Memphis Coffee Expo - A Quick Review of Our Talking Points
this is a podcast episode, too! listen here :)
The Sustain team had the privilege of having a booth Grind City Coffee expo, right here in Memphis. If you are unfamiliar with what this expo is, let us fill you in!
The grind city coffee expo was first held in 2019, pre-pandemic. Despite some back-end hiccups, the event went well and there were plans to host another one in 2020. As one could assume, the 2020 expo was canceled in response to national health concerns. This year the expo is back on, and the Sustain Coffee crew will be there. The expo is geared around uniting the Memphis coffee community by having many of the key players under one roof - be those cafes, educators like us, roasters, and really anyone else who has a hand in our industry. The expo is unlike other expos because the proceeds benefit something huge - the Memphis Aquifer, more specifically, Protect Our Aquifer. “Protect Our Aquifer'' is a501(c)(3) nonprofit with a force of citizen advocates challenging threats to the Aquifer. In four years, POA has become a leading voice in the science-based protection of the Aquifer and the people that depend on it. The organization serves as a critical tool to unify the diverse stakeholders of water management to Protect Our Aquifer.”
———
As we know, quality water is vital for coffee brewing, and Memphis has the special advantage of having excellent tap water. In light of these things, we have decided to highlight some of our talking points that we covered at our booth.
Sweet, bitter, astringent… These are some of the taste descriptors we strive to balance when brewing coffee. But there are many other descriptors...sour, mouth-drying, juicy, sharp, soft, roast-y, delicate, floral, the list goes on.
These are just a few of the words we find ourselves using when talking about the taste of a said coffee. Perhaps we understand over and under extraction and the descriptors that match each of them, but do not exactly know why it is that way. We have been taught that variables such as grind, and time are huge contributors to taste (which they are) but how can we observe this scientifically?
For the expo we will have coffee that is split into three samples, each with only a singular variable that has been changed. This changed variable will be grind size.
Each sample will be verified using a refractometer to measure the TDS, and further calculated to determine EY. The purpose of this is to demonstrate just how impactful changing a variable can be, as well as putting numerical representation to our aforementioned taste descriptors.
We have chosen to utilize cold brew for the sake of time efficiency, otherwise we would be needing to brew quite a lot - as well as waiting for the samples to reach room temp. If you are unable to attend the expo, don’t worry, we plan on posting all of our results on Instagram.
We can observe the coffee brewing control chart for our references.
The chart is a relatively simple graph. TDS on the vertical axis, the EY or Percentage Extraction on the horizontal axis, and the brew ratio as diagonal lines. The chart is then split into nine primary boxes with appropriate sensory descriptive attributes. On the left we find low extraction we have “under-developed” flavors (sour, grassy, etc.) to the right at high extraction we have “bitter” flavors, and vertically we have the modifiers “strong” or “weak” at high or low TDS values respectively. In the center of the chart, we find IDEAL and optimally balanced.
The control chart has been around for decades, and was published in 1957 by the biochemist Ernest Earl Lockhart. This said, the control chart is still relevant, but its age gives way for improvement, and there are some exciting new developments on it.
———
Some notes on waste and why to measure TDS:
Is the refractometer needed to brew good coffee? Absolutely not.
Is the refractometer useful in understanding what is impacting the taste of the brew? A resounding yes.
The alternative to using a tool such as a refractometer would be to let taste be the only guide. Let’s say that one has a blanket recipe that has been created. Assuming that a pour-over dripper was being used, the recipe would contain starting points for: grind size, water temperature, dosage, coffee:water ratio, and pouring intervals. With the blanket recipe, one would brew the coffee, taste, reflect, and adjust as needed. This method is effective because it allows taste to be the ultimate guide and gives room for intuition from the individual brewing. Yet, it causes some subjectivity to be introduced. To combat this, one may ask peers or other knowledgeable people to give their feedback on a said cup’s taste. Yet again, there is still a lack of solidification of why a said cup tastes the way that it does. Thus we are forced to brew repeatedly, adjusting things as we intuit - and this is somewhat positive, as it gives us a chance to become better brewers. However, sometimes it is not merely the brewer, but the product being brewed. We see the negative in this repetition in two “wasted” areas: time and coffee. If the blanket recipe uses 20 < grams of coffee, and we have to brew upwards of five times, we have used 100g of coffee. This is a third of a normal retail bag. This may seem minimum, but is there not great merit found in pushing the minimum back even further?
Exceptions to TDS readings:
As a piece of technology, refractometer readings are subject to reading differently depending on a given situation. When a sample cools on the refractometer lens, we call this a form of stabilization. Over the course of the stabilization, the TDS reading will change.
Was the refractometer zeroed? Was it zeroed with the appropriate water/substance? Was the temperature of the zeroed sample different from that of the coffee sample?
The TDS is reading high, but this coffee tastes sour? The TDS reading is low, but this coffee does not taste under extracted?
Was there some arithmetic left out somewhere along the way?
Recall three things:
Coffee is a dynamic organic product, subject to differing topographies, chemical changes, and roast developments (all before it is ever brewed)
Taste can be seen mostly subjective (but there are objective perspectives, too)
Refractometers are merely a tool and readings should not be considered absolute
Some notes on Memphis water and water itself:
This will be the first time that we have ever truly addressed the topic of water. Let us explain why that is the case. Many of us on the Sustain team have let the topic of water quality go untouched, but it is not without reason.
Firstly, we recognize that water itself is a privilege, let alone clean, high-quality water.
Coffee comes from regions of the world where there are many people hurting for water, so who are we to measure the quality of our drinking water? It is important to keep these things in mind when discussing water quality.
Secondly, we do not want to let water preferences hinder our perspectives about certain regions of coffee.
We do not want to let water quality depreciate how we enjoy coffee, as it is a product that still deserves to be honored.
Yes, brewed coffee is mostly water.
Yes, the compounds found in water are important to take into account when brewing coffee.
Yes, observing water from a scientific perspective allows us to better understand taste and how coffee is broken down.
Just keep in mind that if we are even able to think about these “yes” things, then it means we are likely in a place of privilege.
We hope these clarifications are not too abstract but felt it necessary to acknowledge. Let these thoughts maintain our perspectives.
———
TDS readings are much like the scientific principles of diffusion, where compounds travel across areas of high and low concentrations. In terms of water and extraction, think efficiency.
This means that water with low mineral content is prone to over-extraction in coffee brewing.
This means that water with high mineral content is prone to under-extraction in coffee brewing.
The SCAA has landed on a recommended range of 75-250 mg/L for dissolved-solid concentration in water itself, with 150 mg/L being the ideal concentration.
According to studies, the water in the Memphis aquifer has a dissolved concentration of 100 mg/L and a pH of 7, generally speaking. In addition to these studies, Memphis water has low levels of fluoride, nitrate, lead, and copper and groundwater in the Memphis aquifer is a calcium-magnesium-sodium bicarbonate type.
Science aside, these things place Memphis water right in the neutral zone on the pH scale.
We know that a refractometer reads TDS of a coffee sample, but what is that TDS measurement composed of?
Dissolved solids of coffee include: chlorogenic acids, esters, and caffeine. Organic acids are present as well, such as: citric acid, malic acid, and lactic acid.
All of these compounds are what determines body, aroma, and flavor. Furthermore, when we are brewing coffee, we are constantly altering exactly how many of these compounds we are dissolving.
We know that brewing coffee is all about messing with variables and tweaking things to make the best cup possible. What alteration has the most impact on the compounds we are dissolving? We find that grind size and its relation to time affects TDS and in turn, EY % greatly.