As the summer heat continues into September, many coffee lovers have been turning to iced coffee and espresso drinks.
Articles are being published frequently on the subject, even by well-known sources such as the New York Times.
Even though there are a lot of guides to making iced coffee online, there aren’t many that go into detail about how it differs from the traditional way of brewing coffee and espresso.
Heat vs. Cold
When brewing coffee or espresso, it is important to understand the fundamental differences between high and low temperatures.
When making coffee, two things to consider are how the coffee will Extract with heated water versus cold water, and how the coffee will taste when hot versus cold.
Brewing temperatures
Hundreds of years of scientific study of the process of extracting coffee from ground beans has found that there is an ideal temperature range for making a well-balanced, good-tasting cup of coffee (or espresso).
We denounced an article recently from 1918 that talked about the importance of pretty precise brewing temperatures close to (but not exceeding) water’s boiling point.
Water used to brew coffee should be around 195-205F. This is based on the type of beans, roast, age of the coffee, and brewing environment.
This temperature is too high because it causes the extraction of bitter-tasting components that can affect the taste and smell negatively. If the temperature is too low, you will be able to taste the sour flavors more, which will limit the amount of sweetness that you can taste in the coffee.
So, if lower water temperatures produce sours, why would anyone brew with cold water? Wouldn’t that just amplify sour tastes?
Not necessarily, because traditional cold brewing is done. We’re talking about things like how long the coffee grounds are exposed to hot water, how heat (or lack thereof) causes different reactions in the coffee, and more.
Hot brews usually take place over a range of 60 seconds to upwards of 5-8 minutes, but cold brew coffees are usually produced using much longer extraction times.
The Toddy method of coffee brewing is a slow extraction process that uses a large vessel of water and ground coffee, left to sit in a refrigerator for a day. This method extracts residual sugars and mutes acidic content, which would otherwise be extracted with hot temperatures.
Ice drip brews require a lot of time, sometimes as long as 4 hours or more. The water is slowly released in controlled drips, sometimes as slowly as one drip per second.
This brewing style uses a flow through method, which takes hours instead of minutes.
The general consensus about ice brewed or cold brewed coffee is the following:
- results in a low-acid cup. Some people refer to this as a soft cup or mellow cup, with virtually no bright acidity present in the taste, even when using notoriously high-acid coffees like Kenyas or brighter Centrals.
- cold or ice-brewed coffee has a bit of a shelf life, unlike traditional hot-brewed coffee does. Some very experienced palates in the world of specialty coffee claim that cold or ice-brewed coffee can be kept in the refrigerator for up to 72 hours or more. My opinion, based on taste, is it has a 24 hour shelf life.
- the coffee can be produced in a more concentrated format since the extended brewing times can lead to greater overall extraction and form a more concentrated brew. We’re not talking espresso concentration levels here, but as much as a 2:1 ratio or more compared to the normal viscosity and taste of a hot brewed cup. This allows for more dilution with ice while still retaining a good viscosity and depth to the beverage.
- body-rich coffees (heavy on spices, chocolate notes, etc) tend to do the best in cold and ice-brew coffees; that said, fruity-acidic coffees also do well because the fruits can sometimes carry through to the cup while leaving behind the acidity. Some people refer to these brews as “juicy tasting” cups.
Iced coffee: Keep the heat, then chill
Ice brew coffee is a type of coffee that is brewed using the “Japanese iced method.” This method is similar to regular coffee brewing, but the coffee is brewed over a cup of ice instead of hot water. This results in a coffee that is less acidic and has a lower caffeine content. It uses classic devices like the Chemex, V60, or AeroPress, but the recipes are rearranged by adding ice early.
(State, 2018) When coffee is freshly brewed and hot, it is cooled instantly when it is dropped on ice drop by drop. Your coffee will be cold, full of flavor, and ready to drink as soon as you finish making it.
This method answers some longstanding concerns about coffee served cold:
Iced coffee requires a ton of grounds, right? Not this coffee. Instead of producing a concentrate that has to be cut with milk or water, the goal here is to produce a final product that is drinkable without any further additions.
We recommend that you use a moderate amount of beans, but there is no need to use an excessive amount. To make cold coffee, you don’t need to change the regular coffee to water ratios.
How can this coffee be anything but diluted? If you want your coffee to be stronger, use more coffee grounds than usual. The coffee cools faster and doesn’t melt as much ice when you introduce it to ice drop by drop.
Pouring a cup of hot coffee over ice all at once will result in quick ice melt, as well as the ruin of the coffee for the person who was looking forward to a nice, cold drink.
The iced coffee at restaurant chains is often bitter and flavorless. This is the result of a devastating chemical phenomenon called oxidation, which takes place when coffee sits for a long time and is exposed to oxygen in the air. It elevates the conversation to a higher level, specifically discussing science. Lab coats on.
Unlike humans, coffee does not like oxygen. In fact, coffee and oxygen are sort of enemies. It turns out that oxygen is an oppressive element that ruins the naturally occurring oils in coffee, making them taste unpleasant.
The longer coffee is left to go bad, the worse it will taste. If you’re brewing coffee at high temperatures, the oxidation process will happen more quickly.
“It’s essential, then, that iced coffee, when brewed hot, is cooled as quickly as possible. Brewing directly over ice achieves this wonderfully.”
But this chemistry lesson isn’t over just yet. In his endorsement of this brewing method, Peter Giuliano of Counter Culture Coffee and the SCAA Symposium, offers a few more helpful terms.
The terms ‘solubility’ and ‘volatility’ will be helpful in this discussion.
The solubility of coffee describes how well it dissolves in water. This is important in brewing because coffee needs to be completely dissolved in order to extract all of the flavors and aromas. The changes in the water’s color (from clear to dark) are due to its increased solubility.
At higher temperatures, coffee should be brewed with water between 195 and 205 degrees Fahrenheit.
If you brew at temperatures below this range, you will not dissolve all of the solids that you want to. (But more on that later.)
Volatility is a term used to describe a substance’s ability to vaporize. In the world of brewing, this term is used to describe coffee’s ability to go airborne. Volatility refers to the ability of a substance to change from a liquid to a gas.
At high temperatures, the volatility of coffee increases, which causes the aromatics of coffee to be released. By brewing with hot water and cooling quickly, the aromatics of coffee can be recaptured.
Ice brew has received a lot of attention from the industry because it is very effective. It is easy to understand, comfortable, and supported by both experience and research, which is always enjoyable.
George Howell has described making cold brew coffee as “the only way to do it” and Jason Dominy praises it for retaining the taste of regularly brewed coffee.
Giuliano remarked that the same aromatics he was used to smelling in hot coffee, he could taste in iced coffee.
Crash-cooling: No dilution, no problem
What if we could brew coffee without worrying about diluting it by using the “Japanese” method?
The answer is clear and straightforward, but the execution is often clumsy and inefficient.
Just brew your coffee like normal, but use a vessel that conducts heat well, like a stainless steel cocktail shaker or large steaming pitcher. Then put it in a cold place.
The freezer can cool your beer, but it will take about an hour. This is not ideal if you’re in a hurry or if you want to avoid oxidation.
We recommend that you place your cocktail shaker in a container full of pulverized ice, add just enough water to cover the ice, and gently stir your coffee.
In about two minutes, you can have delicious and refreshing iced coffee.
It’s best to brew at a slightly higher strength than normal when making cold brew coffee, because we tend to lose some of our sensitivity to taste as liquids get colder.
The volatility, or evaporation rate, of cold liquids is lower than that of hot liquids, meaning that the delightful aromas we appreciate in hot coffee are not as present when cold. Adjusting the strength slightly upwards helps to make up for this, resulting in a tastier, sweeter drink.
The Coil is a device made to crash-cool your coffee without diluting it.
The stainless steel coil surrounded by ice water helps your brews cool as they flow into the carafe. The design of this product is similar to that of a wort chiller, which is a device used in the brewing of beer. This product has been miniaturized and designed for single-serve use.
This is one of the first products on the market that is specifically designed to cool coffee quickly, and there are probably going to be more similar products available soon.
Crash cooling coffee is not very common currently, but it is easy to see why it is a desired cooling method for coffee. It is probable that it will become more popular in the next few years.
So getting back to the question of sour coffees. The colder you brew coffee, the less sour and acidic it will taste.
The taste of coffee is affected by the temperature of the brewing water. Different elements in the coffee are extracted at different levels, depending on the temperature. Additionally, different temperatures can either cause or prevent chemical reactions from occurring in roasted coffee beans, which have a complex genome.
It’s possible that when you brew coffee at 180 degrees Fahrenheit, the acids don’t interact enough with fats and lipids to create a pleasant acidity. Instead, they come out as sourness. The perfect temperature for fats, lipids, oils, sugars, and acidity is 198F.
Take it down to 40F or colder, and different things happen – oils don’t boil; fats don’t liquify, but acids never move a micron or change to another state, resulting in a low (or no) acidic taste and the non-boiled oils result in a creamy, mellow taste that does get extracted.
Conclusion
We all approach our favorite iced coffee recipes in the same way, putting all of our energy into creating the perfect brew.
Thank goodness the caffeine takes effect then! We’re usually known for being fixated on details and having a strong preference for procedures with definite methods and dependable outcomes. To us, making coffee is just as much of an art when it is served cold.