剛烘豆變苦的真相：二氧化碳讓萃取不均 Why Freshly Roasted Coffee Tastes Bitter: How Carbon Dioxide Disrupts Extraction
目錄：
1. 第一個關鍵是二氧化碳干擾萃取
2. 第二個關鍵是風味仍在尖銳期
3. 那要怎麼解？建議的做法是養豆
剛烘好的豆子，沖起來忽然多了苦味，很多人第一反應是：「是不是烘壞了？」其實多半不是。剛出爐的咖啡豆正處在一個很特殊的階段：排氣太強＋風味尚未穩定。你用平常熟豆的沖法去對待它，很容易把萃取拉到「不該萃的那一段」，苦、乾、粗澀就被放大了。
When freshly roasted coffee suddenly tastes more bitter, many people’s first reaction is, “Was it roasted incorrectly?” In most cases, the answer is no. Freshly roasted beans are in a very particular stage: excessive degassing combined with unstable flavor development. If you brew them using the same approach you use for well-rested beans, it’s easy to push extraction into a range it shouldn’t reach—amplifying bitterness, dryness, and roughness.
第一個關鍵是二氧化碳干擾萃取。
烘焙會在豆子內部累積大量氣體，剛烘好時最旺盛。當熱水接觸咖啡粉，悶蒸會像漢堡膨起來般劇烈冒泡，這些往外衝的氣體會形成「氣體屏障」，把水推開，讓熱水不容易均勻滲透進每一顆粉粒。於是水會自己找出路，只走少數幾條通道，這就是常說的通道效應。結果就是：水流經的地方被過度萃取，釋出苦、乾、澀；水沒流到的地方萃取不足，留下酸薄、空。兩種味道混在一起，就會讓整杯看起來「又苦又雜、不乾淨」。
The Number One Key Is Carbon Dioxide Interferes with Extraction
Roasting causes a large amount of gas to build up inside the beans, and this gas release is most intense right after roasting. When hot water first contacts the grounds, the bloom can swell dramatically, bubbling vigorously like a hamburger patty puffing up. The escaping gas forms a kind of “gas barrier”, pushing water away and preventing it from penetrating the grounds evenly. As a result, water finds its own paths of least resistance and flows through only a few channels, what we commonly call channeling. The outcome is uneven extraction. Areas the water flows through are over-extracted, releasing bitterness, dryness, and astringency. Areas the water misses are under-extracted, leaving sharp acidity and a thin, hollow taste. When these flavors combine, the cup tastes bitter, muddled, and lacking clarity.
第二個關鍵是風味仍在尖銳期。
剛出爐的前三天，香氣常常很強，但風味結構還沒融合，酸甜不夠圓潤；加上烘焙後殘留的揮發性物質尚未穩定，容易出現咖啡圈常說的「火味、燥感」，喝起來舌面乾乾的、帶煙燻苦，原本的花香果甜反而被蓋住。深焙或發展較多的豆子，這種刺激感通常更明顯。
因此，原本習慣的沖法，在新鮮豆身上很可能等同「過萃」。同樣的研磨、水溫、時間，因為粉床被排氣撐起、水流路線變得不平均，尾段苦澀更容易被拉出來。尤其當使用偏濃的粉水比(例如 1:11~1:13)，苦味會被放大得更直接。再加上細粉、較高水溫、拉長時間或攪動太多，等於把「苦味的兩個按鈕」一次按滿，木質感、焦糖化後段、烘焙苦味就會更明顯。
The Second Key Is Flavors Are Still in Their Sharp, Unsettled Phase
During the first few days after roasting, aromas can be very intense, but the overall flavor structure has not yet integrated. Acidity and sweetness are not fully rounded, and volatile compounds left from roasting are still unstable. This often leads to what coffee professionals describe as “roasty,” “burnt,” or “dry” notes, a tongue-drying sensation with smoky bitterness that masks the bean’s natural floral and fruity sweetness. This harshness is usually more pronounced in darker roasts or beans with greater roast development.
Therefore, familiar brewing methods can cause over-extraction. Because degassing lifts and disrupts the coffee bed and alters water flow, a brewing recipe that works perfectly for rested beans can effectively become over-extraction when used on very fresh coffee. With the same grind size, water temperature, and brew time, bitterness is more easily pulled out toward the end of extraction. This effect is amplified when using stronger brew ratios (such as 1:11–1:13), where bitterness becomes more direct and obvious. Also, plus fine particles, higher water temperatures, longer brew times, or excessive agitation, and it’s like pressing all the bitterness buttons at once, bringing out woody notes, caramelized roast flavors, and harsh roast bitterness.
那要怎麼解？建議的做法是養豆：
給它時間排氣、讓風味變圓融。大致可抓：深焙 3~5 天、中焙 5~7 天、淺焙 10~14 天(極淺焙甚至可能要 2~3 週才到高峰)。如果你現在就一定要喝，沖煮端可以先「溫柔一點」：悶蒸延長到 40~60 秒、把水溫降個 2~4°C、縮短總時間並減少攪動，必要時尾段提早停。真的太新鮮又想喝得乾淨，還有一個極端但有效的方法：先磨粉靜置 15~20 分鐘再沖，香氣會少一點，但苦澀通常會退得很有感。
理解新鮮豆的特性，就會發現：剛烘豆不是「不好喝」，而是它需要一點時間與更合適的沖煮節奏。把氣排掉、把萃取變均勻，甜感和香氣自然會回來。
How to Solve It? The Solution: Rest the Beans (Degassing)
The most effective solution is simply to give the coffee time to rest, allowing excess gas to escape and flavors to become more cohesive. As a general guideline: Dark roast: 3–5 days, medium roast: 5–7 days, light roast: 10–14 days, very light roast: sometimes 2–3 weeks to reach peak flavor. If you need to brew very fresh beans right away, adjust your brewing approach to be gentler: Extend the bloom to 40–60 seconds, lower the water temperature by 2–4°C, shorten total brew time and reduce agitation, and if needed, stop the brew slightly earlier. For an extreme but effective method when beans are extremely fresh and you want a cleaner cup: grind the coffee and let it sit for 15–20 minutes before brewing. You’ll lose some aroma, but bitterness and harshness often decrease noticeably.
Understanding the nature of freshly roasted coffee reveals that it’s not “bad”—it simply needs time and a more suitable brewing rhythm. Once excess gas dissipates and extraction becomes more even, sweetness and aroma naturally return, and the cup becomes balanced and enjoyable again.
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