Brewing Large Batches of Coffee With the Chemex

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Christmas is only a week away. Work parties and family gatherings are imminent and if you are excited about coffee, there is a good chance that you are contemplating taking your manual brewing show on the road.

Sharing your love of coffee with the world can pose some interesting questions that don’t come up in every day manual brewing scenarios. One of the topics I see floating around a bit (especially this time of year) is how to brew large batches of coffee via the pour-over method.

The Chemex is my large batch brewer of choice. It comes in a variety of sizes with capacities from 350 mL or to about 1400 mL (1850 mL if you have the Thirteen Cup Chemex).

Simply owning a brewing device that has the capacity to brew large batches of coffee isn’t enough. Brewing a big batch of coffee has different challenges and nuances that should be addressed. It is not the same as brewing a small cup of coffee for yourself.

Over the past month and a half, I have been experimenting with brewing large batches of coffee on the Chemex and here’s what I learned.

What defines a big batch of coffee

For the purpose of this article, I consider anything above a 500 mL batch (two servings) of coffee to be a large batch. For recipes up to and including the 500 mL size, I really don’t make any changes in my techniques or grind size (although I must admit that I typically brew either 375mL or 500mL batches in my Chemex so there is very little variation to consider).

My go-to big batch recipe, is simply doubling my 500 ml recipe and adjusting the grind size. My brewing time for this is typically around 5-6 minutes.

For increments of a few hundred milliliters below 500, I find the slight variations of extraction within an acceptable range. If I were brewing for anything other than personal enjoyment (competition or commercially) perhaps I would work a little harder at dialing in specific recipes with incremental grind adjustments and timing metrics.

For anything larger than 500mL, things have a greater potential to go a little haywire. It is harder to brew a big batch with consistency and things can rapidly get beyond your control.

Three problems with brewing large batches of coffee

There are three major factors that contribute to the increased difficulty level of brewing a large batch of coffee.

1. The average person doesn’t get much practice- Manual brewing is typically done for single or double servings of coffee. It is a rarity to have the occasion to brew 1000 mL or more. If a situation presents itself, most people will reach for their automatic drip coffeemaker.
2. Errors or equipment deficiencies are compounded- When brewing large batch sizes, the impact of small mistakes can start to compound. Something that didn’t seem like that big of a deal over a 250 mL brew, becomes a huge deal when you take that batch size and multiply it by 4 or 5. Equipment deficiencies (mostly grinder) can really start to be a problem. An inconsistent grind with lots of fines can choke your big batch and make brew times very inconsistent.
3. When brewing a large batch, the pressure is on- In addition to the two issues listed above is the fact that when you are brewing a large batch it is often for co-workers, family or guests.  This means when you are brewing a large batch of coffee, the stakes are higher and you feel the pressure to nail it (if this is you, make sure you read the last paragraph).

My Experience (and advice on brewing large batches of coffee)

Over the past month or two, I’ve been able to practice brewing large batches on my Chemex. Among other things, I have been bringing my Chemex to work once a week to brew for my colleagues. This means each week I am able to brew two or three 1000 mL plus batches of coffee.

I get the opportunity to taste the results each time I brew, compare and work on improving my technique. The practice and the feedback have been good.

A Note on Consistency- Consistency is a lot harder to obtain with large batch brewing

As hard as I have tried to keep everything the same, I am still not able to consistently nail the brew every time. Every once in awhile, I will have one that chokes and goes several minutes longer than planned. I attribute this to a variety of factors but I think the major one is my grinder.

Even though I love my Virtuoso, it still produces some fines (especially at the coarser grind settings). The larger the batch size the more fines (more coffee used equals more coffee ground). Since the same filter is used for a large batch, there can be 3-5 times more fines than your usual recipe size. This can contribute heavily to filter clogging.

Pouring technique, filter positioning and water temperature can also make a big difference.

The Chemex filter can have a tendency to collapse over the pour spout (even with the three-ply side placed correctly) when brewing a large batch. Pay attention to this detail. If air is not allowed to escape from the bottom of the brewer, your draw down time will increase.

I have found that keeping your brewing slurry away from the Chemex brim should help the filter from collapsing over the sprout.

Tips for success

Here are a few things that can help you dial-in your large batch brewing technique:

Step one: Start by aiming for a time

This is one of the best pieces of advice I can give on the subject. If you really want to get better at brewing large batches, you are going to have to practice a bit. There is no magic grind setting (settings vary even between the same grinders), formula or timing metric.

The Chemex website says to expect brew times of 6-7 minutes when brewing a 10-cup batch and that has been my experience. Grind your coffee coarse enough that your brew is dripping out around the seven minute mark.

Another big batch recipe I’ve been using is 75 grams of coffee, 1240 grams of water and a 7:30 brew time. For a batch this size, I recommend grinding right in the middle between your normal Chemex particle size and French press.

Step two: Adjust for taste

How the coffee tastes is the most important part of the process but it is hard to find that sweet spot if you don’t start out in the ballpark. The brewing time gives you an idea of where your ideal extraction should be (an extremely short brew time or extremely long brew time indicates you will probably need to adjust your grind accordingly before really digging into how it tastes). The tasting part works in tandem with brewing time to find your sweet spot.

Quick review: If your coffee is taking too long to brew, it should be ground coarser. If your coffee is brewing too fast, grind it a little finer.

Here are some basic adjustments you can make based on how the coffee tastes (these adjustments work for regular batch sizes as well as big batch sizes):

1. If it is sour or thin– If the brew tastes sour there is a good chance it is under-extracted. If you have the timing where you want it, trying stirring the slurry a few times during the brewing cycle. If your time is off or you don’t want to stir, try adjusting the grind to a finer setting.
2. If it is bitter or harsh– If the brew tastes bitter there is a good chance it is over-extracted. To fix this you can try adjusting the grind setting to coarser. Avoid excessive agitation of the coffee bed (like stirring) and try adding water at an increased rate (to attempt to decrease brewing time).

Other helpful tips

Here are a few other helpful things to keep in mind:

• Don’t rush- Take your time when you are brewing. If you have a recipe and technique, don’t let the pressure of people watching or a sea of empty mugs push you into hurrying.
• Take notes- If you are working on your large batch brewing techniques, don’t make the mistake of thinking you can keep all the information in your head. Take notes so you are not starting from square one each time you attempt a bigger brew.
• Have a coffee shop grind your coffee (gasp)- If you don’t have a very good grinder don’t fight it. Stop by your local coffee shop the day before and explain your situation. They can, not only help you with a recipe but will be able to use their more expensive grinder (Note: this is best deployed at a quality third-wave coffee shop that does pour-overs)
• Shrink your batch size- If you are finding your big batches inconsistent and taking forever to filter, shrink your batch size. There is nothing wrong with brewing multiple smaller batches of coffee. You can either dispense the coffee as it is ready or brew a second batch on top of the first in your Chemex (rinse both filters at the beginning).

Most Importantly don’t let the pursuit of perfection rob your joy

Phew, that is a lot of information on something I was just going to write an addendum on last week. Sometimes you don’t know how much you have to say about something until you sit down and think about it. If I lost you somewhere among all the technical discussion, this is where I want you to come back because it is the most important thing.

Do not let the pursuit of perfection rob your joy!

Sharing your passion for coffee is a fun thing that brings community, don’t spoil it by obsessing over every little thing. The greatest weakness of brewing large batches of coffee (it’s large size) also happens to be it’s greatest strength.

I have yet to brew a large batch with good coffee that was undrinkable. The mistakes are compounded by the batch size but in the end, they are also somewhat diffused. Have fun, enjoy sharing coffee with the people around you and use mishaps as a way to discuss some of the intricacies of brewing a cup of coffee. It isn’t worth getting bent out of shape over, enjoy yourself.