The need to calibrate

On bars these days you find more and more usage of scales and thermometers but less and less interest in calibration. Like most things, there is a balance between dependence on something and willingness to check that what we depend on is accurate.

Here are a few things to calibrate and a few easy ways to calibrate them.

Scales: Some scales come with a gram weight which can be used for calibration. Alternatively, you can purchase a set of weights for calibration purposes. For your small scale that would be measuring amounts such as gram doses, a nickel is a good calibration tool. A nickel weighs 5g and once you have zeroed and tared your scale, you can simply place a nickel on it to see if it is accurate. A better way of calibrating a scale though is to measure the maximum capacity of the scale. If the scale maxes out at 5lb, finding something like a 5lb bag of sugar to measure the maximum of the scale. RTFM applies in all situations as many models of scales have calibration modes outlined in the manual.

It is also a good idea to make sure the scale you use for measuring small gram dose weights has a small enough resolution to be practical. Some scales have resolutions that vary as much as 5g as they are designed for weighing larger amounts, some are used for precision measurements of small amounts but need to be tared often or reset and tared between measurements.

Thermometers: Thermometers are easy to calibrate and hopefully everyone manual brewing coffee is measuring temperature. To calibrate a thermometer, simply fill a cup with mostly ice and a little bit of water allowing more than 80% of the probe to be submerged. Let the thermometer sit submerged for one minute and then observe the temperature. It should measure at 32f/0C. In conjunction, a measure of water at a rolling boil can give another data point. Placing the same probe into water at a rolling boil should give you a measuring point of 212f/100C unless you are at high elevation to which your boiling point may differ. (To verify espresso temperatures, we recommend getting a Scace and calibrating it the same way in both ice water and boiling to establish group head temperatures.)

Note: The usefulness of calibrating thermometers was most apparent for us. With our installation of two roasters (identical), we found the temperature probes (and spares) had a range of variance within 2 degrees. After identifying the offsets, we then programmed this into the displayed temperatures. When changing the temp probes, we would have to repeat the process of calibration.

Flow Meters: The traditional flow meter in an espresso machine is one of the most difficult items a professional barista can use. In many cases, we tend to abandon this because constant recalibration is needed. The reason being that in the dual boiler machines we use, the volumetric component isn't designed for precision and is placed in a position where hot water sits and scale buildup occurs. This creates many problems that makes it less than useful and often a hinderance. Recalibrating involves either a scale weight of the resulting shot (remember mL and grams are exchangeable) or a volumetric estimate with a 'shot glass.'

In the next year, a new type of flow meter will be introduced in coffee brewing that should not be confused with the volumetric controls on an espresso machine. The LuminaireCoffee volumetric controls are a generation ahead in that they function with more accuracy and are more useful in what they display. As opposed to the volumetric controls on an espresso machine, the LuminaireCoffee flow meter is in the cold water section and has less issues with buildup or hard water. It also is precision and digital which is best exemplified when using it in manual mode as it functions similar to a chronos display of time on a La Marzocco espresso machine. It simply displays total cumulative volume and time counts (and a dynamic flow in either ml/s or oz/min) as you are brewing. (In preset mode, it has cutoffs that can be set to stop the flow at either time or volume points.) Calibration of this is done at production but can also be done by measuring a specific volume of water in a specific time count with a calibrated scale. It makes brewing onto a scale to measure volume a bit superfluous (once calibration is verified). See Flow and Profiling posts for more relevant discussion.

It's all about the flow (or it should be)

When talking about v60's and most hand pour methods, the discussion always breaks down quickly with vague terminology. The chatter comes back to a simple and sometimes meaningless statement of total water volume (usually in gram weight), total brew time, and relating extraction %. That's the hot thing right now in espresso as well in drip, to look at the yield, not how you got there.

The truth is that how you got there matters a lot more. In fact, it's everything.

Looking at the end result is myopic but it's easy and makes sense because it doesn't require much investment. Developing the whole picture takes more than just looking at a few parts and will continue to escape us until we become more scientific in our methods and less what if in our blog posts. It is however what's trending so we deal with tons of discussions bogged down by vague statements.

Here is a simple premise. What if we threw out the scale and stopped measuring the results and moved to a discussion focused on flow rate, intervals, and then talk about the yields?

I know, crazy stuff.

Instead of talking about 12oz, 3-4min, and yield... we just say 4oz/min to 12oz at x dose = yield. It makes a lot more sense to really talk about flow, but only if the flow is fixed and measurable. A steady flow rate is easier to make this functional than a stop start method because the real problem with stop n start methods is the inability to accurately repeat what was done. The yields vary greatly and lack consistency. It takes an awful lot of artistic skill to eyeball measure a volume of water and pour small amounts of water at intervals with any kind of repeatability.

This is the entire case for putting a flow restrictor to a kettle to get a fixed and steady stream. It is also the same premise behind the LuminaireCoffee Lb-1. Instead of incorporating a clunky scale (which you can happily buy for around 20 bucks and add on your own) that would cost another thousand to integrate effectively, they put a precision flow meter inline. That means there is a functional and precise measurement on their display of flow (volume over time). This is incredibly useful and rather intuitive once you get used to seeing it. Having that display also makes for less guess work when trying to dial in a brew.

Take the assumption in the next three cases of a 2 cup paper v60 (more elegant in metric but be patient with the oz/min instead of ml/sec):

Case A: You could conceivably brew your preinfusion at 5oz/min over 15sec with a pause of 25 seconds, then brew for 2 minutes at 6oz/min. Total volume of about 12oz if you assume the preinfusion stayed in the brew cake. Total time would be 2:40 plus the 30 seconds (3:10) it took to drain unless the grind was coarser or finer.

Case B: Alternatively, we could conceive a brew with 5oz per minute over 15sec with a pause of 75 seconds. Then follow with one pour at a flow rate of 12oz/min over 1 min sec. With a draw down assumption of 40 seconds (drawdowns are often longer with more aggressive pouring), we'd have a total volume of 12oz in (3:10).

Case C: Finally, we take a 5oz per minute preinfusion over 15sec with a pause of 30 seconds. Then an off on pour of 12oz/min 4 times for 15 seconds with 3 intervals of 20 seconds. (Doing the math to add that up is as confusing as trying to brew it consistently.) The draw down would be roughly 40 seconds making an overall time of 3:10.

With Case C: Making sure you were precise about the intervals/timing/volumes would take an Lb-1 or ninja kettle skills to be repeatable. Case B is the easiest if you don't have a good kettle, and case A is the one if you have a controlled pour or want the most repeatable (less agitation dependent/easier to get repeatable yields from our experiments). These are just examples and a tweak to grind on each could get the same yield throughout at the sacrifice of some time consistency.

In having a discussion, you see people talking about the starting weights, and the ending times/intervals, but there is no discussion about flow. Why? Because it's hard to measure and hard to control. If you had this in your equation and it was easily measurable, you have a real serious (but complex) discussion. Instead of listening to person in case C talk about a pre-wet and then 12oz pour with 'intervals', you could have a repeatable brew equation that can be tested by others with the same coffee. We can record the resistance of a filter then develop a metric for resistance in the grind and how that is changed by the different flow rates (and resulting agitation). Segmenting each interval and testing it would take time but you could actually have a real discussion about what is going on.

Do it in mL per second and the whole thing becomes quite elegant.

Sadly, espresso machines need this most but current designs have no ability to integrate this. A precision display giving an accurate volume over time which would then make measuring yield very useful. Right now, measuring the gram weight then deriving tds and extraction % of a resulting shot (without a specific incorporation of time and flow) is actually a graph of one variable against a derivative of itself. That is not as useful as it seems more than to calibrate yourself with the same coffee on the same machine with the same water at the same temp with the same grinder to repeat a previous good shot of espresso. That is not how it is being used but much like most things in coffee, we talk a lot about things we aren't always doing ourselves.

Having access to these controls has really hardened my belief that there is so much more exploration to be done and we need to be unbound by things like the gold standard. Sure it is great for a bulk brewing traditional cafe but in our segment, what if there is an amazing cup slightly out of that range? Having a precision range of temperatures and being able to switch temperature mid brew has been devilishly fun to work with but also present a contrast to how most people are still stuck at one temp and a declining or a 'sloped' brew temperature. Having precision and easily adjustable flow rates will be the next thing to really play with on the newest version of the Lb-1 (that will be in production in the spring). When other people get them, we'll compare notes and see how the conversation changes.