Coffee Roasting Series #3 - Charging and Soaking

1. Charging and Soaking  

Setting your charge temperature is first step to set momentum. A good starting place is around 400F. Denser, larger, or washed coffees can take slightly higher charges. Decaf, natural, and smaller varieties absorb heat easier and need slightly lower charges. Charge temps can be machine specific, so I would look and see, generally, what other people with your machine charge at.


When turning on your machine, you want to preheat your roaster for at least 20 minutes at about 40 degrees higher heat setting than your actual charge temperature. Then reduce temperature to your charge temperature for another 20 minutes. This thoroughly heats the roaster in areas that your probes are not located, so you are not also heating the roaster while trying to roast your beans. If using some kinds of small home-roasters, your preheating can go much faster.


Your charge temp will also vary based on what percentage of your roasting capacity you are using. Generally, it is recommended to stay around 60-70% of roasting capacity, and there applies the 400-degree recommendation. Many roasters are roasting at 90-100% capacity, so the charge temperature will necessarily be much higher. The cool beans absorb all the heat, and the more beans you have in one batch, the more heat will be absorbed upfront.


To Soak, or Not to Soak? Soaking allows beans to absorb the charging heat gently, without a lot of extra heat being added. This means the inner bean temp is catching up to outer bean temp more easily. You can imagine that heat is slowly passing thru into the inner bean at charge. If you push a lot of heat onto the outer bean, that outer bean will heat faster than the inner bean. This problem is especially true during the drying phase, as the bean is at its densest, and heat moves into the bean the most slowly.


You can soak with no heat, or soak with a reduced heat. Many excellent roasters do not soak at all. High density beans benefit from applying a good amount of heat during soak, before ramping up to your highest heat (highest for this roast, that is). Whether you want to soak or not may be machine-dependent. Small home roasters that lose heat easily will not be helped by soaking. The danger with overly aggressive soaking is that you lose all the heat that you built up at charge, and now all your momentum is gone.


Inner bean development during dry phase can be thought of as building the inner bean momentum. Flavor-producing chemical reactions (hereafter, Flavorful Reactions) that occur later in the roast need lots of momentum. If you fail to build that momentum in the drying phase, your coffee will taste flat, cardboard-like, and dull. A good rule of thumb for most roasting machines is that dry end should occur between 5 and 6 minutes, give or take 30 seconds if roasting very fast or slow.


It is possible to achieve this Dry End time without having built the necessary momentum. That is because your probe, or your bean color reading, does not give you a read on the inside of the bean. It is only reading the outside.


If you blast thru Dry End on a very dense high altitude Guatemalan bean, you risk roast defects, and the inside of your beans may still be underdeveloped. If you use lower heat to extend the dry time, trying to correct your mistake, then you easily might not give the inner bean the momentum it needs. A balance is necessary. But you can see how a bean takes heat, by how quickly it responds to heat compared to other beans.


Last thoughts on charging and soaking: a fast dry end time risks building so much pressure in the bean that the moisture steams out of its weakest points: the tips. Tipping is as undesirable as scorching or charring. Proper charge temp and soaking at the right heat settings will give you a relatively fast dry time without tipping effects. If you have tipping effects, you should either: soak with less heat, soak for a longer time, or reduce the after-soak increased heat setting. If none of that works, your charge temp is too high.