have been uniform across all of our water/coffee samples.

Thanks for checking out this series, we hope you enjoyed! We’d love to hear from you if you have questions, insights or anything else to share regarding this series! 



 






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