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.

Temperature Experiments

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.

Ice-Cold Immersion

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.

Room-Temperature Immersion

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.