9. Just say no: to pulse brewing

There has been much excitement this week in the Cincinnati coffee world. Thursday night, Deeper Roots is kicking off the release of their fall blend with a pour-over competition titled, “Taste is King.” Needless to say, I am pumped to be competing, but a few of us at Carabello Coffee have been debating the timeless question, to pulse pour or to continuously pour?

Pulse pouring is where the barista fills the (insert pour over method here) with hot water and lets it drain then adds more water and lets that drain. Hence, they are “pulsing” the water into the pour over. I believe this method is used for two reasons. First, to correct for inappropriate grind size. If the grind is too large, the water will pass through the pour over to quickly and not achieve sufficient extraction. Pulsing allows the water to soak in the coffee longer before being pushed through the filter by the next pulse. Second, the barista is a killer multi-tasker. They’re pulsing pour overs, pulling shots, steaming milk, and taking names. Pulse pouring allows you to divert your attention away from the pour over for a few seconds while the water drains. Whereas, continuous pouring requires the barista to sit there and stare at the pour over while getting a cramp in their shoulder from holding the kettle full of water at an awkward position. My opinion, stay away from pulse pouring and here’s why (from a hydraulic perspective, MATH AHEAD! but also cool drawings).

We’ve all been there, the lemonade stream has reduced to a trickle while we were pouring ourselves a cup from the five gallon drink dispenser. We’re trying to tip it forward while holding our cup and stabilizing the dispenser with our forehead so as to extract the last bit of goodness from the bottom of the barrel. By shear chance, the caterer (normally a mother if at a family picnic) observes your plight and fills up the dispenser. We’re saved! The lemonade comes gushing out and we’re off to the next event with some liquid refreshment. What happened here? We all know that when the dispenser is full, the lemonade comes out the quickest and that as it becomes more empty, the lemonade comes out slower. The speed at which the lemonade comes out of the dispenser is known as flow rate and is typically denoted by Q in the engineering world. What you’re observing with the drink dispenser is a type of orifice flow. The nozzle on the drink dispenser allows water to pass through it and into your cup. The flow rate (Q) in orifice flow is dependent on the hydraulic head (h). In general, hydraulic head is a fancy phrase for the height of a water or lemonade column above a certain reference point. This is similar to being in a pool and swimming to the bottom. When at the bottom of a 10 foot pool, you have 10 feet of water pushing down on you. This would be roughly equivalent to 10 feet of hydraulic head. The relationship between Q and h is that as h increases, Q also increases. So, the higher the lemonade column pushing down, the faster the lemonade comes out. We’ve all observed this reality. How does this translate to pour overs?

Take a look at this crude iPad drawing (I’m an engineer, not an artist, except for latte art) involving the typical pour over setup.

IMG_1156.PNG
We see that h is now the height of the liquid coffee in the pour over. This situation is not mathematically exactly the same as the lemonade example, but it’s similar. Realizing that a higher h means a faster Q, we can now deduce why pulsing the water into the pour over could lead to uneven coffee extraction. As the barista fills up the pour over, h increases and so does Q, but as the water drains h is decreasing and Q likewise. This leads to a roller coaster experience for our friend, Q. This causes water to be in contact with the coffee longer as h drops, which can lead to over extraction. Conversely, the water at the beginning of the pulse has less contact with the coffee as it is being pushed out and through the filter much quicker than the water above it, also leading to uneven extraction.

The moral of the story? By doing a continuous pour, h remains the same until the end. This allows our friend, Q to stay the same as well (for the most part, I’m not going to discuss the changing density of the coffee bed due to migration of fine particles). Since great coffee extraction is about consistency, doesn’t it make sense to pour in a way that provides a consistent flow rate?

Just say no to pulse brewing.

And RIDE THE BLOOM! (a shoutout for Malcolm and Jacoby of Carabello Coffee)


3 thoughts on “9. Just say no: to pulse brewing

  1. Will,
    Thanks for posting this. I have noticed a difference in the pulse/continuous pour-over methods. Even in my childproof (read: inexpensive) Mellita pour over we purchased, we can get a much better cup when we simply pour slower vs. the pulsing you wrote about. I believe this is what you were referring to. Thanks for putting some thought, math and pictures to it. Everything is better with math and pictures. 🙂

  2. This is true. I would be interested to test this by adding even another variable. Imagine doing a pour for a 12 oz cup. If 12oz of water were poured continuously (NOT PULSED), would there not still be two intervals of time (one near the beginning and one near the end of the pour) during which the extraction would be “rollercoastering?” In other words, at the beginning and end of the pour, when h is below the target level for the continuous pour, q will not be consistent.
    So, a thought arises: let’s say we want to brew the same 12 fl oz cup. However, this time use a high enough dose of coffee and water for a 14 fl oz cup. Let’s assume that 1 oz of water will need to flow through the coffee before h is at our target level, and another oz will be left to drain through the grounds when the pour is over. Now, imagine we have a way to keep that initial oz and final oz separated from the 12 oz that were brewed when when h was at our target level 100% of the time. Would that yield the most consistent and even extraction possible? I don’t know. But I’d say let’s try it.

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