The temperature of the water for brewing coffee is an important factor that is indispensable to create the quality of coffee flavor.At different times in the past and in many cultures, coffee was mostly boiled with water to form a thick, black, and bitter drink. With the coffee tree’s journey to conquer the world, we’ve found better ways to make it. With useful scientific knowledge, a traditional belief has been established that coffee must be brewed in hot water. And never, in history, has coffee tasted better than in these decades; In the third wave, however, art in contrast to science recognized cold brew as a way of drinking coffee without the need for heat.
Why make coffee with hot water?
These days, the popularity of cold brew has made all the basics of making coffee in hot water questionable!
Heat is perhaps the most common form of energy used to make coffee. And there are two reasons for this; First, the hotter an object, the more energy it has. Therefore, the hotter it is, the more molecules (or atoms of matter) vibrate (i.e. the greater the kinetic energy); Second, temperature follows the energy transfer rule, going from molecules with high energy to molecules with less energy.
This applies to brewing coffee in two ways. First, the higher the temperature, the higher the kinetic energy of the water molecules. As a result, they are more mobile which increases their ability to remove compounds from the coffee beans due to stronger physical forces – Simply put, the temperature helps to dissolve the coffee in water better (more details below). Second, heat from the water is lost during extraction due to heat conduction through the coffee, the brewing equipment, the environment, etc., so hot water provides compensation for the coffee to remain hot enough after it’s finished. phase – this is really important, right here.
Because the right water temperature will help you feel the flavors from the coffee better. If the temperature is low, the coffee may taste thin (low viscosity), flat, and have low flavor intensity. As the temperature increases, the molecules dissolved in the extract increase their activity, resulting in a clearer, richer, and more refined taste. Normally, cold coffee will have a more bitter and sour taste. However, it is not actually the bitter or acidic substances that increase, but because the familiar flavors are then reduced inactivity, allowing the sense of smell and taste to be more perceptible than other flavors.
The best temperature for brewing coffee
Finally, what water temperature is enough to extract all the flavors in the coffee in a balanced and delicious way? Although that decision is up to the individual, over half a century of research has determined that most people prefer coffee that is brewed with hot water around 90 to 96°C (range 194 -205 °F).
Although the suggested temperature of 90 – 96°C can be found in many scientific papers & articles. However, it was first published in 1950, by Dr. Earl E. Lockhart (SCA). Since then, this temperature bracket has been featured in SCA’s brewing manual to date.
This desired temperature range is slightly below the boiling point of water (100 ° C at standard pressure). If the temperature is too low, some key compounds will not be extracted effectively and all the desired flavors will not be obtained, high temperature will favor the extraction of insoluble compounds – Like As depicted in the chart below, the bitter, astringent, phenol compounds are soluble over a very high-temperature range and affect the overall flavor balance of the coffee.
Master the taste with temperature
As mentioned earlier, the efficiency of the extraction process depends on the solubility of the extracted molecules. Accordingly, the solubility of most compounds in coffee usually increases with temperature. However, this relationship does not always “increase” linearly in all cases. As shown in the following figure, while citric acid has a linear solubility increase with temperature, the solubility of caffeine quadruples between 80 and 100 o C. In other words, within that narrow range, Small temperature changes have a significant effect on the solubility of this compound. Therefore, the solubility ratio between citric acid and caffeine will vary depending on the water temperature.
This also explains why coffees extracted at low water temperatures (eg, cold brew) often lack strength due to less total dissolved solids as well as lack of solubility of compounds. strong impact on taste. However, this can be partially compensated by a much longer extraction time (more details below).
Another effect of water temperature is more physical in terms of temperature, the higher the temperature, the lower the viscosity of the water. The lower viscosity means that water can easily penetrate the coffee bean structure and enter the spaces (even within the fibrous cell structure) to dissolve the compounds present in the coffee. get high. This effect explains why the amount of oil (lipid) in coffee increases with increasing water temperature.
Volatile compounds & water temperature ?
For volatile compounds things are a bit more complicated, and it involves several other laws of physics. To put it simply, the solubility of a gas also depends on the water temperature, but vice versa for a solid. Consistent with Henry’s law, rising temperature causes gas molecules to enter the gas phase (evaporation). Therefore, the aroma compounds in coffee will be released into the air during the extraction process, the higher the temperature, the more aroma will be lost . Of course, spreading coffee aromas during extraction (and soon after) contributes to overall taste perception and experience, but reduces their concentration in the cup.
Cold-brew & nitro brew;
What about cold brew, nitro coffee, they are considered part of the specialty coffee movement? and have almost nothing to do with the water temperature in the extraction process.
To be clear on this, if coffees are brewed with cold water, they certainly lack the temperature to extract some of the low polar compounds (like coffee oil). The more polar compounds do not “hold up” at low temperatures and are still extracted fairly well. However, a longer extraction time (8 to 24 hours) is required, to allow a sufficient amount of flavor. On the other hand, the loss of volatiles during extraction is much less than during hot extraction, leaving these aroma molecules “trapped” inside the beverage. As a result, cold coffee yields a beverage that is surprisingly different from traditionally hot brewed coffee, given that the time required for extraction is longer.
The long-brewing time in cold brew can cause the coffee to oxidize, so exposure to air must be strictly controlled during extraction.
Finally, the article is quite short, but is long enough with a content that does not revolve around the focus of the coffee bean. Since it’s always been a fact that, the more we try to understand the coffee bean, the more complicated it becomes, so understanding brewing at its most basic will help us make a more informed decision to have a good coffee. suitable coffee cup.