COFFEE GRIND ANALYSIS SIEVES-There are two simple sieve analysis tests (Often referred to as ROTAP ANALYSIS).
Rotap refers to one of the original pieces of equipment manufactured specifically to simulate the effects of shaking a sieve by hand, ie...rotating / tapping, the earliest collaborated standard. Although agitating a sieve by hand is difficult at best, (Hold the sieve, with pan and cover attached, in one hand, at an angle of about 20 degrees from the horizontal. Move the sieve up and down, in the plane of inclination at the rate of about 150 times per minute, and strike the sieve against the palm of a hand at the top of each stroke....SOURCE ASTM MANUAL ON TEST SIEVING METHODS) it was viewed as a starting point. Because of this, many, if not most of the initial studies on coffee grind size, were conducted using a TYLER ROTAP Machine, ie... ROTAP ANALYSIS)
Fortunately, newer and more user friendly technologies (An actual ROTAP Shaker, requires a separate room or sound proof enclosure) came about to perform this task, but many industries still get caught up in antiquated nomenclature. Tyler Rotap Sieve designations, are often mistaken for the current official ASTM Sieve Designations. Use this handy conversion chart, and always make sure you include the millimeter equivalent, when discussing laboratory sieve tests.
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FINISHED QUALITY STACKING HAND SCREENS WITH
EXTRA DURABLE SIZE LABELS
LIDS AND RECEIVERS
ROASTERS
TEST 1- In order to verify that a coffee grinder is operating to specification, take a representative sample
of ground coffee, from a freshly calibrated grinder with new burrs, and run the sample through the sieve stack. Because you are just establishing a benchmark, it isn't really necessary to reach the endpoint here, but whatever time frame you use, it must be long enough to show a difference if the grinder is experiencing problems, and short enough to let you know in time to do something about it. We can't really recommend a time frame, because it depends on the performance characteristics of the sieve shaker you have. Use this
sieve shaker amplitude gauge, to catalogue / verify your sieve shakers performance.
TEST 2- If you took one roasted coffee bean and split it in to two pieces, and soaked it in hot water
for 2 minutes, and then took another bean, and ground it in to 1,000 pieces, and performed the same test, you would find a dramatic difference in the end result. That is because the smaller the grind size, the more exposed surface area, the less contact time is required to achieve the desired extraction.
So for each different type of grind, whether it's Espresso, or Automatic Drip, there are optimal
particle size distribution parameters, and water contact times to achieve desired extraction rates.
Luckily someone took the time to painstakingly document the effects of this phenomenon, and provide at least a good starting point. The below chart has been revised with ASTM Sieve Designations.
NOTE: DUE TO THE MORE ANALYTICAL NATURE OF THIS TEST, IT IS IMPORTANT TO REACH THE SIEVING ENDPOINT, WHICH IS DEFINED AS THE POINT WHERE THE AMOUNT OF SAMPLE RETAINED ON ANY ONE SIEVE CHANGES LESS THAN 1% (.1% FOR AUDITS) WITH ONE ADDITIONAL MINUTE OF SIEVING.
WITH THE SIX PRIMARY SIEVES USED IN THE COFFEE INDUSTRY FOR GRIND SIEVING.
THIS SMALL (10 INCH FOOTPRINT) VIBRATORY SIEVE SHAKER WORKS WELL WITH COFFEE.
LEFT: STAINLESS STEEL COFFEE BEAN GRADING SIEVES
FOR SIEVE SHAKER.
A COFFEE LABORATORY INNOVATION!
Because it is not always practical, or affordable to have a sieve shaker, hand screens are often used for the task of grading coffee bean size. Although the numbers used to designate bean grading sieves, look similar to the numbers used to designate grind analysis sieves, ie...#10,#12 etc...., they actually refer to perforated round holes in 64th " increments. So, a #10 bean grading sieve is actually 10/64th of an inch.
