In case you haven’t read the original post on the flavor wheel that I posted back in September 2012, you should go read it here. At that time I focused mostly on how turbulence can bring out varying flavors but didn’t spend much time talking about the theory behind it. During the SCAA 2013 Expo in Boston I had the pleasure to meet Mr. Ted Lingle and ask him a bit more about the arrangement of the Flavor Wheel. He did confirm that the arrangement of the flavor wheel is done so according to the mass of the individual flavor or aroma compound. That is to say that as the colors increase in intensity from lightest (Coffee Blossom and Acrid) to darkest (Charred and Creosol) they reflect the molecular weight increase.
The discussion about mass of the compounds is important because, I believe, the flavor development of coffee during extraction is a result of two main components – time and turbulence. The amount of time needed is directly related to the density of the coffee. What I mean by this is that the denser the cellular structure of a coffee particle the more reluctant it will be to give up its flavoring compounds and thus will need more time. Density can be affected by several factors including, but not limited to, origin, processing, and roasting. As for turbulence, we know that it increases the rate of extraction but I theorize this can only happen to a certain threshold. I have expected to over extract coffees from time to time by using turbulence; however, I found that when measured objectively with a refractometer the extraction hadn’t increased but the flavor development had significantly changed.
Let’s step away from coffee for a moment and imagine something completely different. Say you have a pile of three components jumbled together and dumped out on the sidewalk – feathers, wood chips, and bits of broken pottery. There are two ways you can diffuse this pile of things out into the atmosphere of the air. One, you can leave it to time. The gentle breeze and people walking by will cause the feathers to diffuse first out into the atmosphere. The sun, wind, and rain will break down the wood chips and they will diffuse into the environment. And finally, after considerable time the pieces of broken pottery will no longer remain in the pile but will be distributed into the environment. The second way to move these items out into the atmosphere is to introduce an outside force – say a leaf blower. By adjusting the amount of time as well as the amount of force the leaf blower applies to the pile you can change how quickly some of these items diffuse into the atmosphere.
Now I know that’s not a perfect example because there is much more going on during coffee extraction but it is a good starting point. The “atmosphere” in coffee brewing is hot water. On a molecular level as you heat up water you excite the molecules and they begin to move around more rapidly. This closely resembles the wind and people walking by our pile of feathers, wood, and clay. However, in this case the pile is represented inside each individual coffee grind and our items are the three major divisions of flavors on the flavor wheel - sour/enzymatic, sweet/sugar browning, and bitter/dry distillation. The leaf blower can be any number of things that cause outside turbulence including manual stirring, water flowing into the slurry from a kettle or sprayhead, or air bubbles.
In my experience I have found that extraction levels, when measured objectively with a refractometer, have more to do with the overall extraction time. While it is possible to increase the rate of extraction by introducing turbulence I hypothesize that this rate increase only happens up to a certain threshold – meaning that you can only increase the rate so much by introducing turbulence. There are other variables that may increase the rate beyond what turbulence can do (e.g. pressure) but I find that even when a coffee has turbulence applied for the entire extraction period that measured extractions only increase slightly as compared to pulsing turbulence. This is important in understanding how turbulence affects flavor because we have often attributed the flavor development to be a “chance” thing that is related to time and intangible factors. I challenge that you can affect flavor development using turbulence without much shift in extraction because of the fact that flavors have different molecular weights.
All of this theorizing comes from my experience lately in manipulating coffees. One particular coffee that I’ve used recently is the Tairora Cherry Project Papua New Guinea by Counter Culture Coffee. This coffee is unique because it has rather high levels of all three major flavor categories which has made experimentation exciting. Below you can see three different trifecta recipes for the Tairora project. Green is my “Sour / Enzymatic” recipe, brown is the “Sweet Salt / Sugar Browning” recipe, and purple is the “Bitter / Dry Distillation” recipe. When brewed each of these coffees measures around 1.30 – 1.35 TDS and 19-20% extraction yield. However, the flavor development in each cup is significantly different.
The idea that more turbulence allows for more of the heavier mass compounds to be present in the cup means that each recipe has a shift in turbulence. All of the recipes have a 40 second extraction time but with slight increases (two second increments) in Fill Pause Time. The reason I increased fill pause time is that trifecta introduces turbulence during the pre-infusion stage so this is in turn increasing the time for turbulence. From sour to sweet I increased the amount of time of Turbulence On by 4 seconds per cycle (8 seconds total) and I also increased the press out pressure. The coffee went from exhibiting bright tart cherry characteristics to tasting nutty and sweet with muted acidity. Additionally from the sweet to bitter I decreased the time for turbulence but increased the turbulence power and temperature. With only a slight increase in extraction yield the flavor development changed significantly to become more of a Black Currant Like fruit and a slightly spicy aroma.
Don’t just take my word for it – try it yourself! I recommend starting by using immersion brewing for the experiment since turbulence is easier to control in an immersion brew than in a drip style brew. First, I recommend introducing stirring using a stopwatch at specific intervals while trying to maintain the same force of turbulence. Then brew the same coffee ratio, grind size, total brew time, etc. using either more time or more intervals of turbulence. Finally try it with turbulence the entire time or change up the force at which you apply the turbulence. If you have the ability to measure your extractions definitely do so, but only after you taste. I’d love to hear your feedback as to what you find.