Verification of Development Using a Refractometer
A coffee’s extraction potential depends on roast development. Inadequate development will limit a bean’s solubility, and hence its extraction. For example, let’s say you roast two batches of a coffee to the same color and pull several espresso shots from each batch using identical inputs (temperature, time, ground weight, shot weight, and so on). If batch A consistently yields extractions near 19.0% and batch B averages 16.5%, batch A is almost certainly more developed than batch B. In such a case a refractometer offers objective verification of roast development.
The coffee refractometer has had more impact on coffee quality than any other invention in decades.
13: Sample Roasting
All the principles of roasting on a large machine apply to sample roasting. Many owners of small roasting businesses have commented to me that they usually prefer the coffee made from their sample roasters to that made from their production roasts. That’s not surprising, because sample roasters often have more power than small shop roasters, relative to the small batches they roast. A high ratio of gas power to batch size facilitates good development. However, most sample roasters have rudimentary controls, making consistency challenging.
Sample Roasting
Most older sample roasters offer the user only two controls: a manual knob to control the gas setting and an environmental probe. To make the most of such a machine, I recommend using the following procedure:
Stabilize the roasting environment at one particular temperature between 410°F-420°F (210°C-216°C), with the drum empty before charging.
Charge the coffee and do not change the gas setting.
About 30 seconds before first crack, decrease the gas by approximately 40%. If this produces a very fast roast (less than 8 minutes) or a very slow one (more than 13 minutes, which is slow for a sample roaster), try changing the pre-roast stabilization temperature.
Aim for a 9-11 minute roast.
This strategy is simplistic but often yields surprisingly good results and consistency, given that the operator doesn’t have much feedback or control while roasting.
Six-barrel sample roaster
Ideally, one should use a bean probe when sample roasting. Beware, though, that in many sample roasters it may be difficult or impossible to immerse the probe in the bean pile sufficiently to produce reliable temperature readings. If your sample roaster doesn’t already have a manometer or other precise indicator of gas setting, I recommend investing in one. When using a sample roaster with adequate controls (bean probe, air probe, manometer, and so on), one can roast exactly as one would in a production machine, though one might consider using faster profiles with a sample roaster.