Apr 8, 2009|
Question

From Roastmaster Tom

Dear Dr. Brew,
I am in the retail coffee industry. I have owned your CDBC brewing systems as well as the ICB system that I have in my shop currently. I have searched for information regarding pre-infusion and pulse brewing parameters without much success: (SCAA.org, Ted Lingle's book on coffee brewing, all over the Internet, etc).


I assume that pre-infusion is to prepare the grounds for extraction. How long should the grounds be wet before brewing takes place? How wet should the grounds be (ie, should I see drips of coffee coming from the brew basket, a stream, or no evidence of water at this point? How long should the grounds remain wet before brewing takes place? ...


(more of Tom's letter in the next post)

Thank you
Tom Walsh
roaster/owner
Cambria Coffee Roasting Co.

Answer (Part I...Preinfusion)


Dear Tom,


Here's how pre-infusion fits into the brewing process.
Pre-infusion, or pre-wet as some refer to it, saturates the coffee grounds and begins the brewing process. This allows the ground particles to absorb water and swell in size and release carbon dioxide, opening the paths for the remaining water to more easily penetrate and extract the coffee (soluble material). I have found this brew method to be effective with extremely fresh coffee that still contains most of the Carbon Dioxide in the bean from roasting. This also helps with decaffeinated coffee that does not expand as far as its regular counterpart during the wetting proces

To explain pre-infusion, I often use the analogy of a pre-soak cycle in laundry. The purpose is the same -- to expand the material from which we want to extract the soluble. Pre-infusion as a cycle consists of an initial ON time, a pause, and the remainder of the brew cycle. Of course, there are variations depending upon manufacturer. The initial ON period should provide enough volume to saturate the ground coffee.

Ground coffee absorbs approximately two times its weight in volume -- for example, a brew formula of 8 ounces of ground coffee to 128 ounces of water. The initial ON time needs to be sufficient to deliver 16 ounces of water at a minimum to saturate the ground coffee. I prefer to deliver between 15 - 20% of the brew volume for the Initial ON time. This seems to get the grinds saturated and in float.


The pause or OFF time can be for as few as 5 seconds or as long as 4 minutes. I personally do not allow the OFF time duration to allow flow to stop from the funnel outlet. This has something to do with grind size; I have found the finer the grind, the shorter the OFF time. With some fine-ground coffees, if the wet bed of grounds is allowed to collapse, the particles stick together and the water flow for much of the remainder of the cycle flows around the coffee rather than through it.


To convert initial ON time to volume for your brewer follow this example:
Determine spray head flow rate in ounces per minute. 32 opm/60 sec = .53 opsec 15% of 128 ounces = 19.2/ .53 ops = 36 seconds of initial ON time


To find the right preinfusion -- experiment, experiment!

Happy Brewing,
Dr. Brew

(in the next post I will answer Tom's questions about pulse brew)

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