是什么导致咖啡的涩味？

被称为多酚的大分子，尤其是绿原酸（CGA）和丹宁酸，是冲煮咖啡中涩味的可能主要来源。多酚是大分子，与大多数其他咖啡可溶物相比，提取起来往往较不容易，尽管CGA似乎比单宁提取时更容易提取。（尚未科学证明CGA比单宁更容易提取，但似乎很可能。）很可能通过 渗滤式冲煮 冲煮的咖啡液提取物中发现了大多数收敛性多酚。由于缺乏 通道作用，浸泡式萃取 不太可能出现涩味。

是什么增加了冲煮出涩味的风险？

冲煮咖啡中涩味增加的几种潜在来源：

• 生豆里面有未生长成熟的咖啡豆

• 烘焙发展不足

• 渗滤冲煮（手冲）过程中的通道效应

未生长成熟的咖啡豆和发展不足的烘焙都倾向于在杯中产生更高程度的CGA。CGA既是收敛性多酚，也是咖啡中最普遍的酸。一杯适量的CGA对于一杯美味的杯子可能很重要（尽管我不确定我们是否有人尝过没有CGA的咖啡），但是当CGA含量太高时，咖啡会变得很涩。

如何找到并修正涩源

当我发现冲煮有涩味时，我将通过一系列步骤来查找和修正涩味的来源：

• 如果我曾经用同一批烘焙的咖啡豆做出过没有涩味的 渗滤式冲煮（手冲），则几乎可以肯定最近的出品有涩味是由 通道效应 引起。在这种情况下，我会（希望）使用更好的磨豆机进行较粗研磨（相比这次）进行再次冲煮。

• 如果我不能排除 通道效应 的原因（例如，如果我不相信自己的冲泡方法或技能），我会对咖啡豆进行杯测。如果杯测有涩味，则 通道效应 不是 手冲 出现涩味的原因，或者至少不是唯一的原因。

• 如果 渗滤式冲煮 和 浸泡式冲煮（杯测）都产生涩味，则原因必须归因于烘焙的发展不足或未成熟的咖啡豆。

• 如果所涉及的咖啡的某些烘焙批次具有涩味，而其他批次则没有，则很可能是由烘焙过程的发展造成涩味的原因。

• 如果杯测完所有烘焙批次的豆子都有涩味，并 相信不是有烘焙的发展不足造成，那么 生豆 里面可能有未生长成熟的咖啡豆。

原文

WHAT CAUSES ASTRINGENCY IN COFFEE?

Large molecules called polyphenols, in particular chlorogenic acids (CGAs) and tannins, are the likely, primary sources of astringency in brewed coffee. Being larger molecules, polyphenols tend to extract less readily than most other coffee solubles, though CGAs seem to extract more readily than tannins do. (It has not been scientifically proven that CGAs extract more readily than tannins do, but it seems probable.) It’s likely the majority of astringent polyphenols found in brewed coffee extract via channeling in percolation brewing. Astringency is much less likely to occur in immersion brewing due to the lack of channeling.

WHAT INCREASES THE RISK OF AN ASTRINGENT BREW?

There are several potential sources of increased astringency in brewed coffee:

• beans (seeds) from underripe cherry*

• underdevelopment in roasting*

• channeling during percolation brewing

*Both underripe cherry and underdeveloped roasts tend to yield higher levels of CGAs in the cup. CGAs are both astringent polyphenols and also the most prevalent acids in coffee. Having some CGA is probably important for a delicious cup (though I’m not sure any of us have ever tasted a coffee without any CGAs), but when the CGA level is too high, the coffee becomes noticeably astringent.

HOW TO FIND AND FIX THE SOURCE OF ASTRINGENCY

When I find a brew astringent, I go through a series of steps to find and fix the source of the astringency:

• If I have previously made a non-astringent, percolation brew of the same roast batch of the coffee in question, it is almost certain that channeling caused the astringency in the more recent brew. In that case, I would brew again with either (hopefully) better technique of a coarser grind setting.

• If I cannot rule out channeling (for example, if I don’t trust my brewing method or skill), I will taste the coffee as a cupping.  If the cupping is astringent, then channeling was not the cause, or at least not the only cause, of the astringency in the percolation brew.

• If both percolation and immersion (cupping) produced astringency, the cause must be due to an underdeveloped roast or underripe cherry.

• If some roast batches of the coffee in question are astringent and others aren’t, it is likely that roast development was the cause of the astringency.

• If all roast batches of the coffee are astringent when cupped, and you are confident they are not all underdeveloped, then the green was likely from underripe cherry.

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