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#85 | How to Maximize the Flavor Potential of Your Brewed Coffee | Expo Lectures 2019

#85 | How to Maximize the Flavor Potential of Your Brewed Coffee | Expo Lectures 2019

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The original brewing control chart is overlaid with acceptability zones describing cup flavors. However, these terminologies (strong, bitter, weak, over, and under-developed) are outdated and their definitions are not standardized in the industry. In this lecture, the newest results from the UC Davis Coffee Center will be presented, which used the WCR Sensory Lexicon in order to elucidate new flavor attributes related to coffees of different strengths and extractions. The experiment evaluated a single origin coffee roasted to three different development times in order to assess the importance of roast on the flavor at different strengths and extractions. The position of the coffees on the brewing control chart was modified by using a programmable batch brewer. A descriptive analysis panel was used to capture the sensory profile of these coffees. The results presented will be used to update the descriptive zones of the new brewing control chart.

In today’s lecture by Dr. Scott Frost, you’ll learn all about how flavor can be modified through the brewing process, and how the control chart can be used to create different flavors for a specific coffee. 

Scott received his Master of Science in Viticulture and Enology and Ph.D. in Agricultural and Environmental Chemistry from the University of California, Davis. His graduate research focused on evaluating the sensory and chemical changes in wine as a result of specific enological practices. At the time of the recording, Scott worked at the UC Davis Coffee Center as a Postdoctoral Scholar. His project applies quantitative sensory methods to capture the sensory profile of brewed coffee.

Special Thanks to Softengine Coffee One, Powered by SAP 

This episode of the Expo 2019 Lectures podcast is supported by Softengine Coffee One, Powered by SAP.  Built upon SAP’s business-leading Enterprise Resource Planning solution, Softengine Coffee One is designed specifically to quickly and easily take your small-to-medium coffee company working at any point along the coffee chain to the next level of success. Learn more about Softengine Coffee One at softengine.com, with special pricing available for SCA Members. Softengine: the most intelligent way to grow your business.

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Episode Table of Contents

0:00 Introduction
3:20 The methodology and results of Scott Frost’s experiments
36:15 Audience questions
41:15 Outro

Full Episode Transcript

0:00 Introduction

Heather Ward: Hello everyone! I’m Heather Ward, the SCA’s Senior Director of Content Strategy, and you’re listening to the SCA Podcast. Today’s episode is part of our Expo Lecture Series, dedicated to showcasing a curated selection of the extensive live lectures offered at our Specialty Coffee Expo. Check out the show notes for relevant links and a full transcript of today’s lecture.

This episode of the Expo 2019 Lectures podcast is supported by Softengine Coffee One, Powered by SAP.  Built upon SAP’s business-leading Enterprise Resource Planning solution, Softengine Coffee One is designed to quickly and easily take your small-to-medium coffee company working at any point along the coffee chain to the next level of success. Learn more about Softengine Coffee One at softengine.com, with special pricing available for SCA Members. Softengine: the most intelligent way to grow your business.

The episode you’re about to hear was recorded live at the 2019 Specialty Coffee Expo in Boston. Don’t miss next year’s lecture series in Portland – find us on social media or sign up for our monthly newsletter to keep up-to-date with all our announcements, including ways to get involved in next year’s Expo and early-bird ticket release!

The original brewing control chart is overlaid with acceptability zones describing cup flavors. However, these terminologies (strong, bitter, weak, over, and under-developed) are outdated and their definitions are not standardized in the industry. In this lecture, the newest results from the UC Davis Coffee Center will be presented, which used the WCR Sensory Lexicon in order to elucidate new flavor attributes related to coffees of different strengths and extractions. The experiment evaluated a single origin coffee roasted to three different development times in order to assess the importance of roast on the flavor at different strengths and extractions. The position of the coffees on the brewing control chart was modified by using a programmable batch brewer. A descriptive analysis panel was used to capture the sensory profile of these coffees. The results presented will be used to update the descriptive zones of the new brewing control chart.

In today’s lecture by Dr. Scott Frost, you’ll learn all about how flavor can be modified through the brewing process, and how the control chart can be used to create different flavors for a specific coffee.

Scott received his Master of Science in Viticulture and Enology and Ph.D. in Agricultural and Environmental Chemistry from the University of California, Davis. His graduate research focused on evaluating the sensory and chemical changes in wine as a result of specific enological practices.

At the time of the recording, Scott worked at the UC Davis Coffee Center as a Postdoctoral Scholar. His project applies quantitative sensory methods to capture the sensory profile of brewed coffee.

This lecture has some very technical graphs that are difficult to describe. As Scott is getting ready to officially publish these results, we’re unable to share his visuals with you today, but we’ll be sure to let you know when some of these graphs are available for you see.

Okay, let’s dive in.

3:20 The methodology and results of Scott Frost’s experiments

Scott Frost: So when we talk about the Brewing Control Chart, I think, one of the best places to start is with the Coffee Brewing Institute. Established in 1952, this was a research body that was designed to encourage the industry to learn more about coffee and so the Director was this gentleman Earnest Lockhart., and he was quite prolific in coffee.

Lockhart has quite an interesting background. In the 1940s he went to Antarctica with General Byrd. He actually has a mountain named after him in Antartica. Later on in 1960 he went back to M.I.T. where he was a Biochemist and a Food Scientist and from there he joined the Coffee Brewing Institute. There was an excellent article by Emma Sage looking at the history and the setting up of the Coffee Brewing Institute.

Lockhart is known for this publication that came out in 1957.  The idea behind this publication was that he was attempting to create an index. A single number to describe the quality of coffee. This publication is the basis of how to brew coffee and the title was Soluble Solids in Beverage Quality or Beverage Coffee as an index of cup quality. So the first thing that he says in the abstract of this publication is that a quality or acceptability of coffee beverage or any other food is incredibly difficult to capture. That’s kind of a take-home message that a single number to ascertain quality is incredibly difficult.

Within this publication, they attempted to relate these three parameters, these three basic brewing fundamental parameters. The first being brewing formula, the ratio of water to coffee, the second being percent extraction, the amount of coffee removed from the coffee grounds inside the brew basket and then, total is all solids,  the strength of the actual beverage that you get out at the end.

This 1957 publication from Lockhart was the graphic that they produced showing brew formula along the X strength of coffees of TDS soluble solids, the Y, and then the lines are the instruction percentage.  I have highlighted here this box that they overlayed this ideal quality box. At the time there was some competing discussion over what the box was. This infamous coffee box that we have. There was two different boxes, one from the Brewing Committee and one from the Midwest Research Institute.

If you look at this plot, you can reorganize it or re-plot it. This is the one that we see in the coffee brewing handbook from the SCA.

Heather Ward: Scott is describing the Lockhart Brewing Control Chart. If you’re unfamiliar with the chart, check the show notes for a link to different versions of this chart. 

Scott Frost: which has extraction along the X strength up the Y and the lines are the dose.

And so they’ve also overlaid….The idea is that the pair between the extraction and the strength is the brew index. A 2% extraction TDS pair would be the brew index. They also overlayed on this chart, this verbiage, “developed”, “underdeveloped”, “strong” and “weak”. There’s also the stark lines between moving from underdeveloped to ideal to bitter. That gives an indication that you can very quickly move from being underdeveloped to this ideal cup of coffee instantaneously bypassing from, 18.8 and 19. So that’s a little bit constricted. Additionally, these words of developed and underdeveloped they’re preference words. So one person’s overdeveloped or underdeveloped coffee, maybe someone else’s perfect coffee.

We always question this ideal box, ideal says who? What I’m interested in is that coffee is so much more than just this developed, underdeveloped, bitter, et cetera. We have this beautiful lexicon that we use to describe coffee with this coffee wheel. You see it plastered all over this conference everywhere we go.

What I wanted to know and what we were curious about at Davis in conjunction with Rebel and the SCA, is how does this lexicon relate to the Brewing Control Chart? How do these words relate to index positions along the chart?

We set out to ask this question. How do specific sensory attributes change in respect to the Brewing Control Chart?  We partnered with Rebel and the SCA, and we tested this hypothesis. If coffee is brewed at a different index position, It’s perceived sensory will change. That’s the hypothesis for the experiment that I’ll be talking about today.

Heather Ward: Scott’s slide is titled ‘Experiment design’. It shows the nine types of brews he’s testing. These brews are combinations of TDS levels and extraction levels. Three types of TDS levels are: 1%, 1.25%,  and 1.5%. The three levels of extraction are 16%, 20%, and 24%.

Scott Frost:  I’m going to talk about the experiment that we did, the design of the experiment.  I have here a Brewing Control Chart with the lines removed with everything remove. I kept the boxes and the lines because that’s the basis of what we’re working with.

We wanted to test across the entire chart, so we set up an experiment looking at three levels of percent extraction 16, 20 and 24 and three levels of TDS. 1, 1.25 and 1.50. and we tested all nine combinations of these, TDS and extraction pairs. This was the basis of our experiment design.  We needed to up it just a little bit, so we included coffee as another factor within the experiment.

Heather Ward: Scott’s slide shares more information about the coffee used in the experiment. It was grown by Cooperativa de Horticultors Siguatepeque in Hondouras and is a mix of Bourbon, Catui, Caturra, and Pacas. The slide notes the altitude – 1300-1650 meters above sea level – and the processes are fully washed and sun-dried.

Scott Frost: We sourced a coffee from Honduras and Siguatepeque. The coffee was donated by Royal and the coffee was roasted by Blue Bottle by Juliet Han.  I have to take a second and tell you how I am a better coffee person having worked with both Jen and Juliette. I can’t thank them enough for the time that we got to spend with them.

Juliet roasted our coffee and we decided to use development time, so the time post crack as a way to make coffee treatments. We made arbitrary designations of the coffee as light, medium, and dark.

I put up the roasting curves up here so we can get an understanding of what we have. In our roast losses running from 14, 15 and 16% roasts loss for light, medium, dark.  So now we have 27 different coffees. We have a light roast, a medium roast, and a dark roast as designated by the development time.

Each of those coffees had nine coffees within it, so evaluating three levels of TDS, three levels of an extraction, every combination within giving, 27 different brews from the one single green coffee. So actually what we are trying to do, we’re trying to look at how has the brewing index changed?

Oh, this is a big part.  I need to take a quick detour here.  In order to move around the Brewing Control Chart, to effectively dial up the coffee that we wanted, we needed to learn how to brew in our lab, so we were using the Curtis G1. These one gallon batch brewers. We have six of them in our lab.

What we did is we programmed the brewers to pulse water on and off at a given rate at a cycle. We used this duty cycle, this pulsing on, pulsing off to change the TDS of the coffee to change the strength, changed the brew index of the coffee. So even before we could get to the Brewing Control Chart, we had to do a prequel experiment to this.

We did four brewing ratios of equal grind, all brewed at 95 or 9.5 C, 17 different pulsing sequences. Three brew replicates. We brew 204 pots of coffee before we even got to the descriptive analysis portion. What we found was that it was pretty intuitive, the longer the duty cycle.  The shorter the duty cycle.  So increasing duty cycle, increase extraction strength. So if we look up here at this one, that’s says 16.7 that’s way up here at this top end. So what that is, that’s very quick, That’s pulsing on and pulsing off, pulsing on and pulsing off pulsing on and pulsing off across the entire brew.

And down here, in these like pinkish bluish ones, this gets down to be closer to the 100% duty cycle, which is constant on. So using contact time and the link for the brew, we were able to brew across the chart. What that allowed us to do is effectively dial up a brew, just plug it in and go for it. So we use this principle to move around the chart, and this work is currently being written up, being worked on for publication at Davis.

So back to what we did. Using that pulsing, that duty cycle information to change our index position, we evaluated these 27 coffees across these three different roasts.

We were curious about the sensory properties of these 27 different coffees, and we used a method called descriptive analysis, which attempts to describe, quantitatively describe specific sensory attributes of a product set.  So description analysis is applied methodology to collect quantitative measures of similarities and differences within a product set. It’s trained judges. It’s concise within this lexicon requires an experimental design, and it needs controlled conditions.

I have here, that’s actually Juliet in my booth with the red light but we’ll talk more about that in a bit. So as mentioned previously, we have trained judges, a concise lexicon, an experimental design and controlled conditions.  The first thing we do with descriptive analysis is we convene a panel of judges and these judges were pre-screened using some triangle testing, some discrimination testing.

We wanted people who have a little bit of understanding of coffee before we bring them into our lab. The judges are blind, the products and the treatment. They were presented with the SCA/WCR wheel and asked to develop or come up with words that they’re perceiving in the coffees for this training.

So they developed this giant list of words this lexicon, of words that they can use to describe and discriminate the given coffees within the data set. They came up with this list of 32 different flavors, aroma and taste attributes.  So each one of those 32 tastes attributes comes with a reference standard.

The part that changes it from green preference to being quantitative and descriptive, is that there’s a reference standard behind it so that we can go and we can say, for example, for tobacco, everyone on the panel smells the tobacco and they say, yes that’s tobacco.

There’s no question that only this smells like, my grandma’s basement or something else. Everyone is keyed into the same aroma for the product set that you have.  We have 32 for this experiment.  Here they are, a giant lists from black pepper, cocoa, floral, smoke, nutty, black tea, blueberry, et cetera, dark green, Burnt wood, Ash, prune, raisin, et cetera.

So once we get the panel trained, we take them in and we put them in the booth, and this is a shot from sitting in the booth chair and you can see up there. Right there is a little door and we feed them in the trays of coffee, one coffee at a time, open the door, slide it in, and then they lay on this, what’s called an unstructured length scale right here.

Their perceived intensity of the coffee that they have. They received coffee one at a time.  We get one coffee, they would score all the attributes, put that coffee back out and get the next one.

So we have 12 judges, each judge tasted all coffees in triplicate for experimental replication for statistics.

Heather Ward: Scott’s slide is titled ‘measured strength and extraction’. There are three copies of the Strength against Extraction charts. Each chart is showing the results of a different coffee roast level. These are light, medium and dark roast. Within each chart are the coffees they brewed for the experiment which targeted specific TDS and Percent Extraction combinations.

Scott Frost:  For good sentence. Okay, so now. In order to capture all these coffees and allow all 12 panelists to taste all the coffees across the data collection period, each coffee needed nine different brews. When I say one coffee, I’m talking about, for example, light roast at 16% at 1.5 TDS, that’s one coffee.

So one coffee would be the roast extraction TDS pair. Each one of these represents nine different points. There’s nine here, there’s nine here, there’s nine here.  And I put this up there to demonstrate the number of coffees that we brewed for this experiment. So now  I’m at 243 brews, that’s 400 and almost 450 brews between this experiment and the pulsing experiment using these first batch brewers.

Also, this is raw TDS and raw percentage extraction data. I think it really shows well the reproducibility of our brewer and our reproducibility of our experiment.  So I’ll just pop one out for you so you can see. What I need to make very, very clear is that we were intending to brew to a tedious person extraction, and in order to do that, we kept the dosing water the same that’s about 3100 grams of water, but we modified the brew ratio, we modified the grind to be able to move about the chart. I make it clear that the intention was to hit a particular point on the chart and make that as our comparison. Those are the variables that we hold constant.

For example, for a 1.0 and 16, it was a very high duty cycle at 83%, so the brew was a very short time, it was a couple of minutes to brew 176 pounds of coffee into the basket of the brewer at a brew ratio of 17.5. This is the median, the median particle size of the grind, and so forth.

Over here, for example, at 1.25 and 24, which was this particular position on the chart required a duty cycle of 20% so a much longer, longer brew. This brew was in the ballpark of 15 to 20 minutes, 150 grams of coffee a brew ratio of 20.6 to one and a much smaller particle size.

We did descriptive analysis across those 27 coffees. All 12 of our judges tasted each coffee in triplicate and they scored using that line scale. So this is what raw descriptive analysis data looks like, it is this giant table of rows and columns and you end up with your judges down the side. This column is a… the judge column, and then the individual coffee, then the aromas across the top.

From there we did analysis of various attributes to determine which attributes are significantly different for a single coffee. One of the best ways that we can quickly, display the results of this data is something called Principal Component Analysis. This relates the rows and columns together. It allows you to make determinations between an individual coffee and an attribute. So this also allows us to see how our experiment laid out, whether or not the treatments make sense within the space of the collected data. So the PCA was really clean for this one.

Heather Ward: Scott’s slide is titled “Principal Component Analysis.” It shows a scattering of data points along the two axes – the X axis is labeled ‘principal component 1 of fifty-nine point five percent’ and while the Y axis is labeled ‘principal component 2 of twenty-three point nine percent.’

Scott Frost:  I’m going to back up for a second. One particular thing, and I hope to see more of this type of analysis in the coffee industry as you guys move forward.

It’s very important to see on the PCA. The first thing, you look at the two dimensions that are displayed in the PCA. This one is accounting for 59.5% of the variability within the data table presented within this X, Y space. So what we’ll usually do in the sensory world or when you use this Principle Component Analysis, is you add this up, so about 60% and about 23 so 63% of the variability within the data is captured within this graphic on the screen and we can also make an assumption, we can see that the sample separate by the factors of the experiment. We can see the dark roast is off to the right, the medium roast runs through the middle, and the light roast runs over her on the left-hand side. Let me back that up for you guys and see. Each of these points is indicated by the coffee.

For example, we have D 1.25 and 24 so dark roast, we were at 1.25 in 24% extraction. As I said, the dark roast coffees we’re positioned to the right, medium roast coffees we’re positioned in the middle and the light roast coffees were positioned to the left-hand side. So roast separates along the first component, meaning that roast is a very important factor.

The next thing that we want to look at, the factor was TDS, the strength of the coffee, separating or flogging off the roast. Moving for 1.0 to 1.25 so 1.5 and lastly, we see, the percent extraction following the same separation of rows, but just not as clean, not as well defined.

Heather Ward: Scott’s new slide has the same principal component analysis graph from earlier, but this time there are four circles within it. The top left circle captures data points with flavor descriptors of ‘sourness’, citrus’, ‘dried fruit’. The top right circle contains flavor descriptors of ‘astringency’ and ‘bitterness’ while the lower right circle contains the words ‘woody’, ‘earthy’, ‘rubber’. Finally, the lower left circle contains ‘blueberry’ and ‘sweetness.’

Scott Frost: This is the key part for your Principle Component Analysis. We can then take these loading attributes. These are the descriptors. We can make assumptions, we can make comparisons between the position of the sensory attributes with the positions of the coffees.

So generally what we can do is we can overlay these on top of each other, but it’s very difficult to see for a presentation. So I’ve slipped it up. I’ll show you what we got. So this first one here, we see that that the sourness, the citrus, the dried fruit, and the fermented characters are highly associated with these light roast coffees.

Heather Ward: Scott is referring to the top left circle which contains flavor descriptors of ‘sourness’, ‘citrus,’ and ‘dried fruit’.

Scott Frost: We can see roast coffees are positioned up here quadrant of the PCA, and these vectors are pointing up into that quadrant.  We can make observations between where these sensory attributes are located in relationship to the location of the coffees.

Down here we have these low TDS brews being associated with sweet on roast with blueberry and sweetness. These burnt wood, ash roasted thickness attributes were associated with dark roast coffees. and the flavor, persistence, bitterness, astringency related to higher TDS.

That’s great, the PCA is super cool,  geek out on sensory and whatnot. What we really want to talk about, what we really want to know is how, what we did relates back to the Brewing Control Chart.

If we imagine the Brewing Control Chart as a three-dimensional cube right. So we can look at percent extraction along the X axis. Total is all solids along the Y. and if you think about a Z component being attribute intensity,  imagine like a cube.

If you’re looking at it and you can see these points within the cube. What we do is we fit a curve into that points within that 3D space as shown here. So these points here are clearly moving up and out towards you and we fit a curve to those points. And if you take that curve, you take this 3D box and you’re looking at it and you look down at the top of it down as the axis. It looks like a contour map like a Topo map and we get something like this.

Heather Ward: Scott’s slide is titled “Response Surface Methodology.” He is presenting 3D graphs showing the prevalence of certain flavor attributes, such as ‘sourness’ and ‘sweetness’ and how intensely these flavors are perceived relative to different TDS and Percent Extraction combinations and roast levels. When these 3D graphs are turned to 2D, they look like hiking maps with contour lines.

Scott Frost: So this is looking straight down the Z axis, the attribute intensity. And so we have plotted here, extraction percententages along the X axis, strength along the Y for each of the three coffees, light, medium, and dark roast.

So we can look at this the same way. You look at a topographical map, moving from this bottom right corner. We can see increasing sourness as they move across and these things are actually color coordinated or color coded. So this dark or the reddish brownish, whitish is a higher intensity in sourness than the green

That’s what the lines are indicating. So medium roast has a similar relationship, but less important for the TDS and then for the dark roast coffee, we saw this, this local maxima, and I plotted down below for this the three dimensional cubes to really help drive it home, to really help see how these things are.

We can see as we move across the cubes from light roast, medium roast to dark roast, we can see a decrease in sourness overall decrease in sourness. So I picked out six different attributes to show you guys today, a sweetness being next. So same thing, we can see decreasing sweetness with decreasing TDS was not much dependent upon extraction for the light roast.

As we move from the medium roast, we can see that extraction percentage becomes an important factor. We can see this roast effect for sweetness. So linear relationship, the highest intensity at the lower percent extraction TDS pair. Down here at the bottom and percentage traction becomes more important with the darker roast coffees.

So bitterness, exactly what we would expect, increasing bitterness with the increasing roast. We also see with the light roast coffee, higher bitterness up here at the TDS percent extraction. Same thing with the dark roast, but the medium roast gave us this little swirl, right there in the middle of this local minima.

From there the intensity within the medium roast coffee of bitterness increased pretty much straight up with increasing TDS. Burnt Wood Ash so this was the perceived flavor of campfire, effectively within the coffees. We see for the light roast coffee this increase of this burnt roast, this Burnt Wood Ash character with the increasing roast, we see this local minima here in the light roast coffee.

Then we see it moving up into the upper right-hand corner of the light roast coffee and moving into the medium roast and the dark roast doing the same thing. Overall, the darkness was far more… and as we look at this, we can see that the arrow, this direction of ascent. It’s becoming more and more dependent upon TDS for this particular attribute.

So I would assume that if you roast it even further out, you would get very little dependence on percent extraction for this particular attribute.  So local light roast minima increase with TDS and percent extraction and less related to 2% extraction with roast. So flavor persistence.

For me, my interest in coffee, as a personal interest comes from these texture over coffee. So things like body, viscosity, stringency the way it feels in your mouth and tasting aromas are awesome. Don’t get me wrong, but a lot of it comes from me, from my personal preference is the texture terms.

So these next three we’ll read some of the texture terms that we came across. So this first one here is flavor persistence and we defined flavor persistence within the panel as the perception of the coffee flavor after you expectorated or swallow it.  So what we found was with the light roast, there was this maxima. It reaches this point which you get up into the higher index is higher percent extraction, TDS pair, the persistence of flavor reached the maximum point and it does this weird swale as we move to medium and the dark roast becomes a linear relationship with percentage fraction and TDS. Overall these are pretty high intensities within the overall experiment. As noted by them being brownish. So thickness there’s similar story.

Moving, increasing thickness of the coffee with roast. As we move from light roast, medium roast to dark roast, it becomes even more and more dependent upon TDS. So increase with roast in the linear relationship with TDS percent extraction.

I just showed you a small subset of what we came across and for each of these coffees, we had six to 10 or 12 different attributes that came significant. For example, some of them, like black pepper were only significant for one of the roasts. And so we’ve, I’ve included it here, but now, okay, I have shown you guys some fancy boxes and green lines and stuff like this but how can you take some of this stuff home and use it at home? How can you implement this like tonight when you go home and make yourself your coffee tomorrow morning. So the first thing we need to get rid of these little silly lines in this ideal box, and if we think about the Brewing Control Chart, we can think about it and kind of like four different zones.

We can think about it as Zone A, as being this low TDS, low percent extraction. We could think about a high TDS, low percent extraction zone, high TDS, high percent extraction zone, and a low TDS high percent extraction zone. These four zones with which we can, we can use this idea to evaluate a single coffee.

If we started our coffee evaluation, you’ll need some things when you do this at home, you’ll need coffee to start with and a brewing vessel. You can use your Chemex or V60, however you brew your coffee in the morning. A balance would be very helpful.

It would be helpful to calculate the precincts fraction in the TDS. If you don’t have a coffee balance I don’t know what to tell you. These four zones. So if we asked ourselves to brew one coffee within each of these zones, we had all four of those coffees in front of us.

We could make an evaluation about giving coffee about how this coffee changes with index. So if we started down here at this low TDS, low percentage extraction at a brew ratio of 18 to 1 to one brewed that coffee there, and the second coffee would be brewed at 12 to 1 in the high TDS, low percent extraction, and these two coffees are tied together by what we could call a fast port.

I say this because in our experiment, we the almost 100% duty cycle to brew coffees on that side of the chart. So when I say fast forward, the idea being you want to get the water through the coffee grounds as fast as possible without clogging the filter. So then to move to the other side of the chart, coffee, A and C would have the same brew ratio, about 18 to 1 and this would be the slow pour and the sense of add the water.

Stop, hang on for a minute, add the water stop, hang on for a minute. The idea being that you would brew C and A, or I’m sorry, C and D with the same pour, the same slow, methodical pour, and you would brew A and B with this fast pour, and what it would do is give you these coffees across the chart and then you could set them on your table pour them in your cup and ask yourself these questions,  How does the bitterness change? How does the food present itself among these four coffees? How does the aroma of blueberry change? How does the sourness change, the sweetness change? And then maybe you could even say, I want to brew my coffee.

I want to brew coffee A or my favorite coffee up here and I’m going to brew my other coffee down here for differences in my shop or my home, whatever.

The one thing that you need to also consider too is don’t change the water mass with the temperature. So when you make the adjustments on the brew ratio, you got to change the mass of the coffee added.

So, Thank You slide. These are the lab members of the UC Davis Coffee Center. Xian, down over here somewhere. He was the one who did a whole method of work programming the brewers, learning how to run those Curtis brewers. He knows probably just as much as the [technicians behind] those brewers.

Mckenzie Batali doing some excellent work on freshness in your coffee and your taste attributes that change with time. Ziru Mo who has a poster outside looking at the price index of cones and baskets within the market.

Andrea Cotter who’s a new student, who’s going to be doing some consumer work. Jean-Xavier and William Ristenpart who are the people in charge of all of us. We also need to thank Breville and the SCA for the funding, Blue Bottle and Royal for donation of coffee, and Java City also donated coffee for us.

So thank you.

36:15 Audience questions 

Scott Frost: So we have time for questions.

Heather Ward: An audience member is asking why the brew time for some of the brews in the experiment went over 15 minutes.

Scott Frost: So in order to get the pulsing sequence to run like that, so if you imagine if you had a sequence where it pulse for 20 seconds and you stop for 20 seconds and the pulse for 20 seconds. In order to get all 300 milliliters of water out, it takes a long time. So 20 seconds on, 20 seconds off.

So when we did the experiment, it’s only on for the same amount of time, but if you imagine it’s on for a little bit and then we wait, it’s on for a little bit, and then we wait. It spaces it out across time.

Heather Ward: The same audience member is saying that the coffee will be in contact with the hot water for a long time.

Scott Frost: Yeah.

Heather Ward This audience member then points out there’s a goal cup standard and he asks why Scott didn’t use it throughout the experiments.

Scott Frost: So the gold cup standard is meant to hit you right in the middle of the chart right there. So we wanted to be able to brew all the way around the chart.

Scott Frost: Pull up that other slide here.

Okay. What we, what we did with this, with this preliminary experiment was we were looking at using this pulsing sequence and what you’re asking about, so this one here is 20% duty cycle. It’s this orange color and it plots right here at the top end of the chart. So 20% duty cycle would be on for 20 seconds off for 80 seconds on, for 20 seconds off for 80 seconds, and in order to get all the water added to the coffee, it took 15 minutes to get out there, cause it off for so long. So, the longer the brew is, the longer the pauses between, the easier, it just slid right up the brew lines, up the dose lines, and so we could then take and use a little bit of mathematics to decide, “yeah, so we need to adjust it little bit to get it to come up and fit into that position by adjusting the grind or adjusting the dose to fit that spot”. So the brewers were all programmed to dose the same quantity of water just at different seconds. Yes,

Heather Ward: An audience member is asking why the experiment adjusted grind size.

Scott Frost: So that’s a good question. So with the darkness, we didn’t need to adjust the grind size, but the other two, you needed an adjustment in grind size. So when you adjust the grind size, when you grind finer, you get a stronger coat. So the grind allowed it to, spread it out further along the dose lines, cause we really wanted to be able to brew a coffee at 16 and 1. So we needed to grind it properly to really spread it out across. The intent was to have a cup of coffee with a particular TDS for some extraction.

Across the three roasts, the grind, or I’m sorry, little dose and the percentage track or the dose and the duty cycle or the same, we needed to adjust the brine for the different coffees.  That was the major thing that we changed.

Heather Ward: An audience member is asking what the average weight of the coffee used for brewing?

Scott Frost: The mass in the brewer range from 121 grounds all the way up to 252 grams.

33:30 Heather Ward: The same audience member is asking how many cups they brewed.

Scott Frost: The volumes that came on, I can’t remember off hand.  It was attempting to brew almost a liter of coffee, or I’m sorry, I’m just a gallon of coffee. Yes, it was 3000. Yes, we were approaching a gallon yes. No, but we didn’t get a yield of a gallon with these higher doses because more than the water is retained within the dried, within the brew bed but we kept the water, the constant across the brews.

Yes, sir.

Heather Ward: An audience member is asking Scott to explain what percentage extraction is.

Scott Frost: So if you conceptualize putting coffee into a brew basket, right, and pour water over the top of it. See now have coffee removed from the dry coffee. It’s the mass amount of coffee removed from the dry coffee. It’s yielded exactly the yield. Yes

Heather Ward: An audience member is asking Scott to explain how they controlled water temperature in the coffee slurry. They point out that using different pulsing cycles would affect the slurry temperature in-between experiments.

Scott Frost: Yes. So I think we see, we see that phenomenon out here with these particular brews. So for example, this one here, this red one, you can see that it’s, if you imagine a dose line running up like this in a out like that, it kind of. Yes. I think what we saw is that when you go sit for a second and wait, you know, if you dose for 20 seconds and then wait for 80 seconds, you get temperature fluctuations within the coffee.

And I think that’s why we’re seeing this variability. It’s a hypothesis, it’s a guess. But if we, overall, the distribution and TDS within that treatment is pretty small. It’s about 0.1. These brewers were pretty cool, so we were happy with their ability to be reproducible. If for some reason we were brewing at this 20% duty cycle and,  we got this crazy, spread, we would’ve tried to do something different, but yes but no, you’re absolutely right. I think we do see temperature fluctuations within the higher, within the lower duty cycle coffees.

Yes sir.

41:15 Outro

Heather Ward: That was Dr. Scott Frost at the Specialty Coffee Expo in April 2019. Remember to check our show notes for a full episode transcript of this lecture and a link to coffeeexpo.org for more information about this year’s event.

This has been an episode of the SCA Podcast’s Expo Lecture Series, brought to you by the members of the Specialty Coffee Association, and supported by SAP’s Softengine Coffee One. Thanks for listening!

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