Presentation on theme: "The Effect of Home Grinding on Brewed Coffee Properties Chris Murray and Thamara Laredo Lakehead University Thursday, June 19, 2014 Chris Murray and Thamara."— Presentation transcript:
The Effect of Home Grinding on Brewed Coffee Properties Chris Murray and Thamara Laredo Lakehead University Thursday, June 19, 2014 Chris Murray and Thamara Laredo Lakehead University Thursday, June 19, 2014
Motivation Do you know this man? Or someone else like him? Someone who grinds the coffee beans for a ridiculous amount of time, hoping to squeeze every Joule of caffeine out of it? This study is for Ludo Dian and those of us like him. Mr. Ludo Dian
Previous work Effects of roasting – Budryn et al. 2009; Crozier et al. 2012; Hecimovic et al. 2011 Effects of bean type – Crozier et al. 2012; Belay et al. 2008; Fox et al. 2013; Tello et al. 2011 Effects of in-store and at-home grinding – Bell et al. 1996 But not enough! How much can you increase the caffeine by grinding?
Procedure 37.5 g of beans, ground with blade-type grinder, Why? Timed relay: 0 to 84 seconds Measure: – Particle Size Distribution – Tablespoon mass – Percolation time – Mass loss on brewing – Water loss on brewing – Caffeine content of coffee
Results (Part 1) With grinding up to 42 seconds – Average particle size is reduced from ~ 6 mm to under 200 microns – Distribution narrows with grinding – Small increase in ground coffee density Caffeine* can at least double with enough grinding *or at least everything absent in decaf No further change with more grinding > 42 s
But why? The result of direct importance is qualitatively obvious but quantitatively surprising It is of interest to understand what is causing the increase in caffeine with grinding Several other factors change with grinding: Mass loss upon brewing The time for percolation to complete The loss of water (or retention by grounds)
Which might affect caffeine? Are finer particles providing greater surface area for exchange of caffeine with water? Are grounds coming through the filter contributing to the caffeine as they sit in the coffee? Is more time spent percolating increasing caffeine? Is the water lost increasing the caffeine concentration by reducing the amount of water?
Test #1: With all other conditions held the same: Allow one batch of coffee to sit for less than five minutes before extraction, and another to sit for over 20 hours If grounds coming through the filter contribute to caffeine, then more time in the coffee should increase caffeine Result: no effect
Test #2: With all other conditions held the same: Allow one batch to brew normally and for another batch, by restricting the opening on the percolator prolong the percolation by 20% Small increase, but so is observed increase with grinding If the “residence time” in the grounds influences caffeine, we should see an increase Result: no effect
Conclusions Grounds passing the filter and residence time in the percolator have neglible effect on caffeine content Increased caffiene with grinding is likely most strongly influenced by increased available surface area for contact with water Consistent with observation that finer grounds retain more water
Summary Grinding for times beyond manufacturer recommendation can double the caffeine content of brewed coffee Beyond 42 seconds, further grinding had little effect Caffeine is not strongly affected by grounds that pass through the filter or percolation time Water retention increase consistent with increased contact surface resulting from finer particles
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