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Thesis
Section 5 is not really about “其火用炭次用劲薪其炭曾经燔炙为膻腻所及及膏木”; it is about how Lu Yu turns tea from a local product into an object of argument.
Text
“For the fire, charcoal is best, and sturdy firewood next. Charcoal that has been used for roasting, stained with fat and rankness, as well as resinous wood and rotten utensils, must not be used.”
Context
劲薪：耐烧的柴。燔炙（fán zhì）：烧烤过。膻腻：腥膻油腻。膏木：有油脂的松柏等木。败器：腐朽的器物。
Evidence
- Collation: 各本一致。吴觉农注：此句讲燃料选择，“膏木”"败器"皆能产生异味与烟气，破坏茶香。
- Existing readings: 吴觉农评此句为"燃料学"：炭火无烟无味最宜煮茶，沾油之炭与松柏膏木皆会串味——陆羽对火候细节的讲究，尽显茶道"洁净"之美。
Analysis
Formally, the section gives a judgment, adds material detail, then returns to human practice. 劲薪：耐烧的柴。燔炙（fán zhì）：烧烤过。膻腻：腥膻油腻。膏木：有油脂的松柏等木。败器：腐朽的器物。 That is why the Classic of Tea reads as an argued book rather than a miscellany.
Conclusion
The section does not give a universal rule. It demonstrates a method: read the text, the annotation and the Tang context together before making a modern claim.
Source: The Classic of Tea, Chapter IV · The Vessels, section 5; the original is in the public domain.
Get the character right before the taste.