Osmotic Flow for Light Roast Coffee

Osmotic Flow for Light Roast Coffee

In this article you will learn how to use Osmotic Flow for brewing light roast coffee. I’ve been researching and improving this technique for more than 2 years. And developed a simple, reliable approach with a clear explanation of how to adjust the flavor using it.

Around 99% of the coffee I consume is light roast (including super light from BOB coffee, roasted by Alexandru Niculae). And I was lucky to try to brew even competition level coffee using it.

What’s really important - it’s an organic way to brew. There is no need to memorize the amount of grams that you need to pour each time. Once mastered - you will be able to brew any dose of ground coffee from 8 g to 1000 g (I haven’t tried more than that).

Alternative to this - is my own, Hybrid Flow coffee brewing technique. Which requires less time spent holding the kettle. 

Brewing 1 kg of ground coffee (12.5 L of water) using Osmotic Flow

Contents

• What does it tastes like
• What is the Osmotic Flow
• Japanese way - the differences
• But water doesn’t contact with the coffee
• How to brew coffee - Osmotic Flow
• Osmotic Flow - Pouring technique
• How to adjust the flavor
• Extraction
• Video tutorial

What does it tastes like

It is usually somewhat cleaner and lighter than a regular “pour over recipe” where you pour the water over the coffee. It is also usually slightly “thinner” in flavor. For some coffee it could be great, for some - it could make

But mostly, it will just be a great tasting cup of coffee which will be very hard to distinguish from a regular pour over.

What is the Osmotic Flow

It's a coffee brewing method which originated from Japan. The concept is popularized by Cafec, the company which produces coffee filter paper. The main feature in it - water doesn't cover the coffee. Because we pour the water only in the center. That way it is easier to adjust the flavor and predict the outcome.

Japanese way - the differences

It is different because they mostly drink dark roasted coffee. And most certainly, a lower ratio. My approach is similar, but adapted to a filter coffee (light roast) with the ratio of 1:16. And uses a stricter structure based on time.

How Osmotic Flow works (boring stuff, skip it)

Water balances the concentration of liquid. That's why we don't need to pour over all of the coffee. Imagine it like this: a drop of ink is entering the glass with clean water. What will happen? It will distribute evenly, making all of the liquid more or less the same color.

Basically, coffee dissolves the chemical compounds which are stored in ground coffee. And while doing so, it shares these compounds to water molecules nearby.

In simple words, we have a highly concentrated liquid inside our coffee brewer after we added the first portion of water. And then, by pouring into the center - fresh water will balance the concentration (meaning reducing it). And at some point, our coffee (concentrated liquid) will leave the brewer.

Because we pour relatively slowly, there is enough time for the liquid in a coffee brewer to balance the concentration inside. And because we pour the water - there is a slight agitation going on, which helps to make the concentration more balanced.

And because we have this “continuous” reduction of the concentration of liquid inside - the extraction can be easily adjusted.

But water doesn’t contact with the coffee

I thought so too at first. But water actually “connects” everything during the bloom phase (when the first portion of water is added).

And when we add the rest of the water, coffee will actually float on it. So you don’t need to worry that the coffee could be “unevenly extracted” etc. It works great, if you adjust your grind size and water temperature.

How to brew coffee - Osmotic Flow

There will be three stages. And that’s the only thing that you actually need to remember in this method:

• Bloom
• Pulses
• Constant pour

First stage, Bloom

Here we just wetting the coffee. You don’t need to think about the exact amount of water. But you’ll need to practice it a little. The goal here, ideally, is to shape the “dome” from ground coffee. For this, usually it’s enough to use 2 or 3 times more water than the amount of coffee you’ve used.

If you’re brewing 15 g of coffee, it’s totally fine to use 30-45 g of water to wet the coffee. If you need more water than 60 g - the grind size is probably too coarse. But don’t think about the grams when pouring the water. The goal is to wet the coffee.

Second stage, Pulses

From 30 seconds to 1:30 - Pulses. It gives us an ability to have a higher extraction. Usually it is fixed by time, but you can play with it. The longer you will do this phase the higher extraction you can get.

I used to use pulses from 30 seconds to 60 seconds, but with time switched to 1:30 since it gives a better extraction. Because it helps to wet the coffee better (if it is still dry in some points). Or the flow is just too slow, especially with the big doses like 30 grams and more.

When it is 1:30 on your stopwatch - time to switch to a constant pour.

Third stage, Constant Pour

You just pour the water till reaching the final dose. The only number you need to memorize except for seconds (which is easy because they’re constant, just 30 and 1:30).

Osmotic Flow - Pouring technique

All of the pouring is gentle and slow. Very slow and gentle. Not higher than 6 grams per second in the first two stages and usually around 2 grams per second in the third stage.

And you need to pour pretty close to the coffee. Around 2-4 fingers above the coffee, preferably not higher.

Bloom

Make a relatively slow spiral from the center. Don’t pour near the filter in order to create a beautiful dome. Just cover the coffee with the “wave” when pouring around 1-2 cm near the filter.

Pulses

At this point you may have a great dome-shaped coffee. Or sagged in the center. Either is fine. Just make a small slow pour of water drawing a circle in the center (it's important, updated since 07/07/24) till you’ll have a foam almost overflowing from the center.

It will have a pumping motion (ground coffee). You add the water - it expands. You wait - it collapses. But don’t let it collapse. Pour the water again. And do that till 1:30.

The portions of water will be really small. Just be sure to not pour too much of the water or pour too early. Let the coffee “breathe”.

Constant pour

At around 1:30, when the coffee is ready, you can start constantly drawing a circle in the center. With the super slow flow rate (around 2-3 grams per second). Most of the kettles could start to switch to drips, that’s how thin the flow is.

The goal is to keep the dome “expanded” but preferably not overflowed by water. In some cases it could start to overflow - that’s still fine. Just be sure to pour slowly till reaching the desired amount of water.

After pouring the water, let it drain.

How to adjust the flavor

We mostly use grind size as an adjustment. And a water temperature.

As for the water - start from 90°C. Usually it’s enough and not too much. If coffee lacks acidity and complexity - increase the temperature (it will become brighter). But usually, when you increase the water temperature, it’s better to decrease the grind size a little as well. It’s done to compensate for a higher flow rate of water.

Usually, the range is around 88-92°C. If you go higher - bad aftertaste could appear.

For slow coffee filters, I would start from 92°C since we need to have a good “agitation” inside. And the higher the temperature the easier for water to flow through the coffee.

For degassed coffee it is usually better to increase the water temperature as well. For the same reason - having a better flow. Because such coffee will be compressed and it will be harder for the water to go through.

If there is a “roasty aftertaste” or it’s just unpleasant and drying - better to decrease the water temperature.

If coffee is “muted”, “mellow” and “boring” - increase it.

As for the grind size - start from a slightly smaller than for regular pour over. Like sugar to the touch and smaller.

For a 15 g dose - I use 2.8 - 3.0 on Kinu m47 (2 rotations + 8 numbers or 3 rotations). Or around 17-20 clicks on Comandante c40.

Pay attention to the body. If coffee is watery - decrease the grind size. If coffee is drying - decrease the grind size. And if water flows too fast through the coffee so that you are forced to pour faster - decrease the grind size.

It should have a lingering, pleasant aftertaste if there is enough body.

Alternatively, you can increase the dose of coffee. Since there will be a pretty coarse grind size which is easier to brew better.

What if I change the dose of coffee that I'm brewing?

In case of increasing the dose from 10 to 20 grams - increase the grind size. 

From 20 to 30 grams dose - you'll need to decrease the grind size. Why? Because you have more water pressure and it will flow even faster. So we slowing it down with the resistance of coffee itself, not just paper filter.

If you want to decrease ratio (from 1:16 to 1:12)

In such case, increase the grind size. Because you will have a higher concentration of liquid with 1:12 ratio, in order to have a balanced taste, extraction should be lower.

Extraction

We mostly regulate the extraction by adjusting the grind size. But after reaching some point - you can play with the pulses stage. I found that for Comandante it works better with a 0:30-1:00 pulses phase. And if you want a higher extraction - you can go as high as 2 minutes or even skip the constant pour and use the pulses till the end.

Total brewing time for 15 g dose (250 g of water) is usually 2:40 - 3:00. For 30 g dose - 3:00 - 3:30.

That’s the most important information that you need to know about this method. If it helped - you can support me on Patreon ;)

Video tutorial

In some videos I use pouring in the center. It works, but it's way better to use circle pours instead.

Detailed video tutorial