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Why is thermal stability necessary for handbook espresso brewing?

Water temperature performs an necessary function in handbook brewing. Based on the Specialty Espresso Affiliation, to correctly brew high-quality espresso, your water needs to be between 90°C and 96°C (195°F to 205°F).

Nonetheless, alongside this, your brewing water also needs to stay at a secure temperature all through your entire course of. This can be a idea referred to as thermal stability – a necessary a part of handbook brewing.

Whereas temperature-controlled kettles can definitely assist to enhance thermal stability, your brewer additionally has an impact on it.

To study extra about how one can preserve a secure brew temperature, I spoke with two espresso professionals. Learn on to study extra on why thermal stability is so necessary. 

You may additionally like our article on how your dripper materials impacts your pour over espresso.

steadfast manual coffee brewer and gooseneck kettle

What’s thermal stability?

There are numerous variables to maintain monitor of when brewing filter espresso. These embody espresso to water ratio, complete brew time, grind dimension, agitation, and extra. Temperature, nonetheless, is among the most necessary.

When espresso is brewed, a variety of soluble risky compounds that contribute to flavour – comparable to oils and acids – are extracted. Nonetheless, as totally different compounds are extracted at totally different temperatures, guaranteeing that you simply hold your temperature secure all through the brew is vital. 

Hyunhwa is the Head Barista at Nothin Espresso in Seoul, South Korea.

“Thermal stability in handbook brewing means extra consistency in your extraction,” he tells me. “Consistency helps to mirror the espresso’s inherent flavours and allows you to put together the best-tasting espresso.”

Any vital temperature fluctuations (3°C in both course is important sufficient) can lead to both too many or too few compounds being extracted. Both method, this could have a notable influence on flavour.

If brewing temperatures are too excessive, the water extracts extra risky compounds, in addition to rising the speed of extraction – thereby lowering the whole brew time. 

This makes it more durable for the brewer to regulate the extraction charge, and can lead to overextracted espresso, which tastes bitter and hole.

Decrease brewing temperatures, in the meantime, lengthen the extraction course of because the water molecules have much less kinetic power, which means that they transfer round much less. In case your water temperature is simply too low, you danger underextraction, which suggests your espresso will style bitter and astringent.

Furthermore, if the espresso mattress is extracted with brewing water which isn’t at a secure temperature (for instance, if the temperature of water decreases over the course of the brew time), a few of the espresso grounds could also be extracted greater than others. This results in espresso which is each underextracted and overextracted on the identical time.

electronic gooseneck kettle maintaining temperature stability

Explaining thermal stability

Whereas sustaining thermal stability throughout handbook brewing may appear simple sufficient with the help of tools like a temperature-controlled kettle, it will possibly truly be harder than you would possibly assume. 

That is usually due to the form and materials of the brewer.

Hyunjun Kim is the co-founder of Nothin Espresso and predominant developer of the Steadfast filter espresso brewer.

“The huge opening on the high of an ordinary filter espresso brewer permits extra warmth to flee into the encircling air, slightly than retaining it within the slurry,” he explains. “Due to this fact, handbook brewing is extra liable to warmth loss throughout extraction. 

“This implies the fabric of your brewer tremendously impacts thermal stability,” he provides.

Totally different supplies used to fabricate filter brewers have totally different thermal plenty. Thermal mass is a measurement of how a lot warmth a fabric wants to soak up earlier than its temperature will increase. 

Supplies like concrete and stone, as an illustration, have a excessive thermal mass, as a result of they should soak up numerous warmth earlier than their temperature rises. 

“A filter brewer with a better thermal mass requires extra power from the brewing water, which it absorbs via warmth,” Hyunjun says. “This implies it takes longer to heat up.

“However, supplies with a decrease thermal mass require much less power to heat up, and so they soak up warmth out of the slurry far more shortly.”

Hyunhwa, in the meantime, emphasises the significance of utilizing a dripper which is produced from supplies that can retain warmth for longer. It is because brewers which lose warmth shortly can disrupt the temperature of the water, and due to this fact have an effect on extraction.

“Sometimes, metal conducts warmth a lot sooner, whereas plastics soak up and emit warmth at a slower charge,” Hyunhwa tells me. “Which means that, typically talking, plastic filter drippers are extra insulated than steel ones.

“Nonetheless, specially-insulated steel brewers like Steadfast conduct and retain warmth extra successfully for the very best thermal stability.”

steadfast coffee brewer with person drinking coffee

Evaluating totally different brewer supplies

We all know totally different supplies have totally different thermal plenty, and due to this fact we all know that they conduct warmth at totally different charges.

However how vital is the distinction? And what else must you take into account for thermal stability?


Hyunjun tells me that almost all plastic brewers are produced from “a spread of polymers, generally methyl methacrylate, which can be generally known as acrylic”.

Plastics have a excessive thermal mass (round 3 times that of metal), which suggests it takes longer for the fabric to soak up warmth from the brewing water.

In truth, plastics emit warmth round 20 instances slower than different supplies, which helps to keep up a secure brew temperature for longer durations. 

Ceramic and porcelain 

Hyunhwa says ceramic and porcelain are widespread supplies for handbook brewers due to their “excessive insulating qualities and visible enchantment”.

Ceramic has a barely decrease thermal mass than plastic, which additionally makes it materials for guaranteeing thermal stability.

Nonetheless, since ceramic is a dense materials, it absorbs extra warmth than plastic, even on the identical temperature ranges.

“Ceramic brewers soak up round 4 instances extra warmth out of your brewing water than plastic ones,” Hyunhwa explains. 


Glass is one other widespread materials for handbook brewers. 

Alongside its visible enchantment, it additionally has a considerably decrease particular thermal mass than plastic and ceramic brewers, so it wants much less power to achieve the fitting temperatures for brewing. 

“Glass filter brewers additionally are inclined to weigh round half as a lot as most ceramic or porcelain ones,” Hyunhwa says. “This implies they’re extra insulated in relation to the water temperature.”


Metal has a really low thermal mass in comparison with different supplies, so it will possibly warmth up far more shortly. This implies it requires a lot much less time and power to achieve the optimum brewing temperature. 

“Nonetheless, due to the thinner supplies, metal brewers can soak up extra warmth from the brew and launch it into the environment,” Hyunjun says. 

On account of this, he recommends utilizing metal drippers for recipes which have a complete brew time of three minutes or much less. 

Nonetheless, Hyunjun additionally factors out that utilizing an insulated metal filter brewer, such because the one made by Steadfast, means taking much less power and time to achieve the perfect temperature, in addition to higher warmth retention over time.

“The Steadfast espresso brewer is produced from high-quality chrome steel (SUS304) and comes with an outer insulated leather-based jacket, which helps to stabilise the brewing temperature,” Hyunjun tells me.

“This implies it will possibly attain the goal temperature extra shortly due to the metal’s decrease thermal mass, whereas the insulated jacket improves thermal stability all through the brew,” he provides.

Hyunhwa explains that Steadfast not too long ago carried out a research to check plastic and ceramic brewers to their dripper.

“Among the many three brewers, the Steadfast reached the goal temperature the quickest, and maintained the temperature for longer,” Hyunhwa says.

He provides that alongside the insulated leather-based jacket, Steadfast can be particularly designed to keep up thermal stability throughout handbook brewing.

The dripper has a trapezoid wedge form, with partitions which slope at a 31° angle (just like a conical brewer just like the V60). This helps to not solely preserve brew temperature, but in addition improves movement charge throughout extraction. 

Steadfast brewing device

Are you able to enhance thermal stability?

Hyunhwa tells me that when filter espresso is brewed, warmth loss typically happens throughout the floor of the slurry, due to the huge opening on the high of the brewer.

“Due to this, we suggest preheating your brewer to keep away from dropping an excessive amount of warmth out of your brew water,” he provides.

Denser supplies like ceramic and plastic needs to be extra totally preheated than metal and glass, as they take longer to warmth up. This prevents them from absorbing an excessive amount of warmth through the preliminary phases of extraction.

In the end, utilizing high-quality brewers produced from sturdy supplies lets you obtain a constant, secure temperature when getting ready filter espresso.

“With the Steadfast, we targeted on comfort, sturdiness, and ensuring folks loved brewing espresso with the dripper,” Hyunjun says. “To realize all of this, we used SUS304 – a food-grade chrome steel recognized for its sturdiness – and a leather-based jacket produced from plant-based pure tannins.”

Steadfast devices on countertop in coffee shop

Your dripper materials undoubtedly has an influence on thermal stability and brew temperature, which in turns impacts extraction and the flavours you style in your cup.

When selecting a brewer, take into account the supplies you utilize and the way they will have an effect on thermal stability. By choosing a brewer with a decrease thermal mass, or one that’s insulated, you usually tend to preserve the required temperature of your brewing water.

This fashion, you possibly can concentrate on the various different extraction variables which can be necessary for getting ready high-quality espresso.

Loved this? Then learn our article on how temperature can influence your expertise of espresso.

Photograph credit: Steadfast

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Please observe: Steadfast is a sponsor of Good Each day Grind.

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