Understanding heat, moisture and mass transport during the roasting of a coffee bean is essential to identifying how the colour and flavours are produced. This paper first considers a slightly simplified version of an existing heat and moisture transport model proposed by Fabbri et al. (2011), and we show that this model can be fitted well to data for the moisture content of a coffee bean but has some stability issues and lacks some important physical mechanisms. Building on these ideas, a new model is derived from conservation equations.
This model is then simplified; in particular, issues of CO 2 production are neglected as there is currently insufficient experimental data to fit parameters. This new model is fitted to the same experimental data as presented by Fabbri et al. The new model predicts significantly different internal structure and behaviour of the moisture than the existing model, while both show qualitatively similar average behaviour. This is due to the fact that our model tracks local, rather than bulk, quantities. One benefit to this new model is that it accurately predicts the existence of a sharp drying front, which partitions the bean into an outer dry region and an inner moist region. A detailed comparison of the two models is provided, in order to cast light on the relative importance of various heat and mass transfer mechanisms inherent in coffee bean roasting.
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When I wrote The Coffee Roaster’s Companion, I was on the fence about The Soak. These days, I’m on the side of the soak, most of the time. I’m overdue to write about it. What is the soak?Broadly, from what I’ve seen, the soak is a roasting method in which one charges a batch with low-to-no gas and increases the gas to a high setting sometime in the first two minutes after charging.
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Just to avoid the inevitable question, no, the soak does not involve adding water to coffee beans:).The soak is not necessary to produce stellar coffee. But I have found the soak makes good development and clean flavors easier to produce in most situations, with most machines.Why does the soak work?This is my hypothesis— it’s speculative, and I have no proof that this is the reason the soak works, so please take it in stride:In a typical 10–12 minute roast, coffee does not release moisture for at least the first minute, and probably a little longer. This is because a portion of the coffee beans’ mass has to reach the boiling point before releasing its moisture as steam. Even at the boiling point, it’s likely steam won’t be released immediately upon its formation, as the cellulose bean structure surrounding the steam may be too tough, and not porous enough, to allow the steam to escape. So much for “the drying phase.' Moisture released by beans during roasting forms an “evaporative front” that acts like a force field, slowing the transfer of heat into the beans. That's why beans with higher moisture content require more gas during roasting: the heat has to overcome a greater amount of (cooler) moisture to penetrate the beans.Given that there is no evaporative front for the first, let’s say, 1:30 of a typical roast, one doesn’t need to apply as much gas during that phase to heat the beans at a reasonable rate.
Charging with a lower gas setting also has the (presumably) beneficial side effect of lowering the peak drum-metal temperature in a classic-drum roaster; that should produce softer flavors in the cup. Setting a machine's thermal energy slightly higher before charging a soaked batch facilitates development. Therefore, the soak may help softness and development; that should yield better coffee and provide a greater margin for error.But in CRC you advised charging with sufficient energy, and the soak calls for less gas at charge.Good point. When I wrote CRC, I knew that an inadequately-warmed-up machine was more likely to produce underdeveloped coffee. Therefore, a sufficiently hot charge, and pre-charge actions, were important for good development. What I didn’t know then was how much of the “sufficient energy” should come from the machine’s thermal energy and how much from the gas setting at charge.Soaking has taught me that the initial thermal energy of a roaster is critical for development, but the initial gas setting is not.
Please don’t take this concept too far: I do not recommend charging too hot or soaking with the gas completely off. My apologies for not being wiser and clearer when I wrote the book; I’m always learning and will try to comment publicly when I’ve realized I have made a mistake. Unless it’s a really, really embarrassing mistake.:)Should I always soak?Probably not.
Some machines aren’t as well-suited to soaking as others. As well, some coffees seem better suited to the soak than others. I simply recommend you try the soak, but keep an open mind about its benefits and its limitations.CommentsI’d like to hear about your experiences with the soak. Please don’t ask me how or when to soak— that’s a little deeper than I’d like to delve in this blog, and also, a proper answer may require more information about your particular machine and roasting style than would be reasonable to discuss here. Thanks for reading.
The coffee bean is the seed of a sweet ripe cherry. Much like wine, it contains a wonderful combination of flavors from the variety of the fruit as well as the ground in which it is grown. Climate and altitude obviously play major roles in the complexity of the overall flavors of the fruit.
As such, the seeds of the cherry, your future cup of coffee, also carry these flavors; and the real art to great roasting is preserving this character as much as possible. Over-roasting results in loss of most of these flavors, and so it is imperative to us, that even our Darker roast retains the character of our beans.For David’s Roasting, we chose the fluid bed method for several reasons. Fundamentally, a fluid bed roaster is a lot like a hot-air popcorn popper. The hot air is forced through the chamber where the beans are contained, and allowed to circulate around each bean more consistently. As the beans roast, they become lighter, due to the loss of water and are blown around more and more.
This allows them to circulate more efficiently through the chamber. The hot air moves the beans. The temperature sensor allows for a consistent monitoring of the roasting process and we can control it much more accurately. Additionally, the chaff, or outer skin of the bean, is blown off completely and kept away from the beans during the entire process.By contrast, the drum roasting method, rolls the beans inside a metal drum. Contact with the metal drum often creates an uneven roasting process. Coffee roasted too quickly, or with too much heat may also be unevenly roasted throughout the bean. Likewise, coffee roasted too slowly or with inadequate heat will be completely void of the natural flavor oils and compounds.
Much of the burned chaff stays with the beans until the cooling process, adding unwanted flavor. Additionally, drum roasters tend to need a much higher operating temperature in order to properly roast the beans, making it harder to achieve consistent results in a lighter roast profile.Below are several pictures of the roasting stages using our fluid bed process; from their initial green stage, all the way through to the finished product. This takes approximately 18 minutes start to finish, including cooling, depending on the roast level. Green beans In the first few minutes the coffee actually becomes paler as it loses water and dries.
The beans are starting to assume a browner color, and a marbling appearance is starting to emerge. The first “toasty” smells (like toasted grains) can be detected, and less humid air coming off the coffee.Just before first crack. The coffee has browned considerably, which is partly due to browning reactions from sugars. First crack is done.
This is considered a City Roast. The bean surface is smoother somewhat from expansion but still has darker marks in the coffee. The edges of the seed are still fairly hard. At this point the coffee starts giving off carbon dioxide. Full City +, the coffee has barely entered 2nd crack. As you can see, compared to the green beans, these are much larger due to their expansion.
In fact they will often be double their original size. They also flow freely though the entire chamber because they are much lighter.
The compact solutionThe drum roaster P 60 is particularly designed for gentle long-term roasting of high-quality gourmet coffees and espresso. Its special shovel mechanism inside the non-perforated, double-wall roasting drum homogenously mixes the product during the roasting process.The PROBAT-specific air to bean ratio ensures particularly uniform roasting. With roasting times between 10 and 18 minutes, heat is transferred to the coffee beans over a longer period of time, thus guaranteeing a highly intense flavor development.
Due to top-quality workmanship, the P 60 stands out for its high functionality, process reliability and long operating life. Its maximum batch size of 60kg makes the P 60 the perfect roasting machine for larger shop roasters as well as for small scale industrial roasting facilities. The drum roasting process in detailThe heart of PROBAT’s P 60 drum roaster is a horizontally lying roasting drum which is equipped with a rotary drive. Shovel blades circulate the coffee beans during the roasting process. The flame of a burner generates the energy for the roasting air which is guided both through as well as around the roasting drum by means of flaps. As such, heat is applied through conduction via the bean’s contact with the roasting drum as well as through convection via the hot incoming air. uniform bean appearance and homogeneous roast through the combined application of heat via convection and conduction.
specific design of the roasting drum allows for a gentle mixing of the beans. reliable production from light to extremely dark roast colors. long roasting times with high production outputs.
minimal product loss, minimal weight loss. effective and gentle cooling. reduced cycle times by simultaneous roasting and cooling. effective chaff separation by separate, free-standing roasting cyclone.
The P 60 drum roaster is equipped with the semi-automatic PILOT Roaster Basic control system with touch panel, recipe management for 99 recipes and 8 recipe stages. (P60 SA). optionally available as fully-automatic version with roaster control system PILOT Roaster Excellence and recipe management for 999 user-definable recipes. Settings that have been saved are reproduced safely and automatically.
(P60 PRE). fully automated PC-based control system (P60 PRE). clear visualization and simple operation (P60 PRE). overview of all key roasting parameters and temperature curves (P60 PRE). all data relevant to production is saved, allowing it to be accessed and analyzed at any time (P60 PRE). transparent presentation of the system’s operating status in real time (P60 PRE). can be operated directly at the roaster or centrally from a control room (P60 PRE).
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Coffee Roasting Guide Pdf
The insulation jacket is a cost effective way to minimize heat losses. When used in conjunction with a Base or Side Drum heater it reduces the heat up time and energy costsThe insulation jacket can also be fitted after heating the Drum to reduce the cooling effect. Teflon/Polyester jacket. Glass filament insulation.
Can be used with Silicone side drum heaters, Base drum heater. Flap for Filler Access.
Coffee Roasting Temperature
Standard sizes is 200 Litres. Water resistant. Easy installation. Non-standard sizes to order with own logotype.
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