Blend Probability
A word from our education director, Trevor Clark
September 2024
As decadent as a birthday celebration should be, each batch of The House That Gesha Built contains a staggering 10 lots of Gesha variety coffee. If that seems absurd—good. It is absurd!
When we first announced this release, we received a great question on Instagram: with so many coffees, isn’t it possible that a dose of this coffee could exclude one or two components?
Our answer: it certainly is possible. It’s extremely likely!
The House That Gesha Built is a gleeful celebration of phenomenal coffee, and we believe that any constellation of these stellar Geshas results in a memorable cup. And according to the rules of probability, it’s likely that no two brews will be quite the same.
While The House That Gesha Built intentionally pushes this principle to its extreme, all blends present this same statistical dilemma, where the actual mix of coffee may vary between shots of espresso or pour-over doses.
Compound event probability helps us understand the odds of our coffee dose reflecting the overall blend composition. The formula is simple: convert the percentage of all blend components to decimals, then multiply all decimals to determine the odds.
For example, let’s consider a reasonably uncomplicated blend with three components: Coffee A is 50%, Coffee B is 30%, and Coffee C is the remaining 20% of the mix. Multiply 0.5 by 0.3 by 0.2 and you get .03, or a 3% chance of a random sample showcasing the true blend recipe.
Now let’s imagine you’re using this blend for espresso, dosing 18 grams of coffee for every shot. With a 3% chance of finding the true blend recipe in your portafilter, you’re only going to dose the true blend once per every 1.3 pounds of coffee used.
This assumes that all coffee gets a fair shot of ending up in the portafilter, too. We’re not considering how each coffee seed’s shape and size will cause layering in a bag or in a grinder hopper. And we’re not accounting for each bag being dosed from a much larger batch of blended coffee, further cutting into the probability of a “true blend” in every cup.
Feeling discouraged by brewing blends? Don’t be! This is the part where statistics take a backseat to raw human experience and the power of tasting.
Just because a dose of coffee doesn’t perfectly match the roaster’s blend doesn’t mean it won’t convey the intended flavors. A single coffee seed can transform a cup’s profile, meaning that a very small appearance by a blend component can ensure the conveyance of specific flavors.
Roasters also cup their coffees constantly to ensure their intended flavor profile displays in each batch of coffee. At Black & White, we’re evaluating our blends every roast day, assessing the overarching consistency of flavors in each cup of coffee.
If you’re looking to eliminate blend variation, you can dose out your own blends, combining specific lots of coffee in each dose and grinding through the entire sort. It’s common to see this technique in competition settings, adding an extra layer of assurance that specific flavors convey. This process would be too time-consuming for a busy cafe dosing espresso, but it can provide a workaround for those pursuing a higher degree of control in their coffee’s profile.
It’s worth considering that most “single origin” coffees can be blends in their own way. Harvesting from multiple trees, potentially of different varieties, with varied elevation and irrigation can produce an array of results. The coffee may be harvested and processed on different days, creating different climatic conditions for the final coffee. While most specialty lots will provide a consistent flavor profile, it’s worth considering the ways that these coffees are also composites of many parts.
Whether billed as a blend or a single origin, we encourage you to let taste guide the way for your coffee selection. Forget the components and the compound event probability: close your eyes, take a sip, and remember: if it tastes good, it is good.
