undissolved solids

How important is the “bloom” in a pourover?

Lately I’ve been experimenting, reading and watching random bits and bobs around changing singular variables around the “bloom” of a pourover. I have mostly been using longer bloom times to push extraction% for certain coffees that naturally have higher perceived acidity (i.e. washed Kenyans) just to balance them out a bit.

Here I wanted to discuss mostly what I have found over these tests and resources.

No TLDR – scroll to the end if you don’t wanna read the context 🙂

In pourovers, the “bloom” is the phase at the start of the extraction when hot water hits the dry bed of coffee and CO2 is released from the grounds (visually shown by bubbles forming at the surface of the [wet] coffee grounds. Over time as coffee ages, the amount of bubbles produced in this phase will decrease (as coffee degasses). But is there more to this phase than just pouring at a 1:2 or 1:3 ratio for 30 seconds? Let’s explore this.

I have come across multiple sources discussing the different theories around bloom variables such as volume, time and temp.

Reference 1: Jonathan Gagne (The physics of filter coffee, chapter 1)

  • Advection: Washing/transporting of surfaced soluble coffee particles (via water) downstream into the caraffe/cup
  • Pushing extraction via advection can be by more agitation (high pouring / circular pours / stirring / swirling)
  • Diffusion: Sort of osmosis-type system that transfer particles from highly-concentrated coffee particle to the low-concentrate freshly introduced water (in absence of flow)
  • Pushing extraction via diffusion can be by increasing temperature of the kettle water or waiting longer between pours (or in immersion-style brews, letting coffee grounds sit in the water for longer)
  • In absence of flow, diffusion becomes superior in the extraction meaning that a longer bloom waiting time allows more diffusion to occur = higher availability of soluble particles at the surface of the grounds to be advected
  • During a bloom, usually advection dominates the majority of the earlier extraction as you try wet the whole bed of coffee. Diffusion does start BUT mostly the lighter, volatile compounds will come out first and the slower, organic bitter acids will come out a bit later

Reference 2: Lance Hedrick pourover philosophy

  • He typically uses longer bloom times (up to 2 mins) to push extraction in his coffees.
  • This is usually used for denser (typically) washed coffees that tend to run fast and extract on the lower-end using his normal recipe)
  • In a video (https://www.youtube.com/watch?v=eVF7DOxOUFA&ab_channel=LanceHedrick) he discusses trying a cold bloom (named “samo-bloom”) @50-60C to capture more volatile aromatic oils in a less reactive/volatile environment (due to cooler water) as they are easily soluble → similar concept to compound chilling

Reference 3: April coffee (https://www.youtube.com/watch?v=VheCmEzDfvs&ab_channel=CoffeewithApril)

  • found that longer bloom times increase extraction overall

Reference 4: Tetsu method

  • More water in bloom = more acidity in the overall cup due to lower volume water available in subsequent pour
  • Less water in the bloom = more sweetness(body) in the cup due to higher volume in the subsequent pour

Reference 5: Recent Lance Hedrick video (https://www.youtube.com/watch?v=0pEja0GHWuU&ab_channel=LanceHedrick)

  • bitter organic acids diffuse out of the coffee a lot slower due to their weight
    • my note: this means higher temperatures would speeden the outward diffusion of organic acids into the water as volatile oils are more easily soluble (at quite low temp) = higher temp = higher body

SO WHAT DOES THIS MEAN?

Let’s firstly assume that all other variables in the pourover procedure are set as well as “bypass” (water finding the lowest path of resistance and advecting minimal coffee). So now, let’s look even further into the big three variables in the bloom that have popped up in these sources and see how these variables do end up changing the cup.

Volume of bloom

↑ Bloom volume/weight = ↑ water available to extract early coffee compounds (higher volatile oils extracted)

  • result = ↑ perceived acidity in the brew also can be due to less water being used in the subsequent pour

↓ Bloom volume/weight = less water to extract early compounds

  • result = ↑ body/sweetness attributed to more water being available to advect the slower-diffusing compounds (i.e. heavier organic acids)

Bloom time

↑ bloom time = ↑ quantity of organic acids (heavy bitter compounds) available to be advected in next pour

  • result = ↑ extraction%

↓ bloom time = ↓ quantity of organic acids available in next pour

  • result = more prominent perceived acidity due to reduced organic acids & ↓ extraction%

Bloom Temperature

↑ Bloom temperature = ↑ rate of reactions occurring = ↑ volatile compounds and some organic acids

  • result = leaning more to balanced brew & possibly ↓ in aromatic compounds released in the air

↓ Bloom temperature = ↓ rate of reactions occurring BUT volatile acids are quite soluble even at lower temp = ↓ reactive/volatile environment = ↓ volatile aromatic compounds released in the air

  • result = ↑ perceived acidity (possibly more aroma – similar to paragon extract chilling)

Thanks for reading,

jos x