From time to time, people come in to the Roastery to purchase some coffee beans and who are concerned with the acidity in the beans and the effect on their stomachs. They ask for a low acid coffee. Easy enough, until you start thinking about the acids and what the individuals really may be looking for.
6% of the compounds in a roasted bean are acids. We find citric acid, acetic acid and malic acid as the most important acids that affect flavor (sourness), and we also have quinic, formic, phosphoric, chlorogenic and other acids, which do not affect the acid taste as much, but do contribute. By acid taste, I mean the tingle on your tongue, especially present when you drink a lighter roast. The darker roasts tend to remove the acid taste and have more body, or weight on the top and sides of your tongue.
The acid taste, however, is not necessarily the same acid that may affect your stomach. Some people have found that the malic acid present would be the culprit. Others suppose that it is actually some combination of particular acids that are interacting with the chemistry going on in individual stomachs. In our beans, we have citric and acetic as the main contributors to taste, with malic and phosphoric only at half the threshhold levels.
When I say, ‘our beans’, I mean Arabica and not Robusta. The Arabica beans actually have less acids present as a green bean than the green Robusta. Once roasted, however, the proportion of free acids available changes and Arabica will tend to have more than Robusta. Perhaps this is a contributing factor to why Arabica taste so much better than Robusta, on the whole.
People declare, ‘this coffee is stomach-safe’. Often the Indonesian coffees have been given this status, primarily because they tend to be naturally processed as opposed to wet processed. The dry process (natural) will subdue some of the acid. Some people also think that the more oily the bean, the higher the acid (the ones that affect the stomach). We know that the citric and acetic are less present with an oilier bean – oils develop at darker roasting temperatures.
There’s a lot of possibility presented here, and we haven’t even touched on organic versus conventional poetntial. Basically, there’s no succinct answer to, ‘can I have a low-acid coffee’, especially without knowing if they mean taste or effect. The easiest thing would be to turn people on to the darker roasts and the Indonesians, like a Sumatran on Papua New Guinea. Still, there may be some level of malic acid present that would cause gastric concern. There may also be something in the person’s own chemistry that disagrees with certain coffee. The acidic taste would be replaced with the higher body.
That’s all for Part I. I’ll write more about the chemistry of coffee in the future.