Brew Basics: Where'd My Coffee Go?

After a while of carefully measuring my coffee I noticed that I was not getting the same volume of coffee out of the grinds as water that I was pouring in. Where was this extra water going and how much was disappearing? Was there somebody or something in a different dimension that was enjoying that last little bit of coffee that should have ended up in my cup?

Obviously I know it wasn't getting beamed up by a sleep deprived, caffiene hungry alien, but I needed to get to the bottom of this.

When you make coffee you want to know how much you're going to get. You want to make sure it's going to fill that cup right to the top! If you have a 10oz cup, you don't want 8oz of coffee...do you? Thus began my attempt to further measure my coffee brewing. I started measuring my net brewed coffee (physical coffee in my cup). I also subtracted the net from the total amount of water that I poured into the coffee bed, to give me the volume of water that didn't make it through. I would usually measure this by weight/volume and then convert it into a percentage. When I calculated the percentages, I would find that the number would fluctuate quite a bit at times. Most often I found that the grinds held an average of 12% of the water poured in. This percentage varied other times anywhere between 9% and 15% depending on the coffee origin and grind size. This number is also going to fluctuate depending on how long you let your dripper sit on your server.


Later after more reading, I found out that this liquid being absorbed by the grounds is called the "interstital liquid" and it's a variable commonly measured in the coffee community, especially in cafes to perform cost profit analysis. I also learned that the interstitial liquid is expected to retain twice the amount of water as coffee used when brewing. For example; if you used 20g of coffee to brew, it's calculated that about 40mL of water will not end up coming out of your brew. Wow, was I ever relieved to learn that I was not crazy for measuring this...

So now you might be thinking that you're getting gypped that your brewer isn't giving you all that it could. Maybe you're thinking that you should squeeze out the remaining water from in your filter. I do not recommend this. Squeezing the last little bit out of your filter isn't going to benefit your cup in any way. "More coffee means more caffeine, right?" Nope. "More coffee means more tasty goodness, right?" Not in this case. It's argued that the interstitial liquid has a negligible amount of strength to it. At this point in the brew process, your coffee has likely already given you everything positive that it has to give! This is not to say that it doesn't hold negative flavours. By squeezing out the rest of your coffee, you are likely to introduce unwanted bitter, dull, chalky flavors to your cup.

Here's the solution to your 12% shortage. If you want to fill your favorite Saturday morning mug to the top, just increase the quantity of coffee that you are brewing. If you were coming up short with a 20g dose, try using a 23g dose!


I don't recommend just pouring more water through your original 20g of coffee because this could potentially create a whole new issue for you and your quest to crafting the perfect cup. I touch on that a bit in Brew Basics: drip/pour-over.


I hope this has provided you a bit more clarity on where that last bit of coffee had disappeared to.

Remember to always strive to brew coffee better!


*how do we feel about GIFs? yay or nay?