Can You Half Fill a Moka Pot Without Problems?

You’ve got a big moka pot but if you use it to its full capacity, it’s way too much caffeine for you. is it possible to fill the pot halfway and still make good coffee? Let’s find out.

It’s OK to half fill a moka pot with water and/or grounds without any danger or problems. However, this will change the taste and strength of the brew, even without changing the ratio of water to grounds. Best results are with 75-100% of capacity. For regular small brews a smaller pot is better.

Using half the amount of water will still make a moka pot work. However, there are some issues with the final result.

How a Moka Pot Works

To see why half-filling a stovetop espresso maker could possibly not give you the results you’d like, let’s start with how a moka pot works;

The water in the boiler forms steam. Steam takes up more volume than water so the pressure rises. That pressure can be relieved by pushing the water into the funnel through the coffee grounds. The hot water extracts the coffee while moving through the grounds and thus brewing coffee.

The coffee grounds provide resistance to the water flow. That creates extra pressure which helps the extraction of the coffee grounds.

While you can exactly measure the amount of coffee grounds and water, most people just fill the filter basket flush to the rim and the boiler up to just under the pressure valve. That way you use it as the manufacturer intended it. Filling the pot to just under the valve is considered best practice whether you exactly measure the amount of water or not.

Want to know how to actually use percolators to make good coffee? click here.

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A two or three-cup moka pot is good for a single person. Buying a smaller moka pot will yield better results than filling a moka pot less than full. You can find some great options below.

What Happens If You Half-Fill a Moka Pot?

So now we know how a moka pot works, let’s see what happens when you put less water and/or coffee in a pot.

Suggested: The Best Moka Pots To Buy

Does it work?

Sure it works. You can fill a moka pot halfway with water and/or grounds and it will work fine. It will work in the sense that water flows through the grounds and into the collector brewing coffee. There will be little coffee since coffee grounds hold on to 2 grams of water for every gram of dry coffee. Also, a moka pot doesn’t use every last bit of water from the boiler.

If I put 60 ml of water and 7 grams of coffee (half the capacity) in my 120 ml moka pot, I only get about 30 grams of coffee in my cup. The rest is lost along the way. However, if i use the full 120 ml, i get almost 100 in my cup. The loss stays about the same and at full capacity it’s even a bit more efficient.

 Moka pots have a reputation to possibly explode. This is very rare and using less water and grounds means the pressure and resistance are lower than what the pot is designed for so this is not an issue.

The differences will come in the taste and strength of the final brew. By using only 50% of the capacity, you get a pretty weak (and small) cup of coffee that’s quite acidic. That’s because of a few reasons;

Pressure and temperature

Putting less water in the pot means there is more room for the steam to expand into. So the pressure will build a little slower.

Because you use less water, you’ll also want to use less grounds. That means the bed of coffee is thinner in the basket. A thinner bed provides less resistance.

The boiling point of water is different under different pressures. At sea level it’s 100 degrees celcius. However, with higher pressure the boiling point rises. So; less resistance -> lower pressure -> lower water temperature.

Although this is likely going to make a small difference in the final brew, it can help a little with the common complaint about burnt tasting moka pot coffee.  Because the water is just a bit cooler, there is less chance to burn the grounds and therefore you get less of the burnt notes. Although because you’re getting a weaker cup overall, those notes are already less noticeable. You’ll get something that’s a lot less like espresso and a lot more like filter coffee.

With lower pressure you’ll also have less extraction which changes the taste.

Just something I though of while writing this up; you can use a paper filter (aeropress) in a moka pot. This increases the resistance a little which you could use to offset the lower resistance. However, you will also filter more fine grounds and oils out of the coffee changing the taste even more. I haven’t tried this yet myself so I’m not sure of the results.

Coffee expansion

Another part that changes is the expansion of the coffee grounds. Coffee absorbs water and in that process swells up. If you fill the basket flush to the top, it doesn’t have much room to expand because the filter lid is right there at the top. That means the grounds push against each other, filling all the tiny gaps between them.

This increases the resistance of the coffee bed. This resistance means a higher pressure is needed for the water to flow through it. This increases contact time and extraction.

Now if you half fill the basket, the grounds still have room to expand which means the coffee cake will have a much looser structure. This means the pot builds less pressure, the temperature is lower and the water moves faster. This leads to a lower extraction of the grounds. Taste wise this means less bitter but more sour. It also means a weaker cup even though you use the same ratio of grounds to water.

Extraction

In the end you will have a lower extraction even when using the same ratio. If this is a good thing depends on your taste and coffee you’re using. However, a moka pot is known for brewing strong, bitter coffee. by reducing the amounts, you won’t get anything like that.

You’ll end up with slightly less bitterness but more sourness. Because of the slightly lower temperatures you’ll also have less burnt notes.

Try it

The main problems are the taste and strength of the final result. Because of the lower extraction you can get a weak sour cup of coffee. You also lose some efficiency in how much liquid you get out of the pot. The losses are quite linear so by reducing the amount of water in the boiler, you’ll get a lot less liquid.

So, there isn’t anything inherently bad or dangerous about half filling a moka pot. It’s just that they’re not designed to work that way and you might just not like the resulting brew. Because there is no danger in trying except potentially brewing some bad coffee, you can always give it a try yourself.

By reducing both the water and grounds you’re going to get a weaker cup of coffee with a slightly changed taste. By reducing the water but not the grounds, you’ll get a strong cup but with a big change in taste.

If you’re happy with the coffee a moka pot brews but just want less of it, brewing a smaller batch is not the solution. If you want to adjust the taste and/or strength, go experiment.

What you prefer is really your personal taste, there is no right and wrong in tasting coffee, just preferences.

Of course the quality of the coffee and the beans you’re using also have an impact. If you’re using Robusta coffee, the lower extraction might be beneficial because you’re getting less bitterness. On the other hand, if you’re using a high quality Arabica, you want as much of the taste and different nuances as possible.

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How Low Can You Go?

If you’re going to give this a try, about 75% of the original capacity is as low as I would go.

When keeping the ratio the same, there will just be too little coffee in the filter to brew anything resembling coffee. At about 50% you will still brew coffee but it’ll be more like filter coffee in strength. Below 50% the bed of grounds gets so thin that not much is extracted anymore because there is no resistance. You’ll end up with a very weak cup.

If you just reduce the amount of water but leave the grounds the same, you will of course end up with a much stronger cup.  Although because there is less water, there is less extraction as well so you might end up with strong but sour coffee.

Also keep in mind that grounds absorb an amount of water (on average 2 grams of water per gram of dry grounds). This water stays in the grounds and doesn’t end up in your cup. So if you leave the amount of grounds the same but halve the amount of water, you actually get less than half the final amount.

Also, there is always a tiny bit of water left in the boiler you don’t use.

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Best solution

So you can decrease the amount of coffee you make in a larger moka pot but the taste is going to be different.

If you want to make sure your brew is perfect every time and don’t want to waste coffee, the best solution is to get a smaller moka pot. You might think that’s a waste of money but in the long run it will probably work out in your favor.

Because you’ll likely be using more coffee grounds than necessary to keep the strength up, you’ll be spending a few pennies more than necessary every day. Especially if you’re using a good coffee, it can add up over time. Let’s say you can use 10 grams less coffee in a smaller moka pot.

If you make one pot every day, that’s a saving of 3.65 kg (+-128oz) a year. At $0.50 an ounce, that’s $64 a year. That means with the savings over a year, you can easily buy a smaller moka pot, even from a good brand. If you get a cheap one you can probably buy 5 small pots for that amount of money.

Those are only the money savings. Wasting coffee isn’t all that good for the environment either since it has to be imported from South America or Africa.

Since a high quality moka pot can last for many years, it’s really a no brainer and much easier than struggling with using a moka pot for less coffee it was designed for.