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IMMERSION BREWS & MEASURING EXTRACTION


Vince Fedele of VST, the coffee industry leader in brewing measurement devices, amongst other things, delivered a very notable talk at the Nordic Barista Cup last weekend. Go to the NBC site to see a video of his talk. The key subject of twitterdom and indeed the talk of NBC attendees was the apparently heretofore incorrect charting of immersion brews on traditional brewing charts. I thought I would blog a quick and dirty synopsis of Vince’s findings, as I interpret them: - when one uses immersion, steep or infusion brews, the total brew water volume extracts coffee solids. - when the brew is ‘complete’ to one’s taste, the beverage is filtered through whatever medium the brew method presents (paper, steel mesh, etc). - the coffee grinds absorb approx twice their dry weight of the liquid, IN THIS CASE BEING THE BEVERAGE. - thus, the grinds retain some of the extracted coffee which was dissolved in the beverage. In numbers: - using 60g of dry coffee and 1 litre of water in an immersion brew method. - assume 1.5% strength of final beverage for calculation purposes. - assume 2g of liquid absorbed by 1g of dry coffee. - thus, 60g of dry coffee absorbs 120g of brewed coffee. - thus, 1.8g of this dry coffee is dissolved in the 120g of the retained brew(120g x 1.5%) and is NOT in the final beverage. - this 1.8g of dissolved coffee must therefore be excluded from the final beverage. - this 1.8g as a percentage of the original 60g is 3%. - thus, a brew calculated as 17% extraction using current norms is indicating 17% of the original dry coffee has been dissolved in the beverage. - if 3% of the original 60g is retained in the grinds, the actual extraction is 20%. Thankfully, Vince’s wonderful new software does all the calculations for you. Hope it helps.

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