Acids in coffee: can we actually taste the difference?

acids in coffee tasting

In coffee, like in wine, acids are key to our perception of a wide variety of flavours. Can we actually taste the difference between them? Matt Brown from our Coffee Science and Education Centre puts this to the test.

Our everyday interaction with flavour is a complex one. We get passionate over our beliefs on quality, however when asked to identify the flavours we are tasting, a common response is, ‘I know what I like, but I don’t know how to describe it.’ This is especially true for coffee, where there isn’t a strawberry or apple sticking out of the cup to give us a visual clue. It’s the associated memories of these flavours we have to seek out, and for this it takes training.

With all the technology in the world today, the best method to analyse coffee’s quality is still through taste. The method used is called cupping; the practice of grinding roasted coffee into a bowl, sniffing it, adding water, slurping it as loud as you can, and attributing the flavours you taste with a score. One of the benchmark sensory protocols used in cupping is called the Q arabica. This requires a participant to pass more than 20 sensory modules, from identifying aromas, organic acids, and mixtures of sweet, salty and sour tastes. Certified as a Q grader or not, the act of cupping will yield complex flavour descriptions, such as we’ve found in our own cuppings:

  • I love the phosphoric acidity in bowl #4, it tastes like cola.
  • I agree, but the malic acidity in bowl #7, it reminds me of a freshly picked fuji apple.
  • Yes, but the strong citric acid in bowl #3 is so sweet, it’s like grapefruit with sugar on top.

Many of the common descriptions you’ll find when cupping specialty grades of coffee are fruit flavours. Recently, some of our team attended presentations that show conflicting evidence to suggest whether or not people can taste individual acids, especially when mixed with coffee.

So what did we do?

What we at CSEC always do…. Get some numbers!

acids in coffee samples

The tasting panel: Hey, who wants to taste some acids?

We put together a small panel of tasters, comprising of a mix of consumers, certified Q graders, roasters and baristas. We made them taste citric, malic, acetic, phosphoric and quinic acids, diluted in water – and the same acids again in filter coffee. We sourced these from ‘the coffee professor’. The acids are at a concentration of 1mol/L, and we have been assured they are safe to drink…

The team were not aware what array of acids we were testing for the acids in water. They were just asked to describe a flavour associated to the bowl they were tasting.

In addition to positive identification of the acid, we also asked the tasters to arbitrarily give an intensity rating out of 5.

The Samples

The panel tasted the individual acids diluted to 3 micrograms acid per gram of water and 6 micrograms/g water (for reference, 1 microgram = 1 millionth of a gram). We used treated brew water, which was tap water run through a filter with a carbon block and ion exchange resin, to suit SCA standards.

The panel then also tasted the 6 microgram acid/gram water solution in brewed coffee. We used our Belaroma Julius blend, which is a medium espresso roast, brewed with 55g roasted, ground coffee to one litre of water. To calibrate the tasters, they were given the same concentration of acid in filtered water with the acids labelled. They were then given the task of matching this acid to the coffee sample spiked with the same acid.

The results: can we identify acids?

acids in coffee graph_figure 1

Figure 1: A) Taste results from 3microgram acid/g water, Figure 1: B) 6 microgram/g water C) Coffee with 6 micrograms of acid/g coffee added

What we can see is that acetic acid was more readily identified (67% of tasters correctly identified it as vinegar), and that citric acid was detectable by 50% of tasters (who identified it as lemon). At higher concentration, as expected, acetic acid was more readily identified, as was citric acid.

In terms of intensity, the tasters rated Citric, followed by Malic as the most sour. Acetic was the least intense, even though it was the easiest to ID.

From the above results, it seems that acetic acid and citric acid are the most readily identifiable. Acetic acid might be easier to identify as it also has a volatile component, that can be detected by nasal olfactory senses.

acids in coffee cupping

Acids in Coffee vs Acids in Water?

 When it came to the coffee samples, citric was the most readily identified acid. It was identified correctly in the same frequency as in the acids in water test for the same concentration. As it was a small sample size, this is likely to be coincidental.

In both the coffee & water samples, Quinic and Phosphoric acids remain the needles in the haystack. Very hard to find, even with the honed palettes of the Q graders!

Another point to note, is the people who correctly identified the acetic and citric acids, said they did so by the comparative flavour, and the Malic acid, by the comparative texture to the standard in the bowl of water. So, we tend to ‘feel’ malic acid, rather than ‘taste’ it.

One of the most interesting findings from this study is that acetic acid was detected by fewer panel members in coffee than when it was pure in water. It is likely that the aroma of the coffee overpowers the aroma of the acetic acid at this concentration.  So, a potential outcome of this is that if you accidentally spill some vinegar in your coffee, you’re unlikely to notice it!

The person who identified most samples correctly in this instance, was not a Q grader, but a humble Barista. Clearly showing that tattoos, piercings and ear spacers increase your ability to taste.

Conclusion

To answer the question, can we taste specific acids in coffee? For acids in water, the answer is, yes, most of the time for acetic and citric.

As for acids in coffee: aside from citric acid, we don’t think so!

So, the next time you’re at a cupping, surrounded by Q graders or not, and someone describes how delicious that malic acidity is, you can say, ‘I don’t remember adding any Lysergic acid diethylamide to this bowl, but perhaps you mean this coffee reminds me of apples’.


For more on the work of the Coffee Science & Education Centre, click here. To find out more about professional training, view our courses.


 

Matthew Brown
Matty’s love of coffee started at a young age and exploded the moment his mind was exposed to the science that makes great coffee possible. Motivated by the endless possibilities of what coffee could be, Matty is in his element researching, exploring and implementing new ideas that help shape the next chapter in the evolution of the speciality coffee industry. Matty’s deep and extensive coffee knowledge continues to shape our Barista Training & Education Programs, and he is a key knowledge source influencing continuous coffee improvement within the business. On the rare occasion Matty’s head is not in the books, he can be found savouring in other molecular gastronomic delights, writing, tickling the ivories or singing up a storm.