中焙手沖TDS偏低的三大關鍵：低溫悶蒸、粗研磨、走水捷徑 Three Key Reasons Medium-Roast Pour-Over Coffee Shows Low TDS: Low-Temperature Blooming, Coarse Grinding, and Water Bypassing
很多人以為中焙「更好萃、喝起來應該更濃」，但實際手沖時卻常見：香氣明確、甜感也在，入口卻偏薄，量測TDS甚至偏低。關鍵在於中焙並不等於濃度保證。真正左右濃度與厚實度的，是萃取動能與粉床中的水流路徑。曾有一組條件看似不淡：22g / 320g（1:14.5）、研磨950µm、溫度82-92-92-82°C、總時間2:40，卻量到TDS約1.0。這通常不是豆子「不濃」，而是三個地方同時把萃取壓低。
Many people assume medium roasts are “easier to extract” and should naturally taste stronger. In practice, however, pour-overs often show a different result: the aroma is clear, sweetness is present, yet the cup feels thin, and measured TDS can be low. The key point is that a medium roast does not guarantee higher strength. What truly determines concentration and body are extraction energy and the water flow paths within the coffee bed. For example, one brew that looked far from weak: 22 g / 320 g (1:14.5), 950 µm grind, temperatures of 82-92-92-82°C, total time 2:40, still measured around 1.0 TDS. In most cases, this isn’t because the coffee is “weak,” but because three factors simultaneously suppress extraction.
三個關鍵點
第一個關鍵：
低溫悶蒸讓萃取啟動不足。悶蒸不是只看秒數，而是要讓粉床充分浸潤並均勻開始溶解。當悶蒸用到82°C，溶解速率會下降，浸潤更容易不完整；接著進入主段注水時，水更可能沿著阻力小的地方通過，造成接觸不足。會看到時間「有到」，但有效萃取不足，TDS與杯感都容易偏薄，尾韻也可能更散。
第二個關鍵：
粗研磨與低溫疊加，讓可溶物釋出速度跟不上。950µm對中焙來說偏粗一點點。粗研磨本來就需要更高的水溫、較穩定的水柱與更好的浸潤來補足萃取動能；若又搭配偏低的溫度起手，常見結果是「香氣在、甜感輪廓有，但甜的密度與厚度起不來」，喝起來容易覺得清、薄、支撐感不夠。
第三個關鍵：
走水捷徑讓萃取分佈不均，濃度數字不一定大變，但厚實度會先掉。粉床裂開、邊緣固定沖刷痕、下滴忽快忽慢，都可能代表水在走捷徑。此時杯中會出現「局部萃過頭」與「大面積萃不足」同時存在：風味可能仍清楚，但結構不緊、口感不厚，尾韻容易空或偏尖。
Key Factor 1
Low-temperature blooming leads to insufficient extraction activation. Blooming isn’t just about time; its purpose is to fully wet the coffee bed and initiate dissolution evenly. When blooming at 82°C, the dissolution rate drops and full saturation becomes harder to achieve. As main pouring begins, water is more likely to follow paths of least resistance, reducing contact with large portions of the grounds. The brew time may look “complete,” but effective extraction is lacking, resulting in lower TDS, a thinner mouthfeel, and a more diffuse finish.
Key Factor 2
Coarse grinding combined with low temperature slows the release of solubles. At 950 µm, the grind is slightly coarse for a medium roast. Coarser grinds already require higher water temperature, steadier flow, and better saturation to provide sufficient extraction energy. When paired with a low-temperature start, the common outcome is: aroma is present, sweetness is outlined, but sweetness lacks density and body. The cup tastes clean and light, yet thin and under-supported.
Key Factor 3
Water bypass creates uneven extraction; body drops before TDS does. Cracks in the bed, fixed erosion marks along the edges, or irregular dripping speeds all indicate water bypass. In these cases, over-extraction occurs locally while large areas remain under-extracted. The overall TDS may not change dramatically, but structure and body suffer first. Flavors can still be clear, yet the cup feels loose, thin, with a hollow or sharp finish.
悶蒸溫度測試
為了更清楚看出「悶蒸溫度」如何影響厚薄與風味比例，我們加入一支測式豆：哥倫比亞 考卡省 鷹颯小農精選 水洗（杯測：柑橘、麥芽糖、堅果）。條件固定：20g、研磨950µm，注水節奏固定 50/160/260/320g，時間點固定 00:50/01:20/01:50/02:50移開濾杯，僅改變悶蒸溫度。
實驗A（82-92-92-82°C）：
悶蒸50秒，2:50移開，得267g咖啡液，TDS 1.16。風味：焦糖、橙皮、尾韻柑橘，但「不夠厚實」。
實驗B（92-92-92-82°C）：
其他條件不變，僅悶蒸改92°C，得275g咖啡液，TDS 1.17。風味：焦糖、苦巧克力、尾韻堅果焦糖，「更厚實」。
To isolate the effect of bloom temperature, we tested a reference coffee: Colombia, Cauca – Smallholder Selection, Washed (Cupping notes: citrus, malt sugar, nuts). Fixed conditions: Coffee: 20g, Grind: 950µm, Pour schedule: 50/160/260/320g, Timing: 00:50/01:20/01:50 remove dripper at 2:50. Only the bloom temperature was changed
Test A (82-92-92-82°C)
Bloom: 50 seconds, Yield: 267g, TDS: 1.16. Flavor: caramel, orange peel, citrus finish, but lacking body.
Test B (92-92-92-82°C)
All variables identical except bloom at 92°C. Yield: 275g, TDS: 1.17, Flavor: caramel, dark chocolate, nutty-caramel finish, noticeably fuller and more structured.
這組對照最有價值的結論是：TDS只差0.01，厚薄卻能差很多。原因在於悶蒸溫度優化後，粉床浸潤更完整、萃取分佈更均勻，甜與褐色系（麥芽糖/堅果/可可）的比例更集中，所以即使濃度幾乎相同，口感會更緊、更實。反過來，中焙豆的低溫悶蒸更容易讓萃取啟動不足，風味輪廓偏向橙皮與柑橘，但結構較鬆、厚度較弱。
若想保留中焙豆的明亮又避免薄，可把82°C抬到90°C左右；若想要堅果焦糖與巧克力感更厚實，悶蒸直接用92°C通常最穩。中焙要濃、要厚，先把悶蒸溫度、研磨粗細與粉床水路這三個關鍵顧好，TDS與杯感就會更接近你期待的方向。
The most valuable insight from this comparison is that a 0.01 difference in TDS can translate into a large difference in perceived body. With a higher bloom temperature, saturation becomes more complete and extraction more evenly distributed. Sweetness and brown-sugar notes (malt, nuts, cocoa) concentrate into a tighter structure. Even at nearly identical TDS, the cup feels denser and more cohesive. By contrast, low-temperature blooming with medium roasts often under-activates extraction, emphasizing orange peel and citrus notes while leaving the structure looser and the body weaker.
To preserve brightness without thinness in medium roasts, raise bloom temperature from 82°C to around 90°C. To emphasize nutty, caramel, and chocolate depth, blooming at 92°C is usually the most stable choice. If you want a medium roast to taste stronger and fuller, start by dialing in these three fundamentals: bloom temperature, grind size, and water flow paths in the coffee bed. Get those right, and both TDS and mouthfeel will move much closer to what you expect.
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