mobeets Senior Member Joined: 28 Jun 2012 Posts: 3 Location: Melbourne, Victoria Expertise: I love coffee
Posted Thu Jun 28, 2012, 11:11pm Subject: Chemex variables...and confusion
I was thinking last night about how a pour-over coffee forces a relation between coffee strength and extraction level that doesn't necessarily exist when making, say, a french press.
This is because a filter will let a fixed amount of water pass through the coffee in the brew time necessary to reach your desired extraction.
A filter lets water through at a certain rate that is dependent (I'm assuming) on grind size and the amount of coffee you put in the filter. Each day I make a coffee I'd like to be drinking the same amount of caffeine, so all that leaves me room to adjust is the grind size.
Assume now though that I want to make coffee for me and a friend. By doubling the amount of coffee, I'm decreasing the amount of water that will get through the coffee in my fixed brew time. So I need to increase the grind size to compensate, correct?
The reason I'm asking is that I've read other people suggesting that you both overdose and underextract when making a Chemex coffee. Why would they not just increase their grind size instead of wasting coffee and underextracting?
Yes, that was very helpful! I have some clarifying points about my initial question...
First off, I should have said that I'm looking for a constant volume of coffee at the same strength--not the same amount of caffeine.
My problem is that I've noticed my brew water is taking WAY too long to get through the grounds, i.e. the percolation rate is way too low and so the coffee isn't tasting too good once I get all the water through it. It tastes weak, actually, though I'm using a 17:1 brew ratio.
Based on the reasoning I described in my first post, it seems like all I need to do is increase my grind size as this will increase the percolation rate and get the same amount of water through the grounds in nearer the ideal contact time. But I've read other people saying that when they make a Chemex they prefer to overdose and underextract?
My question is, what are the differences between increasing grind size vs. the overdose/underextract approach? And why would underextracting possibly be a good idea?
And thanks for the equations, that seems like a good thing to measure. I'm curious to see what a Chemex's absorption is, but I'll have to wait until the weekend...
I'd definitely agree that I'm getting a "contact brew," because the water doesn't drain at all near the end. I'll loosen up the grind and see if that helps. Plus, my water temperature drops quickly (when making coffee at work) because I've got water coming out of one of those "insta-hot" faucets--so I've got nowhere insulated to keep my hot water! Agh.
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