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The Summer Conundrum… advice sought!

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  • #46
    Are you taking note of the bean temperature before loading them?

    (Just to preface this post... This is merely my opinion based on my knowledge of psychrometrics in the HVAC industry. I'm definitely no expert in the art and behaviour of roasting.)

    I have wondered about the relative humidity, when reading your posts regarding this before, but when the air is heated to such temperatures, the relative humidity would drop so much that it would have a negligible effect on how the beans behave during a roast.

    Generally, more work is required to cool the air with a high relative humidity, as you have to remove the latent heat, too, but the amount of energy required to increase the temperature shouldn't change regardless of the relative humidity. That leaves just the sensible heat difference, which is only 10-20 degrees difference, which is easily achievable by tweaking the gun temperature.

    I don't know how the electronics of the DMM could lag in any noticeable way to have such drastic changes to the roast.

    It's definitely an odd issue. Will be interesting to experience it myself through my first summer.

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    • #47
      For what it's worth, I found a psychrometric chart that goes up to 150°C.

      Let's say that we have an ambient of 11°C with a relative humidity of 60%. At 120°C, in the middle of the drying stage, we'll have a relative humidity of roughly 1%.

      If we look at a temperature of 80°C, pre-drying stage, with the same conditions, we'll have a relative humidity of roughly 2%.

      Regardless of what the relative humidity is at ambient temperatures, it decreases to such a small amount at the temperatures we're dealing with that it would have little to no effect on anything that might be happening during the roast.

      I think I can confidently say that relative humidity can be ruled out as a possible cause to this phenomenon.
      Last edited by dan110024; 16 July 2015, 09:30 PM.

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      • #48
        Originally posted by dan110024 View Post
        Are you taking note of the bean temperature before loading them? …

        I don't know how the electronics of the DMM could lag in any noticeable way to have such drastic changes to the roast.

        It's definitely an odd issue. Will be interesting to experience it myself through my first summer.
        Hey Dan
        Yeah - beans are stored now at a relatively consistent temp in my office now, which has helped some.
        The DMM can read a little high/low in 'extreme' temps (loosing that work loosely - ie sub zero ) but I don't think this accounts for all it - it mainly changes small things like 1C coming on 1-2° earlier etc (which will impact a little in overall timing).
        Humidity is fairly stable out here. I know that some Sydney roasters have had a very different result using my settings - I'm sure humidity and altitude play more of a part then - but we sit about 50% - down there more towards 90%.

        FWIW, I think it is more holistic - a small corretto roaster, large ambient swings (-8° to 40° range) ambient temps impacting the gun, gun internal temps, green bean temps, DMM temps etc - they all contribute towards noticeable 'shift' in flavour throughout the year in Millthope … even when I can fairly well 'match' logged profiles exactly at any time of year through adjusting change temp/TP & ramp temps.

        So I adjust my baseline profile to account for the seasons. Strange but true!
        And what I'm seeing in the cup - if I roast slower in summer, baseline in Spring and Autumn, and then slower again in winter - the roasts seem more consistent!

        Cheers Matt

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        • #49
          With these sorts of variations, you have to remember that using the DMM/Data Logger/Thermocouple hardware that we do, the accuracy tolerance across a wide ambient temperature range will cause a certain amount of 'drift'. Can't be helped when using t/couples combined with simulated cold junction correction in the meter. Improved accuracy across a wide range of ambient conditions could be achieved with more stable measurement technology but I don't really think it's necessary. There are at least a couple of CSers who use RTD100/1000 for their remote temperature monitoring and that's great, but not essential...

          Mal.

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