You haven't generated enough of those melanoidins and those kind of compounds that give coffee its colour.

你还没有产生足够的黑素和那些让咖啡有的化合物。

And don't forget, the colour of coffee itself comes from what are called melanoidins, like brown byproducts of roasting.

别忘了，咖啡的来种叫做黑素的物质，就像烘焙时产生的棕副产品。

There's been a lot of research done on this and broadly speaking, they think the active surfactants in espresso are probably things like melanoidins, a protein derived, roasting byproducts.

这方面有很多研究，般来说，他们认为浓缩咖啡中的活性表面活性剂可能是黑素，种蛋白质衍生的烘焙副产品。