confounding variables

Observation 1. Batch brewing is often associated with bad tasting coffee.

Observation 2. Manual brewing is often associated with good tasting coffee.

In other words batch brewing correlates with bad tasting coffee, manual brewing correlates with good tasting coffee.

What is the conclusion?

Is it that batch brewing is the cause of bad tasting coffee, or that manual brewing is the cause of good tasting coffee? Both?
If batch brewing is the cause of bad tasting coffee, then all batch brewed coffee should taste bad. If there is even one exception, that suggests the hypothesis is false.
There are of course confounding variables (such as):

People who manually brew are more likely to care about the taste of the end product. [that isn’t to say that everyone who manually brews cares about the taste, or that everyone who batch brews doesn’t,  just that on average one group is more likely to care than the other]

They are more likely to (among other things):

  • use nicer coffee
  • use appropriate brew ratios
  • use appropriate grind settings
  • grind fresh
  • clean their equipment

It is these considerations, not the choice of manual brewing, that results in the odds of me getting a tasty cup of coffee from a manual brew being higher than from batch.

In a similar way to my initial mistaken conclusion above, I could correlate skinny jeans to good tasting coffee. I might observe that if a barista or team of baristas seem to have a preference for skinny jeans I have a higher chance of getting better tasting coffee. This might correlate quite well, but should we conclude that this clothing has an effect on the taste of the beverage?

Less absurd perhaps is the presence of latte art on a cappuccino. I might observe that cappuccinos that I have received that have latte art on them tend to taste better on average than those that do not. Does latte art cause the cappuccinos to taste better? Or is it more likely that there is a confounding variable?


20 thoughts on “confounding variables

  1. J says:

    I may sound like I promote Bunn, but I have noticed that when used correctly, they match most single brews at any given time. This is because what most customers look for, is consistency in their cup. I’m going to stick my neck out there, but in Stockholm where I live, not enough people use the proper techniques nor tools to consistently brew single brewed coffees, to match the batch brewers. Yet.

  2. The key variable isn’t batch vs. manual. It’s automated vs. manual. That, and the fact that when your brew yield (batch size) goes up, certain variables change that makes certain flaws in the brew less of an overall issue.

  3. Mike Haggerton says:

    Whilst I do believe that manual brewing has the [i]potential[/i] to produce a greater cup on a more consistent basis, that only works if the barista is knowledgeable, skilled or passionate enough to make the necessary adjustments throughout the day, week and lifecycle of that particular roast, to hit the target strength/extraction range. But my suspicion is that the knowledgeable, skilled barista soon becomes a trainer of staff who don’t have the same passion to learn and effectively become coffee-pouring automatons, never correctly making the essential tweaks in technique (e.g. your confounding variables). Quality becomes variable – if you took a periodic average of taste quality it would be a declining chart. In that scenario there’s a very good chance that a batch/automated brewer produces a larger number of good tasting coffees (provided basic rules are followed).
    That said, it’s manual brewing for me all the way, and the issue is one of staffing rather than brewing equipment.

      • Mike says:

        Yeah, that’s what I was saying Colin. To me it seems that there is a choice… either:
        (a) accept that it is too difficult to train and retain good enough staff to consistently perform manual brewing properly, and therefore switch over to automated batch brewing, which will do a better job than bad staff, or alternatively;
        (b) push the boat out on staff recruitment, training and development so that you build a team who can successfully perform manual brewing to a high standard on a consistent basis.

        I don’t think there’s a right or a wrong choice… it’s horses for courses… but if the end goal is the best quality coffee on the most frequent basis then IMHO it’s (b). It is more difficult and more costly, I think, but has a better chance of consistently delivering the best tasting coffee (along with the other benefits of investing on staff).

  4. Stijn Braas says:

    I’m really not getting what you are saying, or you are wrong. I sincerely hope the first. You compare ‘batch’ and ‘manual’ brewing. Are those polar opposites? On the short discussion we had on Twitter, I misread your article in which you never mention quality, just bad or good tasting coffee. On Twitter you say two methods, all other things being equal, should taste the same (have the same quality). This is going quiet a bit further. Are you saying it won’t matter which method you choose (bunn, v60, press pot, espresso), the result should taste the same? Why are we bothering with all these methods then? Why is there such a thing as manual brewing?

    You are right about statistical significance and statistical meaningfull correlations being two different concepts. But to compare those to skinny jeans or latte art is just not right.

    • No, they are not polar opposites, they are two methods of brewing a cup of coffee. One has negative associations among the high end coffee community, one has positive associations.
      Why is there such thing as manual brewing? Originally it would have been intended for domestic use I imagine. However, there is a desire to make the coffee to order, which may have its merits. Manual brewing also comes with none of the negative connotations associated with batch brewing which have been ingrained over decades.
      Ultimately I think you are asking me, do I think I can get as good a cup from a batch brewer as I can from a manual brew? I would suggest I can, and that it is far easier to achieve, and to achieve consistently on a batch brewer.
      Whether batch brewing will or should come back is another question. I do see merit in to-order brewing, however, it is difficult to advocate per cup brewing when so often it is done so badly… by supposedly expert baristas.

      • Stijn Braas says:

        I agree batch brewing has some negative connotations it doesn’t deserve. Then again, other methods apart from espresso all have some of those. When we talk about batch brewing we typically talk about it in a commercial sense – what do consumers want? The negative experience of quality it has is difficult to ignore for coffeeshop owners. Could it be as good as manual brewing? May be, for sure. Does it create a similar experience of quality? Not at all.
        I think what you are saying is that the qualities of the barista is one important factor in getting a good tasting cup of coffee. I agree. Should we then opt for a method to make things easier for baristas but create a worse experience for the costumer? I think we should work on the expertise of the barista.

  5. As a consumer, when I see a batch brewer at a shop, I am always afraid that brewed coffee, to that shop, is of secondary importance next to espresso. It can imply a “set-and-forget” mentality toward brewed coffee. I fear, since everything is assumed “dialed-in”, that nobody will be paying any attention to the beverage that is coming out of it. It implies a focus more on speed of service than of quality of cup.

    What’s more, if, after setting a batch up and brewing it, it is discovered that the resulting beverage is not up to standard, an entire batch of coffee has been wasted. My fear is that since each batch is such an “investment”, that there will be a reluctance to throw out a batch of coffee, even if it is deemed sub-par and that, since a batch brewer is normally inserted into the workflow in order to save time and people-hours so that more worthy things can be attended to, that my calling attention to a bad batch will neither be appreciated nor attended to.

    Manual brewing, while certainly no guarantee of a superior cup, infers that *each cup* matters and is worthy of as much attention to detail and use of craft and skill as each shot of espresso.

    In addition, as had been highlighted by many a shop, sometimes a coffee can benefit from a particular brew method. If every coffee is tied to a single (in this case, batch) brew method then, again, it leads to a conclusion that brewed coffee is not worthy of the same amount of attention to detail and quality that espresso is, with its focus on different grinds, temperatures and pour volumes not just from coffee to coffee but from shot to shot throughout the day.

    So, yes, correlations and not causations but, skinny jeans notwithstanding, there’s nothing wrong with pulling meaningful data from correlations, especially if those correlations are repeatable.

  6. I believe that whether it is batch or brew, skinny or baggy jeans, bow tie or tuxedo printed shirt, it comes down to a psychological issue.

    Speaking about manual brew, by the cup, it does have an appealing aesthetic look to it. Someone serving me a cappuccino wearing baggy jeans, chains and a sweater two sizes too big, well I’d say I would be a little reluctant to ask that person to serve me. Let’s take that same person and suit them up in those skinny jeans and stereotypical hipster clothing and personally I would be ordering coffee from that person more than once.

    A cappuccino with latte art will unfortunately always be, in my mind, better than one without, even though it was made the same.

    In regards to batch brewing, I fear the likes of Starbucks and Tim hortons has painted an ugly picture for those entering, or already in, the specialty coffee industry. A picture that says large batches of brewed coffee are shit compared to a single cup brew from an aero press. Maybe it is. Maybe batch brewing has not been brought to almost perfection like manual brewing has been. Maybe it can be better than we think. Maybe batch brewing needs a new invention to bring it to the high standard that conniseurs are used to.

    Maybe a 6L Chemex needs to be built. =P

    I could be completely wrong.

    • “Manual brewing, while certainly no guarantee of a superior cup, infers that *each cup* matters and is worthy of as much attention to detail and use of craft and skill as each shot of espresso.”

      You can infer that but it never proves true. Baristas freak out if an espresso machine isn’t temp stable to less than a degree F, but will serve a manual brew that extracted 25 degrees F less than ideal.

  7. If a barista doesn’t look at a batch brewer as a button to push, it can taste just as good (while maybe different) as manual brewed coffee. Ive tasted great batch brews. The variables (not brew ratios) should be changed with the coffee just as one would with manual brewing. Really all we are doing are putting coffee and water in contact with one another then separating them at the opportune time. If that is done properly it shouldn’t matter what the quantity being made is.

    Was it Scott Rao that talked about “concentration area”? That could be the only variable I see manual brewing being better at keeping consistent than batch brewing.


  8. Rob Smyth says:

    I think there’s really two interelated questions being asked here.

    Is manually brewed coffee better than batch?
    In short no. Batch brewers can create just as good a quality cup of coffee, arguably more consistently, as manual brewing, all other variables being consistent.

    Realistically, is a manually brewed cup of coffee, prepared by your stereotypical hipster barista, likely to be better quality than than most batch brewed coffee available?
    In short again, yes. Proportionally batch brewed coffee offerings dwarf manually brewed coffee. But even the worst manual brewed coffee is still likely to better the average batch brewed coffee. Even if the skills & consistency of the barista are likely to affect the quality of the cup, it’s also likely if a cafe has gone to the effort of serving manually brewed coffee, some consideration has gone into coffee selection, brew ratios, water quality, etc. The same is certainly not the case for the vast majority of cafes offering batch brewed coffee.

  9. I know you know this already and think you’re writing solely from personal experience, but batch brewing doesn’t correlate with bad tasting coffee, poor extraction parameters correlate with bad tasting coffee and that can apply to both manual and batch brewing. It’s a tough argument to moderate until average slurry temps of manual brews rise out of the 170F range and baristas start calibrating batch brewers the way they calibrate espresso machines. A good batch brewer when calibrated for temperature, water mass dispensed, even distribution of water over the grounds, and total contact time will, in the right hands, give you a more consistent extraction over the course of a service than one or many baristas trying to serve via single-cup brewing methods.

    Yeah you lose the theatre, but baristas overestimate how much the average customer wants to watch them pour water over coffee grounds.

    • “but batch brewing doesn’t correlate with bad tasting coffee”

      I think in many people’s experience it does. The underlying cause is moot, because people aren’t aware / don’t care.

      Other than that I think we are in agreement…?

  10. Brandon Paul Weaver says:

    My inclination is that those shops using batch brewers (often *solely* using batch brewers) are more concerned with efficiency (and thereby labor/cost effectiveness) than quality. The automation of a batch brewer allows this shop to spend less time on training and less time per cup and therefore, in many ways, save time (i.e. money).

    All this means is that this shop associates *value* with a lack of investment in training. This lack of training translates into the baristas not being able to understand what they are tasting, (e.g. what an overwhelming bitterness might mean about their brew ratios etc.). This results in terrible batch brews.

    With adequate training, I see very little reason why a batch brew would be dramatically poorer than a single cup.

    Of course there is distinct *value* in the customer experience of a single cup brewed to order. This often leads to enthralled customers who return and engage in a new way.

  11. Sort of missed the boat on this one but a good discussion, heres what I think.

    One large reason batch brewing tastes inferior is because lots of coffee shops want to offer it as a cheaper alternative to an espresso derived brew, once they discover that serving good quality filter coffee actually costs more than its distant cousin, an americano, something has to give. Rules get broken from brewing ratios to the quality of the coffee and all of a sudden batch brewed coffee tastes bad. All our fault and now batch brewed coffee has such a bad name that a blog is written about it.

    What can we do about it? because I love filter coffee, I love automated filter coffee. I also recon that automated equipment will give a more consistent and higher quality result most of the time over manual brewing.

    What makes an an espresso brew have a perceived higher value? One very strong reason could be that it is an individually brewed coffee, whereas a batch brew is not, solution… Come to my place and I’ll individually and automated brew you a small (500ml) jug of filter coffee for you to sit down and enjoy by yourself or to share. Perfect. Easy to do easy to repeat. Problems of manual brewing solved and no more batches. Sorted…almost.

  12. Pingback: Latte Art 101 | New England Brewing

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