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Calculating DTR

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  • Calculating DTR

    There has been some discussions online regarding Roast Development Time (DT) and suggestions that it should be considered in terms of a ratio of total Roast time (DTR), (as apposed to say targeting around 3 mins only), and that trying to target a ratio for DTR of between 20%-25% appears to produce good results in the cup. This seems to work for the way I roast, and I believe it has improved my roasting. This may of course not suit everyone, and would depend on your ultimate target requirements etc. so please take that into consideration.

    I have attached the following Excel Workbook (zipped) in case anyone finds it useful for determining a Target DTR based on the First Crack Time. Set the First Crack Time Minutes and Seconds using the scroll bars and it will calculate a set of DTR %s and Drop Time within the range.

    In case you find it useful.

    Comments welcome.

    Attached Files

  • #2
    This is a great little tool, Thanks Graham Very easy to understand and use


    • #3
      This is based on the observations by Scott Rao is it Graham?



      • #4
        Hi Mal,

        I'll let Graham answer your question but throw in my own $0.02.....

        One of the important things to take away from Rao's book is a sentence in the foreword.

        Paraphrasing ( as I sold my copy.... nothin' in it worth keeping ) he says that by writing the book he hopes

        to start a conversation of better roasting technique; I think that the rest of his book should be viewed from this perspective.

        As with Graham, my roasts ( commercial drum) were already fitting in with Rao's TDR observations but it should not lead one to

        the conclusion that there is a 'one size fits all' thing going on. Experimentation is key in the development of

        anyone's roasting journey.

        Currently, I am manipulating the 'drying time' heat curve dynamics of my roast profiles and have been amazed at what is happening 'in the cup'.

        The book also reveals Rao's bias towards equipment, so take his vulnerability into account too.

        An interesting discussion on CS might be seeing how the TDR of 20-25% fits in with a corretto or popper set up, both of which can

        produce excellent results.

        In Rao's desire to 'start a conversation' he fails to discuss how manipulating the TDR can affect sugar, acid and body development and ultimately

        the balance, flavour and mouthfeel of any one bean, or how to use TDR to bring out the best in beans that don't work according to plan.


        • #5
          Hi chaps and thanks for the comments,

          I have not read Scott Rao's book, but I did read an article he wrote which is obviously in the book as well. I probably deliberately avoided getting into the why's and wherefores' of the theory, because as Chokkie has noted there are lots of aspects that are needed to be taken into account, and like all recommendations while I have used the formula, it is only as a starting point for experimentation, which did help me, so offered the spreadsheet just in case someone else finds it useful.

          I have never used a Popper or Corretto and I am not sure if the DTR calculation holds true for them as well, but if anyone wants to experiment, then I though this could be useful, not only from the perspective of the theory but also from a perspective of consistency.

          I would be interested in seeing if anyone makes use of it and if it makes any difference to their roasting.

          As Chokkie notes, it's a set of parameters that can be used for your roasting journey (I must be watching too much reality TV :-) ) rather than a set of rules to follow slavishly.



          • #6
            I see the TDR as being a bit like a roaster's version of grind, dose and tamp......

            If your core technique is on the money then you can go experimenting as much as you like, 'cos you always know where home is.

            I think your tool will be a great asset for the CS roasting community.


            • #7
              For what it's worth Chokki'...

              My views of Scott Rao's various published observations and promoted views, very much mirror your own. I was just curious if that was where Graham had come across the TDR measuring stick.

              The only rules I've ever followed with regard to my home roasting, are those that my palate tells me are good, or bad. Like you say, it might be interesting to see if the TDR regime (or a variation thereof) applies to the various home roasting methods used by CSers. I'll leave that for others to explore though, as I'm happy sticking to what I know works for me (over many years of experimentation) as I don't have that many hours left in a day (these days) to do any more experimentation of any substantive involvement.

              Would be interesting to see what others may be able to discover though....



              • #8
                Roast Designer V3

                I got talked into expanding my original DTR calculation into a more fully fledged Roast Designer based on providing the ROR for the Drying Phase and the ROR for the Maillard Phase and either feeding that into the DTR calculations or just using the DTR calculation as originally envisaged. I also gave it a User Interface that's is more descriptive (or possibly over the top even), so that its usage is self explanatory.

                This obviously does not take into account a number of the other variables that cannot easily be accounted for, and also should be viewed as an aid to setting up some of the roasting parameters that you may be already be taking into account. Common sense and sensory methods will still be needed.

                But if you are curious and maybe find it useful I have attached it here.

                As usual comments/feedback welcome, especially in terms of the calculations, which may ultimately require some tweaking.

                Note: I can organise a Flash version if there is enough demand.

                Roast Designer V3 attached in zip format.

                Attached Files


                • #9
                  Very nice work Graham....



                  • #10
                    I have attached a Flash version to this post for those that prefer not to use Excel. Its also a less cluttered interface.

                    Just double click the file and it should start in a browser providing you have Flash installed. Resize the browser as required.

                    Attached Files
                    Last edited by GrahamK; 10 January 2015, 10:28 AM.


                    • #11
                      Hi Graham

                      Thanks for the flash version. I use LibreOffice or OpenOffice Calc and on those there are no scroll bars or means visible to edit the values.
                      The Flash version is also much better layed out and seems to work.



                      • #12
                        No problem. I just loaded it on another PC and some of the static text has not fitted as well and has scroll bars. Could be dependant on the browser. I replaced it with a new version (v3.2) in the post.

                        Last edited by GrahamK; 10 January 2015, 10:29 AM.


                        • #13
                          Roast Designer V4

                          Latest V4 (Flash) -

                          - Also allows the use of Fahrenheit inputs
                          - 2 files now provided - call the .html file to standardise the frame it runs in
                          - Some of the setting limits were incorrect

                          Attached Files