Friction factor can only be found by doing a trial run. Mix a dough with known temperature for water, flour and room (assuming no preferments) and record final dough temperature. The friction factor is now experimentally determined as the sum of the temperatures of water, flour and room minus 3 times the measured temperature of the dough.

Note that the friction factor depends on your mixer, your ingredients (both amounts and specific ingredients), mixing time, and mixing speed (there may be other smaller influences which we’ll ignore). Thus the friction factor your find using the process above is only valid for that specific case. Having said that, as you do this experiment you will get a feel for the range of friction factors you encounter in your typical setups and you may find it is narrow enough to just always work with the middle.

You should also realize that trying to adjust water temperature so that your final dough will end up at a desired temperature is really most important for production bakers that need a predictable starting point for their fermentation so they can "know" how long it will take (almost exactly) and stay on schedule. For most home bakers this is not necessary and ending up with your dough anywhere in the 70-78F range will work just fine. You will want to ensure things are not too cold to get fermentation started (at an appreciable rate), and not too hot (to either kill the yeast or ferment so fast that flavor does not develop enough). That is another reason why you may be able to just work with a single friction factor as a practical approach although technically it is not right.

 

--dolf

See my My Bread Adventures in pictures