Last time we looked at immersion brewing we put the most common brew methods to the test to look at the temperature profiles of each and gauge their impact on the cup - namely how sweet they were.
After noting such a spread in sweetness across these different brews that ranged in temperature from roughly 185f-140f with brew times ranging from 4 minutes to upwards of 10 minutes it became evident that there was more we could learn more by digging even deeper.
There are a few lesser-explored areas within coffee brewing. The t.d.s range 2-7% being one of them, and another being the interplay between time and temperature when times range beyond minutes into hours and temperatures drop out of the commonly accepted range of 195f-205f down to as low as 55f. The explosive interest in “cold” brewing over the last few years represents how a lot of these interesting concepts are being readdressed in brewing at the moment. We’re seeing techniques of brewing between 12-24 hours using medium-to-coarse grind sizes with brew temperatures from 55-80f or even exploring hot brewing and flash chilling, similar to a scaled up Japanese iced-coffee method.
To satiate our curiosity we set up another comparative brew test to cover the middle ground through 15 different brew samples, 3 brew ratios, and 5 different time and temperature profiles. Our temperatures ranged between 140f-55f, and our brew times from 1 hour to 16 hours exchanging temperature for time to cover new ground part 1 couldn’t with classic methods. For this series we’ve chosen to brew with Anthem, our most progressive blend comprised of the only two origins boasting fly crops: Colombia and Kenya. We’ve used brew ratios of 12:1, 13.5:1, and 15:1 with all samples being ground on a medium-fine setting using our Ek43 with coffee burrs.
TEMPERATURE AND TIME PROFILES
Having learned from Part 1 that lower temperatures extract at a slower rate than higher temperatures, each of the 5 profiles exchanged a lower brew temperature for a longer brew time. Similar to part 1 the extraction levels of the samples were reasonably close to our targeted window of 18-22%. Though, what we were tasting within those extraction levels was very different depending on how we got there.
Shown above are the extraction levels of each temperature profile across the 3 brew ratios.
More than arriving at specific targets our hope was to observe a trend in the profiles. Fortunately we observed one in both the data and from a taste perspective. The highest extractions were awarded to the highest brew temperature of 150f-110f over one hour, and to the longest brew time of 16h with the higher temperature of the two, 72f-67f. These two high points had a very wide spread in sensory attributes so our extraction data has told us objectively how much flavouring material was in each cup but not the balance of constituents that could be found, or what has happened to them over time once extracted.
The natural follow up to this was trying to figure out why we tasted the trend we did. We know from part 1 that longer brew times pull out more sucrose when a temperature is held constant; and that higher temperatures extract all compounds more efficiently. We've turned to the work of Ted Lingle to help us look at the dissolution rates of several key acids and compare them to the saturation point of sucrose at various brew temperatures. His work in this area reflected brew cycles of 10 minutes and although ours are quite a bit longer it has helped substantiate the sensory trend we found.
The acids graphed on the right have their total extraction levels listed in brackets beside the temperatures that dissolved them. Similar to our sensory trend they decreased along with brew temperature. The columns show you the percentage of the total extraction yield these acids can claim. There is predictable decline in the rate of extraction when brewing from 200f-120f, but an interesting drop in efficiency occurs between 120f and 110f. Here caffeine, phenolic compounds, trigonelline, and chlorogenic acid (which at high holding temperatures break down into caffeic and quinic acids, creating bittering and stale qualities) extract at a uncharacteristically lower rate than at even 10 degrees higher. On the left we've shown that the saturation point of sucrose at various brew temperatures is quite consistent. One theory as to why profiles 2 and 3 were preferred is that, when brewing below 120f the extraction rate of these key acids slows while the extraction rate of the sugars remain on their consistent downward trajectory; effectively creating a new extraction behaviour in this temperature range that given enough time allows sucrose to become the dominate constituent.
A few excerpts of text around his tables built our confidence in this being a plausible occurrence.
Colour in the Coffee Brew (pigmentation/caramelized sugars)
“Caramelized sugars represent the largest category - about one-half of water-soluble material found in the coffee beverage. From a taste standpoint, they contribute to the overall perceived caramel-like taste of the coffee beverage.”
“Pigmentation (often referred to as colour) is an approximation of the amount and degree of caramelized sugars entering the extracted beverage.”
An interesting note was made that profile 2 (even more so than 3) was darker and clearer in colour.
Temperatures effect on Taste
“Second to grind, temperature has the greatest influence on the brew’s taste attributes. Sensory evaluation shows that both acidity and body increase when the coffee is brewed at higher temperatures, whereas bitterness and astringency decrease with lower temperatures.
“Table 4 also suggests that the bitterness and astringency experienced in over-extraction results from a build-up in the concentrations of chlorogenic acids and phenolic compounds during the later stages of the brewing process… The exact causes of the flavour change created by over-extraction are currently not known.”
Other Brew Components
“A comparison of extraction rates for a 2 minute contact time showed the highest rate for trigonelline, followed by caffeine, soluble solids, chlorogenic acid, phenolic compounds (originally and incorrectly classified as tannins), and colour. Therefore, it appears that extraction proceeds more rapidly for trigonelline and caffeine under normal brewing conditions than for other components.”
A commentary on early extraction behaviours within the advocated 195f-205f temperature range.
“Extraction rates for each compound increased with increasing temperatures of extraction...Extraction rates decreased in the following order: trigonelline, caffeine, soluble solids, chlorogenic acid, phenolic compounds, and pigmentation (color)”
Remember that pigmentation is our approximation of the amount and degree of caramelized sugars entering the extracted beverage and that they tapered the least as brew temperatures declined when compared to the other compounds listed.
This adds credibility to the theory that as you lower your brew temperature below 120f you will create a new extraction behaviour that further decreases the rate at which these key acids are extracting (chlorogenic acid and phenolic compounds potentially being the drivers of “over-extracted” taste attributes) while retaining the extraction efficiency of the caramelized sugars.
These are some interesting concepts to consider when exploring uncommon approaches to temperature and brew time. There are hundreds of compounds in brewed coffee so although we’re looking at several of the major flavour contributors there is more that is unknown than known. The ultimate take away has been that there is still much to be explored and that using our sense of taste as our primary tool can lead us into an unexpected and exciting new areas.
If you are addressing these areas in your brewing or have any questions or ideas you want to contribute, let us know!
Yours in Coffee - Pilot.