Bitter Press

Coffee, yo.

Contact Time vs. Extraction

There are five basic ways to affect extraction of coffee.

  1. Dose/Ratio — the more extended the coffee to water ratio, the more extraction you’re bound to get from the coffee.
  2. Grind — The finer the grind, the more surface area of coffee is exposed, the more extraction you’re bound to get from the coffee.
  3. Water Temperature — Certain desirable solids need higher water temperatures to dissolve, and water that’s too cool will prevent extraction to the desired degree.
  4. Contact Time — The longer the contact time between coffee and water, the more extraction you’re bound to get from the coffee.
  5. Agitation — Agitating coffee will promote quicker extraction, somewhat due to re-exposing surface area of coffee particles that have settled during the brew process.

These are obviously up for debate. And they might be a little off in their explanations for those who want absolute specificity or are prone to splitting hairs. 

What’s been bothering me lately, however, is the correlation between contact time and extraction. Monitoring contact time very specifically isn’t just a way to promote great consistency, it’s also a way to monitor extraction. 

This is especially true with brew devices like the Hario V60. Because of the large exit hole in the V60, the brew device requires a finer grind than most other pour-over brewers. Because of the finer grind, any shift in contact time larger than ten seconds will greatly affect extraction. Therefore, when brewing with the Hario V60 and using a continuous pour, one knows that a brew time of around 2:00-3:00 minutes is generally going to land within a good extraction for 300-600g of brew water. When brewing with 415g of water, however, I know that I need to land right at 2:15-2:25 in order to land at the desired extraction yield. 

Coffee brewing becomes fairly easy, then. Adjust grind until you reach desired contact time for selected brew ratio. But this is a very specific recipe. It requires exactly a 45 second bloom and 45 second pour speed, and exactly the right grind setting to achieve the right extraction. Things get more difficult when you look at not just other pour-over brew devices, but also different pour-over brew methods.

I don’t want to pretend to know a lot about coffee. I know a good bit, but I’m no scientific researcher. Most of my knowledge is pried and cobbled together from minds much more brilliant than my own. However, I do have two things going for me: obsession, and a quick learning curve. 

This style of thinking has geared me towards using a refractometer and MoJoToGo software to help monitor extraction rates in coffee. It’s a set of empirical data that can been used and tracked, and generally correlates with good tasting coffee. 

When using a refractometer to monitor extraction, one becomes very aware that when looking at extraction data, contact time isn’t as much of a set absolute. If looking directly at numbers, one can achieve higher extraction rates at shorter contact time by increasing agitation greatly and using much finer grinds. That doesn’t mean that coffee will taste very good, however. 

One thing I’ve found, on a personal preference level, that coffee when brewed through a pour-over brew device other than a Hario V60 tends to taste best with a coarser grind and a longer contact time. But not only do I generally prefer the taste of that coffee, I also appreciate the fact that with a coarser grind, I don’t have to nail my contact time to a perfect 10 seconds. Due to this concept of brewing, and my desired yield amounts, I’ve been brewing using 155 and 185 size Kalita Wave brewers. 

Here’s where it gets tricky. Most people will tell you that with a Kalita Wave brewer, you should aim for 3:00-3:30 contact time with the coffee. With this ballpark time, you’ll generally be within the ideal extraction rate. But when I attempted to start brewing with these two sizes, I found that I was having a hard time getting my brew time to extend to 3:00. My brews were consistently ending around 2:15-2:30, and no matter how slow I tried to pulse pour my brews, the coffee would always exit through the filter too quickly to even get close to 3:00. 

The coffee had been tasty, however, at 2:15-2:30. But I knew that those weren’t the desired contact times. So I began grinding finer, in order to prolong the brew time. And like you’d expect, I was able to extend the brew time longer. But I began consistently over extracting the coffee, and was drinking terribly astringent coffee every morning based on the fact that I liked the brew time. After bringing out a refractometer and monitoring my brewing again, I once more went coarser in grind and came to accept that my shorter brew times would be tastier than longer brew times that over extracted. 

In the meantime, my Hario V60 brews at work were still tasty and delicious at 2:15-2:25 and measuring desired TDS and extraction yield percentages. 

For months, my brewing and patience had been put to the test. I knew I was getting tasty coffee, but it wasn’t as tasty as I wanted it to be. But I had another lightbulb go off in my head. All this time, I had been trying to achieve a contact time that I normally only reserved for 24oz brews. Of course, the 3:00-3:30 advertised brew time for the Kalita Wave was also usually reserved for 24oz brews. My wife drinks tea in the morning, and when I brew coffee, I brew coffee just for myself. There’s no way I’m going to put down 24oz and feel good later on, especially when my job centers around coffee every day. So I had been targeting 12oz brews on the 155 size Kalita Wave, and 16oz brews on the 185 size Kalita Wave. 

Common sense would decree that larger amounts of coffee will of course take longer to brew for pour-over brewers. The physical act of pouring a larger amount of water will always take longer than smaller amounts of water. Maybe I had been chasing a dragon.

Still, there was something about the those longer extraction times with coarser grinds. 

And then I got to thinking this morning: if my coarser grind brews landing at 2:30 are giving me desired extraction yield and TDS rates, then if I ever wanted to mimic the 3:00-3:30 contact time, I’d have to adjust my grind even coarser to line up the contact time and grind size in order to avoid over extraction. 

Which, seemingly, was an impossible task. But I had learned a few things. My standard bloom time is 40 seconds. But I found that when brewing with Wave, the 40 second bloom time allowed the water to pass through the coffee much more quickly, much like pre-infusion with espresso. So I shortened the bloom to 30 seconds. Not only did the shorter bloom time keep me from over extracting, it also helped prolong the total contact time by somehow flattening the coffee bed further into the corners of the brewer and choking off the airflow and water flow through the holes in the bottom of the brewer.

Also, I found that the Kalita Wave filters at the top of the stack tend to be more squished, and don’t rest as tightly to the sides of the brewer as the ones from the bottom of the stack, which tend to be more flared out. 

Lastly, it seems that pouring in such a way that keeps the bed very flat during the first few pulses tends to choke the flow in a way that helps prolonged brew times. And with that in mind, today’s 34g coffee, 525g H20 brew clocked in at 3:15. It was dee-licious. 

The real issue here, however, is why? I know that some folks out there have put forth the idea of solubles on the edge of the coffee particle versus solubles in the center of the coffee particle creating different flavors. But with a finer grind, those internal solubles would be then surface solubles, and would extract just the same as a prolonged brew time with a coarser grind would eventually extract those center solubles. 

Or is it the process of slowly extracting from the outside in that creates more depth in flavor? Perhaps, like a time dissolving capsule, there’s a certain order to the way we want our extraction organized. 

Another major issue here is water quality. Water with a high hardness or high TDS of mineral content generally needs longer contact time to even get close to the desired extraction yield percentages. I know that when I was in LA brewing coffee, even with finely tailored filtration systems, the water clearly was extracting much differently than the water in Chicago. 

Which sucks. Because that means that any chance to really describe extraction times to people across the country is severely stunted by the varying degrees of water quality. Therefore, any time we give out contact times for brewing, we also need to publish the exact water make up numbers with it. And since grind size and and contact time aren’t perfectly married, maybe we need to publish the average micron size of grind particles for desired grind level. 

It’s more than just a rabbit hole. It’s a goddamned cave system. Which is, I guess, whatever. The goal is to be happy when you’ve achieved tasty coffee. A scale, a thermometer, and a timer will help you brew that tasty coffee consistently. Maybe that’s the extent that we can really examine extraction quality. 

What do I know? I have a degree in Fiction Writing. 

  1. bitterpress posted this