Batch Brewing Better
Let’s talk batch brewing. But first, let’s begin with our extraction paradox.
Generally speaking, finer ground particles of coffee have a larger surface area than coarser ground particles. The larger the surface area, the more efficiently the entire sample extracts. Efficiency, in this example, refers to more effective extraction over less time.
Let’s return to our extraction paradox. When we grind finely…
surface area and extraction efficiency increases
flow rate slows down
grounds spend more time in water between water distributions
and the elapsed time of water/coffee contact is longer
In a gravity driven brewing method like a pour over or a batch brew, we risk over-developing flavor (or extract too much flavor) on a pre-programmed timeline - resulting in a dry or unpleasantly bitter flavor. Like with most overcooking the result leaves little to no sweetness in the cup and the palate experience is a singular, unpleasant flavor.
Inversely, when we grind coarsely…
surface area and possible extraction efficiency decreases
flow rate speeds up
coffee grounds cool more between water distributions
the elapsed time of water/coffee contact shortens
In that same brewer, we risk under-developing flavor (or extracting too little flavor) on a pre-programmed timeline - resulting in an overly acidic, or overly-raw flavor. We miss opportunity for extraction and potential sweetness. Analogously, like an undercooked meal, we leave a lot of potential flavor development on the table and miss opportunity to present a complete cup.
The overlap in our Venn diagram above is a paired grind size (surface area) with flow rate. And again, we ask, what is our end goal? Here are a few examples of brewing goals:
Need 4 Speed = high extraction percentage in less time.
PRO: This model prioritizes grinding as finely as possible and extracting on a shorter timeline in order to get as much flavor out as fast as possible.
CON: Like shooting at a small, moving target, this model can has a small window for success but can taste amazing. When too much flavor is extracted, it can also leave the cup flavor muddled, the mouthfeel dry, and the origin of the coffee may be indiscernible.
ACTION ITEMS: increase the number of pulses (water distribution), decrease the volume of water per pulse, and shorten the elapsed time of water distributions. Oh, and grind finer than you normally would.
Darker Roasts need longer bloom time so put longer space between first and second pulse.
Lighter Roasts need less bloom time but do benefit from a tapered model. Consider increasing the water volume in early pulses and decreasing water volume over time.
Low & Slow = high extraction efficiency paced out over a longer timeline.
NOTE: This is a running debate in smart coffee circles right now. Most of us agree about prioritizing higher percentages of extraction (efficiency). Many of us disagree about how exactly you get there. This whole debate hinges on the margins - time, temperature, pressure, water quality, desired flavor outcomes. I’m going to skip that for now and talk through batch brew applications.
PRO: This model prioritizes grinding as coarsely as possible and extracting on a longer timeline in order to develop flavor slowly.
CON: Big targets aren’t as exciting to hit. The flavor cultivated on this model often lacks the precision of its faster sibling but it tends to exhibit developmental flavors that taste like the Enzymatic section of Ted Lingle’s flavor wheel. When not enough flavor is extracted here, the mouthfeel tends to be crisp, the flavor tart, and the developed sweetness of the roast may not be showcased.
ACTION ITEMS: Decrease the number of pulses (water distribution), increase the volume of water per pulse, and elongate the elapsed time of water distributions. Oh, and grind coarser than you normally would.
Darker Roasts’ lack of bean density mean that you may taste the roast more in this model. Try not elongating elapsed time as long as you would a lighter roast.
Lighter Roasts still benefit from a roller coaster model - but try reversing the taper. Consider using less lower water volume in early and later pulses and decreasing water volume over time.
In the above example, let’s assume that the same amount of the same water at the same temperature is distributed over same weight of coffees on the same timeline. The brew on the left (coarser) will very likely exhibit a lower percentage extraction than the right (finer) because it has both lower surface area and also the coarser grinds don’t restrict the flow rate of water - therefore the water and coffee will be in contact for less time.
The same but different: the brew on the right (finer) will very likely exhibit a higher percentage extraction than the left (coarser) because it has both higher surface area and also the finer grinds restrict flow rate of water - therefore water and coffee will be in contact for more time.
There’s an x factor of water retention that is correlated with grind size (which would affect yield and flavor) but we’ll save that for another day.
In the above model, we can easily recognize the efficiencies and inefficiencies of the two grind sizes, but we haven’t begun to talk about the flavor.
Flavor wise, we expect the right brewer to be further along the following spectrum than the left. How far along that spectrum depends on the ingredients, programming, water, age and origin of coffee used, etc.
In summary, if the goal is a balanced cup, we can easily program our brewers to a refractable optimum. If the goal is stylized, memorable coffees, we need to hack the final cup with a brewing strategy that makes sense for our specific coffee, water, tech, and flavor goals.