Desired dough temperature (DDT) is just what is says on the tin. The temperature you want your dough to be. Different temperatures have different effects on the dough. Cooler doughs take longer to ferment and different temperatures favour different kinds of fermentation. Controlling the dough temperature is important a) so that you have some idea of when it will be ready to bake, and b) so that the baked loaf has the flavour and texture you want.
Bigger bakeries than ours employ provers and retarders which are essentially large and expensive temperature controlled cupboards. For us, and for home bakers, the best we can realistically hope for is to get the dough to the right temperature in the first place, and then to keep it there. In his fantastic book 'Bread', Jeffery Hamelman explains how to adjust the temperature of the water in order to acheive the DDT. The difficulty is how to account for the temperatures of the bakery (or your kitchen), the flour, the heat introduced by friction in your mixer and any preferments you are using, all of which can vary by 20 degrees between summer and winter, and different times of day.
Hamelman provides a very simple calculation to work this out (on page 383 in my copy). You first multiply the DDT by 3 (for straight yeasted doughs) or 4 (for doughs including any kind of preferment). You then subtract the temperatures of the air, the flour and the preferment (if you are using one). The remainder is the required water temperature.
I have been using this method for a while, pretty satisfactorily. Recently, though, with the arrival of colder weather, I have found it rather over-estimates the required water temperature and producing to too hot a dough. The reason is quite obvious: the initial multiplication step treats all the ingredients as if they had the same impact on the dough temperature, but they do not. For example, one might use twice as much flour as preferment.
So here's my contribution - a means of taking different ingredient quantities into account, whilst still being able to do the calculation on the back of a baking schedule.
First, one must estimate the relative number of parts of the ingredients which will contribute to the overall dough temperature. One might use 400g of flour, 300g of water and 200g of leaven for example: 4 parts flour 3 parts water, 2 parts leaven. Add all of these together to make 9 parts for the whole, and add one for the air temperature, making ten parts in all. We then multiply the DDT by the number of parts, so if we wish for 24C we have 24x10=240. We now take the temperature of each ingredient, and multiply it by the number of parts for that ingredient. If the temperature of the flour is 17C we do 17x4=68, and if the air temp is 15 we do 1x15=15. We then subtract each of these products from the multiplied DDT, i.e. 240-68-15 etc. This remainder must be accounted for by the water - but we have three parts of water, so we divide by three to get the actual water temperature. If the remainder was 120, we would do 120/3=40, and then use water at 40C. The original calculation produces a water temp of 46C.
To work it all out, I draw up a table like this:
Ingredient Parts Temp
---------------------------------------------------------------
Dough 10 x 24 = 240
---------------------------------------------------------------
Air 1 x 15 = 15
Flour 4 x 17 = 68
Starter 2 x 18 = 36
SUM:119
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Water 3 x 40 = 121
I start by determining the 'Parts' column, then multiply the DDT, and then take the temperatures in the middle rows. Lastly, I do the multiplications, subtraction, and the division to get the water temp. This method takes a little longer to work out, but so has so far produced much more satisfactory water temperatures.
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