Uel Brew 1000 cold brew action shot By Austin Patterson, Head of Innovation & CFO at Uel Zing Coffee
Cold brew, like pour-overs or espresso, is just another brewing method. We would not like to limit its possibilities by assigning too narrow of a definition. Fewer limits open the door to exciting exploration and the opportunity for discovery—all in a cup of coffee. If you are anything like us, every coffee you choose is accompanied by a feeling of anticipation and curiosity. It is an ultimate goal to assist the greater coffee community, especially those at home, to get more out of each bag that captures their attention. We wanted to take time to perform extended experiments to create a resource that aims to further our understanding of cold brew and coffee as a whole. What follows is meant to be a starting point for us and hopefully for you as well; Enjoy!
The refractometer reader and coffee-filled pipette
Our standard cold brew recipe was developed for a consistent bottle-able product that was easy to manage with a day-to-day workflow. We believe it brings out all of the right characteristics of our signature blend. But coffee via a 24 hour cold immersion is not the full extent of cold brew nor Uel Zing. We studied the effects of water temperature, stirring, and steep time on the flavor profile of our Zing Blend and other single-origin coffees to learn the common flavor results of the different preparation methods.
The three methods studied were our standard cold immersion, room-temperature immersion, ice-cold immersion, and finally cold immersion prepared with a hot bloom. The affects of stirring at different intervals were also studied across methods.
Samples pulled at several intervals throughout each cold brew experiment.
Stirring is used to accomplish two things: even saturation and increased rate of extraction. When used for the purposes of an extended immersion, as in this instance, the former is most important. This is because stirring does not appear to lead to a constantly increasing rate of extraction. More so, as shown in the diagram below, it offers the slightest bump in extraction but then eventually finds its way back to the baseline curve. When the immersion time frame is in the realm of hours this bump is not super drastic. Even saturation on the other hand will have a large effect on the TDS (total dissolved solids) and extraction of the coffee in all circumstances. It follows that when coffee is not fully or evenly saturated, it will not be fully or evenly extracted. This is the major reason why we stir, especially in large immersion batches.
So when and how does stirring affect cold brew? The effects of stirring appear to be consistent across preparation methods highlighted here. Stirring that occurs early on in the brew process, just after the water and coffee have been introduced, has the greatest bearing on the progression of the brew. This initial stir will set the stage for what is to follow. There is no set parameter for the duration of time you must stir, however it will increase as the batch size or ratio of coffee to water increase. This is due to the fact that as the mass of coffee increases in size or proportion to the water, it becomes more difficult for the water to make its way to the center of the mass and for the soluble particles in the center to make their way out into the solution that surrounds it. A general rule is to initially stir the brew until you feel all of the grounds are fully saturated, and then stir just a bit more.
Due to some other factors that we will explore in later posts, this early stage—when the water has its lowest TDS—is the most opportune time to stir and create an environment of even and full saturation. Stirring that occurs at later stages and at the end of the brew have insignificant effects on the final product. As it turns out, on a large scale, stirring later in the brew can cause the coffee to prematurely sink and compress the grounds leading to a negative outcome—weak cold brew.
From this we have concluded that a good stir at the beginning of the immersion process should be sufficient for consistently delicious cold brew.
Standard Cold Immersion
All of our cold brew to be bottled is prepared using a 12.5:1 brew ratio that starts with freshly ground coffee (coarse) and room temperature water. Once the brew is sufficiently stirred, it is placed in a cooler to steep for the next 24 hrs. This method starts with an initial extraction of around 9% and slowly climbs to its max extraction of about 21% over the 24 hrs. In terms of flavor and mouth feel this method tends to produce a well-bodied coffee with notes of chocolate highlighted by the accompanied sweetness and floral notes that may be inherent in your beans of choice. This lends itself very well to floral and fruity African coffees with not too much acidity, and naturals from most anywhere. Coffees with high levels of acidity can easily become overly tart or dry however.
This preparation followed the same brew ratio as the standard recipe but used water chilled to 37 degrees Fahrenheit. This method starts with an initial extraction of around 6% and slowly climbs to its max extraction of about 21% over the same 24 hrs. This small decrease in initial extraction leads to a noticeable decrease in sweetness, but the drinkability is not lost. The result is just a more one-dimensional coffee with smooth chocolate flavors.
This preparation used the same brew ratio and water temperature as the standard recipe but left the brew to steep at room temperature. This method starts with an initial extraction of around 9% and climbs to its max extraction of about 21% over the 14 hrs. The flavor produced by this slightly abbreviated steep time is earthy throughout. Those who enjoy the flavors of Indonesian and Sumatran coffees may also enjoy the flavor profile of this method.
Cold Immersion with a Hot Bloom
This preparation used the same brew ratio as the standard brew but bloomed the coffee with twice its weight in 195 °F water for 60 sec and then added the remaining water using room-temperature water. This method starts with an initial extraction of around 18% and climbs to its max extraction of about 21% over 8 hrs when steeped in the fridge. This early use of hot water pushes the initial extraction almost to final strength but still requires hours of steeping in order to achieve full extraction. This method tends to impart a sweet, tea-like taste to the coffee and the body is a bit thinner. Coffees with a higher presence of acidity may benefit from this method as it can promote a balanced cup with more acidity that doesn't overwhelm.
Austin Patterson with thoughts on extraction