The Effect of Home Grinding

on Brewed Coffee

Properties Chris Murray andThamara Laredo

Lakehead UniversityThursday, 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

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

Thank you!

For more information, please email:cmurray1@lakeheadu.ca

ReferencesBELAY, A., TURE, K., REDI, M., and ASFAW, A. 2008. Measurement of caffeine in coffee beans with UV/vis spectrometer. Food Chem. 108, 310–315. BELL, L., WETZEL, C., and GRAND, A. 1996. Caffeine content in coffee as influenced by grinding and brewing techniques. Food Res. Int. 29 (8), 185-189. BUDRYN, G., NEBESNY, E., PODSDDEK, A., ÔYRELEWICZ, D., MATERSKA, M., JANKOWSKI, S., and JANDA, B. 2009. Effect of different extraction methods on the recovery of chlorogenic acids, caffeine and Maillard reaction products in coffee beans. Eur. Food Res. Technol. 228, 913–922. CROZIER, T., STALMACH, A., LEAN, M., and CROZIER, A. 2012. Espresso coffees, caffeine and chlorogenic acid intake: potential health Implications. Food Funct. 3, 30. FOX, G., WU, A., LIANG, Y., and FORCE, L. 2013. Variation in caffeine concentration in single coffee beans. J. Agric. Food Chem. 61, 10772–10778. HECKMAN, M., WEIL, J., and GONZALEZ DE MEJIA, E. 2010. Caffeine (1, 3, 7-trimethylxanthine) in Foods: A Comprehensive Review on Consumption, Functionality, Safety, and Regulatory Matters. J. Food Sci. 75, 77-87.

TELLO, J, VIGUERA, M., and CALVO, L. 2011. Extraction of caffeine from Robusta coffee (Coffea canephora var. Robusta) husks using supercritical carbon dioxide. J. Supercrit. Fluid. 59, 53– 60.