Transfer Function for Cold Drip Coffee

Coffee preparation techniques besides espresso like pourover.
Tim M

#1: Post by Tim M »


I should start out by saying I'm a novice in the coffee world. I know little of the language and even less of the science.
I've been spending some energy thinking about all the variables involved in cold drip brewing with the ultimate goal of deriving a transfer function for the control of a medium scale cold drip brewing machine.

For those of you who don't know about control theory or transfer functions, it's math which describes inputs and outputs in terms of the variables.
I'm personally pretty useless at the math, I don't think about things like that, but I can't stop thinking about the system as a whole and I really would like to nut out the math before I start making a design for a machine. I'm also keen on the mechanical side of the machine, but the how and why of a design should really be driven by the needs of the system. Uniformity, repeatability and controllability are the goal but what needs to be uniform, repeated and controlled and how can you work through it systematically to tune a machine for each roast?

Obviously the desired output is delicious coffee which is very, very subjective... there's a lot of variables to tweak and there's going to be a lot of smaller little looping systems which all affect each other and tying that all together to make a scientific method which can be worked through quickly and efficiently to set a machine up to create the desired output is what I'm ultimately after. Or just something to think about.

The variables I can think of are, and some of these are functions of the others:

Total Water Mass
Water Flow Rate (in/out)
Puck Diameter
Puck Height
Puck Mass
Puck Density
Grind Size and Distribution

What can we measure from the output that's not subjective? Here's what I can think of:

Total Dissolved Solids

How do these relate to extraction, or the right amount of extraction? Tasting and comparing to metrics? Creating these metrics in relation to taste and extraction? What is the right amount of extraction scientifically? How can this be tied to the subjective outcomes?

If anyone wants to chew on any part of this post please chime in. I want to expand all the inputs and outputs, variables and metrics as far as possible. Pick on something/anything and explain away, add to the lists, talk about how one variable effects another, use math or emotion... any language is appreciated because I'm so green at this I don't really know what to care about yet let alone how to feel about it or control it.

Thanks for your time.



Tim M (original poster)

#2: Post by Tim M (original poster) »

So, today I found this paper: ... 19)30410-2

Here's an Hoffman video about the paper (this is how I found it):

I'm still absorbing it bit by bit, in-between meetings, it's definitely fueled my interest in this subject though. I note there's been no traction on this thread, maybe I'm dreaming a bit to hard but I'm still keen for any information about variables and effects that you may think of.