In the past few years, cold brew coffee has become increasingly popular among specialty coffee drinkers and consumers more widely.
Cold brew is generally made using room temperature water (around 20°C or 68°F), which eliminates acidity in the cup and brings out the sweetness and body of the coffee. This is in contrast to most “traditional” coffee brewing methods, where the water should generally be heated to a point between 90°C and 96°C (195°F to 205°F).
But what about brewing with warm water? To find out if it’s possible, how you can try it, and what it tastes like, I spoke to three baristas. Read on to find out what they said.
You might also like our guide to cold brew summer cocktails.
Brewing coffee with warm water
Pedro Foster is a barista and roasting consultant and instructor. He also founded Fuzz Cafés, a microroastery in Rio de Janeiro, Brazil, with his brother João and coffee consultant Sérgio Kienteca.
Together, they have been experimenting with what they call “warm brewing” since 2017. After hundreds of tests and years of experimentation, they recently launched a multi-filtered coffee concentrate, brewed with warm water.
But to understand why someone would brew coffee with warm water, we must first look at the process of extraction in more detail.
“Roasted coffee is a stable bean that carries a lot of flavours and aromas,” Pedro says. “In order to trigger extraction from the bean, we need two things: energy (generally heat) and time.
“We then tweak different parameters to decide what we want from the grounds, using some key variables involved in the process: temperature, time, and the preparation method in question.”
Essentially, the more energy you use, the less time it will take to extract the soluble flavour compounds in your ground coffee. This is why traditional filter coffee only takes a few minutes to brew at high temperatures (around 90°), but cold brew can take up to 24 hours.
Temperature & flavour
Mari Mesquita of BikeBrew is a barista, cold brew specialist, and quality consultant based in Brasilia, Brazil.
She says that warm water brewing should not be understood simply in terms of how long it takes. Instead, she says it highlights the sheer number of variables involved in the process of brewing coffee.
As filter coffee is brewed at a very high temperature, there is more energy available and extraction occurs quickly. However, different flavour compounds are only extracted at certain temperature points.
For example, at higher temperatures, the flavour compounds typically associated with acidity and other, more delicate or subtle tasting notes start to emerge in the cup.
“[Cold brew] is extracted over a long period of time, between 6 and 24 hours, maybe even longer,” says Mari.
However, because of the lower temperature, there is less acidity in the final cup. Instead, the flavour profile tends to be sweeter and smoother, with a heavier body and mouthfeel.
Sérgio from Fuzz Cafés tells me that because of the temperature range between cold brew and typical filter coffee brewing, the outcomes are more varied. Consequently, you can incrementally change the temperature to experiment.
“When we work with medium temperatures, we can choose what we want to keep or take from the cup.”
Can we really compare cold and hot brewing to warm water brewing?
We know that brewing with hot, warm, and cold water leads to vastly different results. But just how does this alter the final cup profile?
According to Mari, there’s still no conclusive answer.
“Warm brewing is widely understood on barista forums as a ‘quick’ cold brew,” she says. “I think that both methods [cold brew and warm brewing] are now very susceptible to different interpretations because we don’t have a strong tasting repertoire yet.”
She also notes that it is difficult to compare the different methods. “Any extraction must come from the understanding that this is something dynamic, that each coffee compound is extracted at different times and under different temperatures,” she says.
“However, there is a very big difference between the chemical presence of the acidity and the sensory perception of it,” Mari tells me. Ultimately, warm brewed coffee is a middle ground between cold brew and regular filter coffee; it is more acidic than the former, but less than the latter.
Similarly, by changing the steeping time, you can balance other parameters to increase or decrease the extraction of different flavour compounds.
So, why brew with warm water?
“Why not?” replies Mari. “If it looks like there’s no limit to the flavours I can extract in the cup, I’ll try it.”
Warm water brewing has been gaining interest precisely because of the possibilities. There’s also comparatively little research available about it. The variance in temperature allows brewers to tweak the characteristics and flavours they taste in the final cup – higher or lower acidity, for instance.
“The great merit of warm brewing is the power of choice,” Sérgio says. By lowering or raising the temperature and exposing the grounds to water for more or less time, you can highlight specific flavours.
Mari encourages baristas, coffee shop owners, and coffee professionals to consider brewing with warm water.
“If it is good and I make something fantastic with it, I can present a different extraction method that does not involve the time and logistics of cold brew, for instance.”
She also says that the more people try it, the more accessible it will become. In time, this will drive more people to explore it as a possibility and raise quality.
“The advantage of the warm brewing universe is that you can learn from other beverages, like beer brewing and cold brew,” she adds.
How to brew with warm water at home
Sergio suggests using the French press as a starting point. This is his home recipe:
- Coarsely ground coffee (the same grind size you’d use for a regular French press)
How to brew:
- Add coffee and water to a French press at a ratio of 1:4.
- Place a saucepan full of water on the stove and keep it on a low heat.
- Place the French press in the saucepan. The heat will transfer into the vessel.
- Try and maintain a water temperature of around 45ºC.
- Allow the coffee to brew for up to four hours.
- Stir regularly.
- Once brewing is complete, strain the grounds out using a paper filter. Sérgio doesn’t recommend using the French press plunger, and notes that a paper filter will provide a cleaner cup.
Tips for a successful brew:
- Don’t have a kitchen thermometer? Use your hand. The water should feel a little hotter than your own body temperature.
- Taste as you go. You might find that you don’t need the full four hours.
- To maintain the temperature, you can either use the stove or top the saucepan up with warm or boiling water.
What does it taste like?
Like with other extraction methods, it’s hard to define a specific sensory profile for coffee brewed with warm water, especially considering the sheer number of variables involved.
There is a scientifically proven correlation between high temperature and the extraction of acidic flavour compounds. Based on this, coffee brewed in warm water should be less acidic than hot pour over coffee, but more acidic than cold brew.
Pedro says: “[The final cup profile] depends on the coffee you have, the roast, time, temperature, and sensory profile. Depending on how I lead my extraction I can highlight, balance, or hide some attributes from the coffee I have.”
As a test for this article, Mari Mesquita brewed the same coffee separately using warm and cold water. The grind size was the same for both, as was the 1:5 coffee to water ratio.
For the warm brew, she put the coffee in “total infusion” using a thermocirculator (sous vide), without using a filter to separate water from coffee. The solution was immersed at 50ºC for 45 minutes, and then filtered using a V60 dripper.
In contrast, the cold brew was made with room temperature water and placed in the refrigerator for eight hours before also being filtered using a V60.
She evaluated the cup profile of both brews, looking at aroma, flavour, acidity, sweetness, body, and aftertaste.
“The coffee brewed in warm water had an aroma much more similar to what I get from hot brewing,” she says. “I felt the sweetness right away, including notes of cocoa.
“With the cold brew, I felt more sweetness and there was a longer finish, but I tasted notes of malt. The cold brew had a medium and smooth body, whereas with the warm water brew, I had a lighter body.
“I realised that the finish for the cold brew lasted longer than the coffee brewed in warm water. However, the warm water brew brought out more acidity (albeit still less than hot water), giving it a refreshing characteristic that enriches the drink. It’s a nice balance of some muted acidity and more body than a regular filter coffee.”
As it is not yet a mainstream concept, there’s still a lot of unexplored ground for warm water brewing.
“We still need to understand, for instance, how the temperature in extraction influences the beverage’s lifespan,” Pedro says.
Mari agrees that temperature is the best place to start.
“The definition of warm has always been subjective,” she says. “Hot and cold are sensations that you can identify more easily, but what can actually be considered warm?”
She says that the next step is for coffee professionals to experiment with a wider range of “warm brew” temperatures, while other market stakeholders explore things like shelf life.
Even with so many unanswered questions, however, the interviewees see great potential for this method.
Pedro adds: “[It could be] a base for other products, new recipes, in beer brewing, or as an ingredient for culinary products.”
Warm water brewing is in its early stages in the coffee sector. This means that there is space for it to be refined and even perfected.
Nonetheless, it could still certainly be a source of excitement for the specialty coffee sector. It represents a new possibility for unusual and unique cup profiles, and is another area where both home brewers and coffee professionals are innovating.
Enjoyed this? Why not try brewing your own cold brew coffee?
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