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Variables in Immersion Brewing

IM 1.03 Breaking the Crust

Most immersion brew methods require baristas to break a crust of coffee at some point during the brewing process. When cupping, the convention established by the Specialty Coffee Association is to break the crust 3–5 minutes after the pour. Our research into this process suggests that the highest extraction yields are achieved when the crust is broken after 5 minutes. 

Experiments by Barista Hustle into the effect of the crust of coffee on immersion brewing have revealed some unexpected results. You might expect that stirring the crust after 1 minute, which ensures all the grinds are fully submerged, would increase extraction — surprisingly, it doesn’t. Nor does leaving coffee sitting for as long as possible with the crust intact lead to maximal extraction. The fact is, there’s a sweet spot after 5 minutes, which the experiment demonstrates.