When you think about what affects the flavor and profile of your coffee, you’re likely to consider brew ratio, grind size, water temperature, and water quality. But did you know that the shape of your filter basket can also impact the flavor of your coffee?
Let’s find out more about how the geometry of a batch brewer basket or pour over filter holder can influence your daily cup.
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The Kalita Wave has a flat-bottomed base. Credit: Thomas Martinsen
Investigating The Impact of Basket Shape
Professor William Ristenpart is the director of UC Davis Coffee Center, where he researches ways to brew better filter coffee. He tells me that most commercially available brewers have either a flat-bottomed or semi-conical basket.
“Roughly speaking, half of them are flat-bottomed and about half are semi-conical,” he says. “However, what’s kind of been missing is any hard data to support any type of analysis of which is better. One of the questions we ask is: should we compare brew ratios for flat-bottomed versus semi-conical?”
But how do we determine which makes a better brew? It’s difficult to evaluate and compare quality. The Specialty Coffee Association (SCA) offers a Brewing Control Chart, which Ristenpart tells me he uses to help evaluate brew profiles. But he notes that this measure isn’t without its flaws.
“What is the difference, if any, in sensory properties of drip coffee when you use either a flat-bottomed or semi-conical filter basket? We put together a whole bunch of sensory tests to try to answer the question. The basic idea is to use everything the same: same coffee, same grind size, same water temperature, same everything, except for the basket geometry,” says Ristenpart.
His team found that basket shape does make a difference. “In terms of our sensory evaluation, basket shape made maybe even a more pronounced impact than the grind size did,” he says.
A Behmor Connected batch brewer. Credit: Behmor
Why Basket Shape Matters
Brewing coffee is essentially a controlled exercise in chemical changes. When we make a cup of coffee, we’re encouraging molecules to move from the coffee solids into the water.
“The nature of the fluid flow through the porous media (the coffee grounds) is influenced by the shape of its container (the basket). The container affects the degree of mass transfer that occurs. In other words, it affects how much extraction occurs,” Ristenpart says.
“If you have a flat-bottomed basket, water’s hitting it in the middle, spreading out radially, and then exiting through a hole or multiple holes also in the middle. That flow pattern is different if you have a semi-conical shape where it’s hitting it in the middle. It doesn’t spread out as much radially,” he says.
Learn more in Understanding Coffee Extraction For Your Perfect Cup
Behmor’s ground basket. Credit: Behmor
Of course, there are many ways that baristas modify the flow of water to impact the final profile of your coffee. When making a pour over, there are different pouring techniques including the circular pour, single pour, pulse pouring, and many others. SCA-approved batch brewers focus on distributing water evenly across the bed of coffee grounds to promote even extraction and limited temperature fluctuation.
The Coffee Center’s research shows that there are differences in profile between coffee made in a flat-bottomed basket and a conical one, and suggests that this is caused by the different ways water flows through the bed of coffee. But it’s possible to modify the water flow and therefore the final brew in either basket shape by changing the pouring technique.
A barista makes a pour over coffee. Credit: Jakub Kapusnak
Which Basket Shape Is Best?
So, which basket shape should you use? Like many things in coffee, it’s a matter of personal preference.
“When we had our expert panel do a sensory descriptive analysis of identical coffees, but brewed with either the flat-bottomed or conical, the panel pulled out very different flavor profiles. They noted more tea/floral-like flavors in coffee made using conical baskets and more smoky, tobacco-y, roasty flavors with the flat-bottomed,” Ristenpart says.
But he warns against overstating the importance of basket shape.“The first thing that controls the flavor is the quality of the beans themselves,” he says. “I don’t want you to come away thinking that the conical is always going to get more tea-like, floral flavors. That’s not true because it really depends on the type of coffee that was used in the first place.”
The Behmor Brazen batch brewer. Credit: Behmor
Making a good cup of coffee is a balance of many related variables. Your choice of basket shape may not be the most important factor in determining a coffee’s profile, but the evidence suggests that it does play a role.
So if you’re in the market for a new pour over device or batch brewer, or are unsure of what method to order at your local specialty coffee shop, keep basket shape in mind when making your choice.
Enjoyed this? Check out Coffee Science: Breaking Down Where Flavour Comes From
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