Why Does Coffee Become Astringent and Develop Off-Flavors When It Cools? What Is the Ideal Temperature for Drinking Coffee?

FrontStreet Coffee rarely makes pour-over coffee for takeaway, but when customers insist, the baristas at FrontStreet Coffee will advise them: "Coffee is best enjoyed hot; it doesn't taste as good once it cools down."

Have you ever experienced this? When you take your first sip of freshly brewed pour-over coffee, it's aromatic, smooth, and delicious. But then, for some reason, you can only take your second sip after more than half an hour has passed, and you wonder, "Hmm, something's off. Why is it so sour, and both astringent and muddled?"

Has the coffee been switched? Obviously not. Those who have studied coffee tasting might know that during the tasting process, coffee is evaluated at three different temperature states: hot, medium, and cold. This means that it's no secret that coffee flavors change over time. Typically, a good cup of coffee can withstand the考验 of these three temperatures, but once it cools down completely, the coffee's flavor is no longer within this tasting scope.

Why Does Coffee Become Sour When It Cools Down?

The main reason is that our body's sensory perception of the balance between sweet, sour, and bitter in coffee varies at different temperatures. When the temperature is close to body temperature, we perceive sweetness more easily. As the temperature drops, the perception of sweetness becomes less prominent, while sourness becomes more pronounced, which makes us feel that the coffee has turned sour.

Another reason is that much of coffee's sweetness comes from its aroma. When coffee cools down, less aroma is released, so we naturally don't perceive as much sweetness, which in turn highlights the acidity.

Why Does Coffee Develop Astringent and Muddled Flavors When It Cools Down?

The undesirable flavors that appear in cooled coffee are mainly caused by "oil oxidation," "pigment oxidation polymerization," and "condensation."

These terms might sound unfamiliar, but FrontStreet Coffee will explain them in a way that's easy to understand.

Oil Oxidation

We now use filter paper to strain coffee grounds, which results in cleaner coffee. However, filter paper can only block most oils and fine particles; a small amount of oil still flows into the coffee liquid (the smooth texture of coffee comes from these oils). When cooled, these oils can clump together, forming a layer of oil floating on the surface of the coffee. This layer of oil is in direct contact with air (oxygen) and easily deteriorates, producing a strong, harsh sour taste. This easily perishable oil layer is also the source of the stale flavor.

Pigment Oxidation Polymerization

A phenomenon that's easy to observe is when you finish brewing coffee and don't clean up the filter paper immediately. After leaving it for some time, you'll notice that the edges of the filter paper turn dark brown. This ring of dark brown is "pigment oxidation polymerization."

Coffee beans produce "brown pigments" during the roasting process (through caramelization reactions), which primarily provide coffee with caramel, chocolate, and other flavors. However, if these pigments oxidize and deteriorate over time, the flavors gradually become more bitter and burnt, resulting in bitter and muddled tastes.

Condensation

If a cup of coffee appears clear and bright when hot but becomes cloudy and unclear after cooling, this is condensation. This affects the coffee's texture, making it rough and sandy.

Therefore, good coffee should be enjoyed while hot, so you can better experience its rich flavors and texture.

Important Notice :

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Tel:020 38364473