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The Difference - Sourness & Acidity

December 14, 2013

As mentioned in the last post, we are currently working on a water project that will become a little book. Part of that process is the inspiration for this article. During the project we organised blind taste testing sessions, and we drew up our own scoring sheet for participants to use. We did this in order to split up a few specific sections and try to achieve more objective and quantifiable results in relation to the tests we were doing.

Below is a link to one of the graphs that displays the sensory results of one coffee blind scored across three different waters - A, B and C.

Before testing began, I instructed the tasters to mark acidity in terms of how positive it was, i.e. that if the coffee has a lot of desirable acidity then mark high and to mark low for vice versa, for sourness I told them to mark this section in terms of intensity, low for little to no sourness and high for very sour

Coffee1_A,B,C (2)

As you can see, tasters responded quite differently to the same coffee when made with different waters, but what is of particular interest here, is the comparison between the sour and acidity columns for each water.

I think that the more useful and relevant the language when assessing and describing flavour experiences, the better. Often this just means using two terms rather than one, so they can complement and contrast each other. In essence two assessments are needed when one piece of terminology won’t do the job. I think “acidity” and “sourness” are a prime example of this.

A common statement is as follows - "sourness IS acidity"

When marking acidity on coffee we are not marking the sourness of the coffee, even though types of acidity can contribute to sourness. We are instead marking a quality that (if one is not familiar with as regards speciality coffee) could be misinterpreted as denoting sourness.
Although it’s possible for a coffee to have high acidity and also be sour, this doesn't mean they are mutually exclusive. For instance, a creamy, nutty and floral coffee could have wonderful acidity; acidity that may be crisp, juicy, or sparkling. Here the coffee does not display much sourness but has great acidity.

This may sound a bit obvious but I think it’s worthy of a little exploration and this graph and the taste test we did were, I think, a good direct example of this topic rather than my more philosophical ramblings on the same topics in blogs such as – ‘Why Coffee Isn't Overly Acidic’ (In hindsight, the wording " Isn’t Overly Sour and Acidic" would have been a more accurate title) and “taste, flavour and perception”.

If you study the sourness and acidity results, they actually display the most opposing results out of all the sections. In that water B has the best acidity, closely followed by water A, but when we then move over to the sourness column, water B displays almost half the sourness score that A does.

This means that water A, although displaying a high, positive acidity also displayed high sourness; whereas Water B wins out on acidity but is accompanied by much less sourness. When we consider the other scoring sections we can deduce that water A brewed/produced a cup with good acidity but was also quite a sour driven cup. Whereas water B brewed/produced high/good acidity along with a more balanced and complex cup.

The breaking up of sourness and acidity was particularly useful for this test, if we only used acidity to mark the coffee, then A and B would have appeared closer in this area, but the sourness marker shows how different they really were.

It’s useful to also note that water C displayed abysmal acidity but comparable sourness to water B. This can then help infer that water C most likely displayed a dull heavy sourness, with little desirable acidity.

I find the interplay of these two markers fascinating as they rarely seem to match up and together I think they've told us more about what people were tasting on the day and how exactly the waters affected the same coffee. I wanted to share this graph as I think it nicely displays the independence of acidity and sourness in coffee.



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