One of the most frequently misunderstood accounting problems in coffee roasting is the loss of mass during the roasting process.
Green coffee goes in, roasted coffee comes out, and there’s magically less of it. Even at small scales, improperly calculating your roast yields can cause major inventory and financial headaches, so it’s worth knowing exactly what to account for, and how to do it quickly and easily.
- Weigh every batch before and after roasting
- Roast Loss/Yield are two sides of the same coin
- Yield/Loss are determined by roast degree, green coffee moisture, and qc protocols
How To Calculate Roast Yield and Loss
Let’s say you’re operating a machine with a 100-pound capacity. A full batch of green coffee goes in at 100 pounds and weighs roughly 85 pounds once it’s finished. 85 pounds is the roast yield, while 15 pounds (or 15%) in the loss.
There are three main factors to consider when attempting to calculate roast loss:
Degree of Roast
Roast degree, your combined end values of roast time, temperature, color, etc., is likely the most significant factor in how much product is lost during the process.
Darker roasts lose more weight than lighter roasts. Very light roasts, dropped at the beginning of the first crack, will likely lose only about 10% of their green weight, but roasts taken well past the second crack may lose as much as 25%.
Establishing benchmarks for different roast degrees will be important to the way you calculate your green and roasted inventory. By using batch weights, green in and roasted out, for every coffee, you’ll be able to confirm similar roast degrees by similar end weights, and quickly identify if someone made a measurable error in green batch size (if you get 85 pounds out of an 80-pound green batch, something’s obviously not right)
An added benefit: comparing roasted output weights of different roast levels can potentially offer roasteries an inexpensive (albeit imperfect) alternative to color meters.
Most importantly, it will help you calculate backward when determining your daily green batch weights, as well as projecting for overall purchase volumes.
For example, let’s say your roast order includes 1000 one-pound orders for your light roast Kenya, 1000 orders for your medium roast Brazil, and 1000 orders for your dark roast Sumatra. Your Kenya loses about 12%, your Brazil about 15%, and your Sumatra roughly 20%, making the roast yields 88%, 85%, and 80% respectively. Now your green coffee input for the day becomes an easy calculation:
Knowing your roast yield for any given coffee saves you the guesswork of deciding on your batch size and should help prevent that awkward moment when you’ve shut off your machine, bagged up your last beans but still have twenty more orders to fill before UPS comes by for a pickup.
Green Coffee Moisture Content
The moisture content of most coffee prior to export is set at around 10-12%. While this small variance may not seem like much, it can definitely be observed in the way coffee roasts, ages, and even tastes. Some coffee falls outside of these boundaries, making the impact of total moisture content to a roaster a very important measurement to monitor.
Moisture content impacts roast yield directly, as well. All of the moisture in a green coffee will burn off during roasting, making a baseline, theoretical formula for determining your output: Moisture + Roast Degree = Roast Loss
For example, let’s say we’re sample roasting a few coffees to purchase. If all coffee is roasted in the same style to a very light degree where the only weight lost is water weight, three samples of varying moisture will have different weights after roasting even if the roast degree is the same.
Incidentally, because coffee is bought and sold by weight, both before and after roasting, it’s often in a roaster’s best interest to look for lower moisture coffees, as your percent of product loss is lower.
In the example above, if a roaster bought ten 132-lb (60-kg) bags each of Kenya and the Sumatra, and if both coffees cost $5 per pound (green), the total value of each coffee would be $6,600. If the coffee was then roasted in the same style (let’s say to the medium roast % above), the total roast weight difference between the two coffees – due to moisture content alone – is more than 50lbs. The total value of coffee lost due to moisture weight alone would be 4% more for Sumatra. The roaster would be left with the following:
Even though the green weight and cost of raw goods are the same, at the end of roasting you’re left with 4% less product on the higher moisture content Sumatra, in this case, valued at $264 less than the dryer Kenya.
If these coffees both retail for $20/lb on the shelf, the difference is even greater. With 52.8 more pounds to sell of the Kenya, by the time you’ve sold all the coffee, it results in a gross profit of over $1000 greater than the Sumatra (Notably, we’re ignoring some factors for the sake of convenience, such as labor, energy, packaging, and shipping).
Lastly, a roast yield may be impacted by coffee used for purposes of quality control. Production roasts are frequently cupped and color analyzed to confirm adherence to in-house standards. You’ll want to make sure you account for any coffee needed for these purposes, so you don’t end up shorting your customers because you needed some of their coffee to perform quality checks.
For our QC purposes, we Colortrack every roast. Ground coffee to fill the Colortrack tray takes about 100g. We have four cuppers, and we currently do not share cups, so each cupper needs 10.5g times two cups plus a purge cup, or about another 100 grams, give or take. The QC “Angels’ Share” is roughly 200g per batch, a little less than half a pound.
In a small 5-lb batch on our Diedrich, the roast yield might be 13% or 4.35 lbs. Subtract another half pound from that, you get 3.85 pounds, or a 23% loss total from green to roasted. 10% of this coffee went to QC. If we needed 4lbs roasted, we would have to tighten our belts a little — re-use the Colortrack coffee for cupping, for example, or just batch up another half-pound or so to make up the difference.
At larger batch sizes, the impact of these QC practices is reduced: a full-size batch on the Loring of 33lbs might result in a similar roast loss, 13% or 28.71 roasted pounds. Losing another ½ pound to QC protocols yields a total final roasted weight of 28.21, or 14.5% loss. A relatively small difference, but one that should still be accounted for given that it could make the difference between 57 or 56 half-pound bags, if that were the use-case scenario in question, as an example.
Every good roaster should know the value of their product. That value necessarily changes based on the weight loss/yield after roasting. Understanding the factors that alter a coffee’s roast yield can help ease predictions for roast days, better manage profit margins, and prevent awkward mistakes.