Why Does Dark Roast Coffee Have Acidity? What's the Difference Between Dark and Light Roast Coffee? Where Does Coffee's Acidity Come From?

FrontStreet Coffee has discovered that many friends hold certain misconceptions about dark roast coffee, such as believing that dark roast coffee is completely acidity-free. The story began yesterday when a friend shared with FrontStreet Coffee that he tasted acidity in a cup of dark roast coffee. Since this greatly contradicted the theoretical knowledge he had encountered, he was quite shocked when he tasted the acidity,一度认为是那家咖啡店的豆子烘的不够深。

The Relationship Between Roast Level and Acidity

"When coffee is roasted lighter, it tastes more acidic; when coffee is roasted darker, it tastes more bitter" – this is a phrase that many friends have heard repeatedly. The reason why most friends misunderstand dark roast coffee is precisely because of this statement. This statement itself is not wrong, but it easily leads to the misconception that "dark roast coffee is completely acidity-free." Dark roast coffee does have acidity, it's just relatively less noticeable.

Where Does Coffee Acidity Come From?

The sources of acidity in coffee can be divided into two categories: native organic acids and roasting-generated acids. Native organic acids refer to organic acids that already exist in raw coffee beans, such as chlorogenic acid, citric acid, malic acid... Roasting-generated acids refer to acetic acid (vinegar acid) produced during the roasting process through caramelization reactions of sugar substances.

Why Dark Roast Coffee Contains Acidity

In an article a couple of days ago, FrontStreet Coffee mentioned that organic acids in raw coffee beans gradually decompose and transform during the roasting process. The lighter the roast level, the less decomposition and transformation of organic acids; the deeper the roast level, the more transformation occurs. Organic acids are one of the important sources of acidity in coffee. This explains why lighter roasted coffee is more acidic and darker roasted coffee is more bitter. Because when coffee is roasted darker, the decomposition of organic acids reduces acidity. However, this does not mean that dark roasted coffee is completely acidity-free. Because organic acids do not decompose completely, even after coffee is roasted to the second crack, there will still be small amounts of organic acids present in the coffee contributing to acidity. At the same time, the acidity in coffee is not entirely provided by organic acids! Sugar substances in coffee are converted to acetic acid through caramelization reactions during the roasting process, and acetic acid gradually increases with deeper roast levels.

Why Acidity in Dark Roast is Difficult to Detect

Therefore, we can understand that the acidity in coffee does not disappear due to deeper roasting; it just becomes a smaller proportion in the coffee. But under normal circumstances, we cannot taste obvious acidity from dark roast coffee because the acidity in dark roast coffee is masked by a "smokescreen"!

Why is the acidity in dark roast coffee not easily detected? Under deep roasting, coffee develops a strong bitter taste brought by carbonized substances and caramelization products. Compared to acidity, human perception of bitterness is more sensitive, not to mention that the amount of bitter substances is not small, so the trace amounts of acidity in coffee are masked. Furthermore, after deep roasting, coffee has characteristic aromas such as smoky and chocolate. Because aroma dominates olfaction and prioritizes our associations, it further weakens the perception of acidity.

In summary, we can understand why it's difficult for us to taste obvious acidity from dark roast coffee. It's both because the acidity itself is less, and because the acidity is masked by the bitterness and aroma of dark roast coffee.

Why Some People Can Taste Acidity in Dark Roast Coffee

If you taste acidity from dark roast coffee, it might be caused by these situations. One reason is that this coffee itself belongs to a coffee with relatively "high acidity content," so even after deep roasting, it still retains detectable acidity; or it could be because this coffee has under-extraction, where the dissolved substances are not sufficient to completely mask the acidity, giving you the opportunity to capture the coffee's acidity.

Of course, it's also possible that your senses are more sensitive, allowing you to detect even subtle acidity~

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