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In this Discussion
After the old forum software breaking in a way that we were unable to fix, we've migrated the site to a new platform.
Some elements aren't working as we'd hoped - some avatars didn't survive the transition, and we're still having issues with attachments that weren't added as inline images, but we're hoping to have that all sorted out soon.
Some elements aren't working as we'd hoped - some avatars didn't survive the transition, and we're still having issues with attachments that weren't added as inline images, but we're hoping to have that all sorted out soon.
Why is it so ?
Alas, the one roasting mystery that eludes me has become a frustrating quest in search for the answer.
It has to do with commercial roasters and why they roast slower when it's hot and faster when it's cold.
Common sense makes you think otherwise, but all my testing and fine tuning of the optimizer on my profiler by using an input variable for ambient temp offset just means I end up chasing my tail in trying to predict and forecast the absolute accurate deviation for temp and time for a given ambient temp and roast batch type.
Whilst that statement did not come out very clear - it's like this..........
I measure the current ambient temp when I am roasting. We have the roaster in an insulated room that is opened for natural ventilation - so it stays relatively constant once we commence roasting.
On warm days - and I consider 25 degrees to be a warm day - the roaster can actually run around 10 seconds longer on batches. This is counter to what your brain should be telling you - the higher ambient means the green beans are warmer before being injected into the roasting chamber, as is the make-up air on the gas burner (although that makes little difference to combustion).
The resultant roast is to specification (level, final temp, etc.) and considerable cuppings at various ambient temps on a batch we run almost daily indicates it makes absolutely zero discernible difference when the roaster runs a few seconds longer on warmer days
On cooler days - say sub-20 degrees, the roaster actually runs faster and can finish anywhere from 1 to 10 seconds earlier. You are literally talking about a few seconds over 15 mins, or 1.1 % deviation.
I am in the habit of making a slight compensation on the profiles because I want it perfect every time.
Where is Professor Julius Sumner-Miller when you need him ?
One theory I have been toying with is the actual rate of change is slowed when it is warmer - that is, the dry-out phase and turning point are reached a little sooner and the roaster "backs off" somewhat, thus slowing the rate rate of temp increase and therefore thermal momentum is effectively slower over set time intervals.
All things being equal it may possibly work in reverse on cold days, with the roaster charging at the roast hard and therefore building up thermal inertia.
Why I am puzzled by this phenomenon is because the roast is never running at full energy for the entire batch cycle - it has heaps of power in reserve and only runs the burner at intervals (more bursts at the early phase, less or not at all in the latter stages). So it's not like it can't cope.
Given that condition, you would think that ambient temp means very little at all because the roaster is controlling the air and bean temp throughout the batch cycle and the outside air cannot affect what is going on inside the drum.
I have thought about the Carnot Cycle and I also wondered about the effects of gas pressure at higher temps affecting adiabatic heating/cooling.
I realize for home roasters the ambient temp plays a larger part in roast batch variation as there are more exposure and less energy being applied. For commercial roasters I would have thought ambient temp would not matter.
One day I will discover the reason.
It has to do with commercial roasters and why they roast slower when it's hot and faster when it's cold.
Common sense makes you think otherwise, but all my testing and fine tuning of the optimizer on my profiler by using an input variable for ambient temp offset just means I end up chasing my tail in trying to predict and forecast the absolute accurate deviation for temp and time for a given ambient temp and roast batch type.
Whilst that statement did not come out very clear - it's like this..........
I measure the current ambient temp when I am roasting. We have the roaster in an insulated room that is opened for natural ventilation - so it stays relatively constant once we commence roasting.
On warm days - and I consider 25 degrees to be a warm day - the roaster can actually run around 10 seconds longer on batches. This is counter to what your brain should be telling you - the higher ambient means the green beans are warmer before being injected into the roasting chamber, as is the make-up air on the gas burner (although that makes little difference to combustion).
The resultant roast is to specification (level, final temp, etc.) and considerable cuppings at various ambient temps on a batch we run almost daily indicates it makes absolutely zero discernible difference when the roaster runs a few seconds longer on warmer days
On cooler days - say sub-20 degrees, the roaster actually runs faster and can finish anywhere from 1 to 10 seconds earlier. You are literally talking about a few seconds over 15 mins, or 1.1 % deviation.
I am in the habit of making a slight compensation on the profiles because I want it perfect every time.
Where is Professor Julius Sumner-Miller when you need him ?
One theory I have been toying with is the actual rate of change is slowed when it is warmer - that is, the dry-out phase and turning point are reached a little sooner and the roaster "backs off" somewhat, thus slowing the rate rate of temp increase and therefore thermal momentum is effectively slower over set time intervals.
All things being equal it may possibly work in reverse on cold days, with the roaster charging at the roast hard and therefore building up thermal inertia.
Why I am puzzled by this phenomenon is because the roast is never running at full energy for the entire batch cycle - it has heaps of power in reserve and only runs the burner at intervals (more bursts at the early phase, less or not at all in the latter stages). So it's not like it can't cope.
Given that condition, you would think that ambient temp means very little at all because the roaster is controlling the air and bean temp throughout the batch cycle and the outside air cannot affect what is going on inside the drum.
I have thought about the Carnot Cycle and I also wondered about the effects of gas pressure at higher temps affecting adiabatic heating/cooling.
I realize for home roasters the ambient temp plays a larger part in roast batch variation as there are more exposure and less energy being applied. For commercial roasters I would have thought ambient temp would not matter.
One day I will discover the reason.
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