Coffee Bean Grading has to do with a number of characteristics, one of the most important being size. Not only are larger beans generally more desirable, but bean size , density, and moisture are all factors that must be taken in to consideration when establishing roast profiles
COFFEE BEAN SIZE GRADING SIEVES
Bean Sizing Sieves are used to separate the coffee beans by 64th of an inch increments, starting with 8/64ths, all the way up to 20/64ths of an inch. Different countries use somewhat different size classifications,
and there are different methods available for green coffee grading. The SCAA METHOD and the BRAZILLIAN / NEW YORK Method are both in practice today. (SEE FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS) for more information.
Although the millimeter equivelants on this popular chart, aren't exact, it fortunately doesn't have any real impact on the size analysis. The New York Grading Chart
has exact conversions, but both result in the
same distribution because the tolerences are too small to impact 64th inch seperations.
"Some say there is an art to great coffee. I don't care how artistic you are; there are too many factors in play. You need the technology."
Forbes Magazine, Bob Stiller Green Mountain Coffee
Sieve Shakers are used to agitate the nest of sieves so that the grinds or beans fall through for sizing purposes.This miniature 3" Sieve Shaker comes in a handy carrying case, for transport to field locations, where grind or bean analysis can be done on site.
Grind analysis is a key component to producing a.good cup of coffee. Coffee companies spend tens of thousands of dollars on laser systems or less expensive sieving equipment to help analyze particle size and distribution, but why?
Grind distribution affects the extraction rate. Although there is no "correct distribution" this chart shows popular grind distributions for different grinds.
When performing a grind analysis, it is important to use USA Standard, ISO / ASTM Mesh Designations, especially when dealing internationally. Some companies as well as countries have their own mesh designations, but ASTM (American Society for Testing Materials) introduced standardized designations in the early 1900's to help eliminate confusion.
#12 1.70mm
#16 1.18mm
#20 850 microns
#30 600 microns
#40 425 microns
#50 300 microns
Even size distribution assures consistent extraction rate. Target extractions of dissolved solids should be 18% to 22%
The smaller the coffee particle, the less contact time required to achieve optimal extraction. Water contact times vary between 1 to 4 minutes.Under extraction makes for a weak coffee. Over extraction releases undesireable chemical compunds that result in negative taste quailites like bitterness.
Regular grind size analysis provides important information on grinder settings and grinder maintenance requirements.
NOTE: Coffee grind analysis is often incorrectly referred to, as a RoTap Analysis.
A RoTap Machine is a mechanical hand simulation sieve shaker that was introduced years ago, and used in many preliminary studies. Newer technologies have brought about much more ,"friendly" sieve shakers, that do not require sound enclosures or separate rooms.
