How to Make Tasty Commercial Cold Brew Using TDS and Extraction Percentage
Cold Brew Simplified | Learn more about the ACE Brewer here
Written by Ray Burger – Brew Bomb
Using Objective Data for optimizing Taste and Yield
Breaking down cold brewing into the objective measurements of TDS and an Extraction Percentage will point you in the right direction for optimizing both the flavor and yield of your commercial cold brew.
is how much of the dry ground coffee is moved from the ground bed into the brew. Measuring how much of the ground coffee was displaced into the brew is called the Extraction Percent. For example, if you are brewing with 10 lbs of ground coffee and your Extraction Percent is 20%, this means that 2 lbs, (20% of 10 lbs) was actually extracted from the dry coffee and is now in your cold brew yield. Following the example further would be to determine the concentration of the brew. If the 2 lbs of extracted coffee compounds are in 3.4 gallons of water the concentration is greater than if the 2 lbs of coffee compounds are in 6.0 gallons of water. This concentration is measured as Total Dissolved Solids or TDS.
The key to tasty brew
is to balance the cup notes inherent in your origin/roast. If the flavor of the brew at the beginning of the extraction process is sour, adding the bitter notes that extract at the end will balance the cup experience. This is how using Percent Extraction can bring objective data to the process. A balanced cold brew cup is typically produced when the Extraction Percent is in the 17- 20 range. This optimal range is lower than coffee brewed with hot water.
HOW DO I CALCULATE PERCENT EXTRACTION?
To determine how much coffee was displaced from the ground bed into the brew, start by using a refractometer to measure the concentration or TDS. TDS is the percentage of coffee compounds in the brew. A reading of 4.0 TDS for example, means that for the fluid being tested, 4% is coffee compounds* and the other 96% is water.
Armed with the TDS, the actual weight of the coffee extracted into the brew can be calculated by taking the weight of the brew multiplied by the TDS percentage. The imperial system adds a layer of complexity because a gallon is volume not weight. Since 1 gallon of water weighs 8.35 lbs, first convert the brewed yield to weight by multiplying the yield times 8.35. Using the example from above, if the yield is 6.0 gallons the total weight of the brew is, 6 x 8.35 = 50.1 lbs. If the TDS is 4.0 this means that 4% of the 50.1 lbs is coffee compounds. 50.1 lbs x .04 = 2 lbs. This brew extracted 2 lbs of coffee from the original 10 lbs for a Extraction Percent of 20%. (2/10)=.2
This objective data point is at the upper end of the optimal range which suggests that the yield is maximized and the cup quality is acceptable. If the cup is overly bitter then simply adjust the next brew so that the target Percent Extraction is lower, perhaps in the 18-19% range.
*the compounds measured with a refractometer will include calcium and magnesium as well as other solids contained within the water itself.
USE THIS GUIDE TO ADJUST BREWING VARIABLES
We strongly recommend changing only 1 variable at a time otherwise you will never have a direct cause and effect relationship.
Extraction percent less than optimal
- Increase the brew yield.
- Grind the coffee finer
- Over extracted coffee can be bitter, chalky or astringent
Extraction Percent greater than optimal.
- Decrease the brew yield
- Grind the coffee courser
- Under extracted coffee can be sour.