It's been standard knowledge in coffee science since the 1970s that the pH readings are misleading due to the buffering effect of other solubkes in the coffee. For instance, Robusta and Arabica have roughly the same pH. Turns out, your tongue is much more accurate than a test strip, since the titrable acidity corresponds very well with people's perceptions of acidity.

Cold brew is outselling regular brewed coffee, because unlike hobbyists and professionals, most coffee drinkers dislike acidity. If I wanted to be the next Starbucks, I'd sell only small lot, organic, peasant and animal friendly Robustas, these, of course, being far more deserving and discerning than mere agrobusiness Arabicas.

baldheadracing wrote:From the source article abstract:

As I failed organic chemistry, I can only defer to the authors' interpretation of their results. I linked to Perger as he seemed to have dumb-downed the article, no doubt making errors of omission that I cannot grasp.

I'll try to clear up the findings from this study for those interested. The authors are using two metrics for measuring acidity of coffee - pH and 'Titratable Acidity'. pH is the standard way of measuring acidity and is a measure of the concentration of protons present in a solution (by definition, acids have protons that they break away from in solution). Titratable Acidity is a measure of the amount of NaOH that is needed to reach a desired pH. The authors cite other studies that indicate that Titratable Acidity is a better metrics for measuring sourness than pH, but this isn't their main reason for measuring it.

For an extreme example of how these two metrics can differ, consider two solutions: (i) acetic acid dissolved in a buffer and (ii) hydrochloric acid dissolved in the same buffer. Let's assume that the two solutions measure the same pH. If that's true, then we know that there must be very different concentrations of each acid in solutions (i) and (ii) due to differences in the amount of protons given off by the acids (i.e. the "strength" of the acid). If we add NaOH to each solution until we get to a given pH (say pH=6), the volume needed to reach this point will differ for the two solutions. This is a case where pH is the same, but Titratable Acidity is different.

The cited study finds that the pH of hot and cold brew coffee are the same, but the Titratable Acidities differ. From this, the authors conclude that there must be different acids present at different concentrations in hot and cold brew.