Miche wrote:

> In article >,
> Bob Pastorio > wrote:
>
>
>>Melba's Jammin' wrote:
>>
>>
>>>How do the thickening powers of, say, cornstarch, arrowroot, and flour
>>>differ? Not what the outcome looks like or how it keeps, but how they
>>>relate in thickening power. I.e., if it takes 1 tbsp of flour to
>>>thicken x amount of liquid, it will take how much arrowroot to produce
>>>the same thickness in the same amount of liquid?
>>
>>flour (as roux)= 2 tablespoons to 1 1/4 to 1 1/2 cups liquid
>>potato starch= 1 tablespoon per cup liquid
>>tapioca starch= 1 tablespoon per cup liquid
>>cornstarch= 1 tablespoon to 1 1/2 to 2 cups liquid
>>arrowroot= 1 tablespoon to 2 cups liquid
>>
>>They don't all have the same effects. Potato starch will be more
>>opaque than the rest, but it will thin out with boiling. Tapioca
>>starch will become stringy if not handled properly. Arrowroot will be
>>the shiniest.
>
>
> Arrowroot thins out again on standing. It needs to be added right
> before serving.

I don't agree. It will thin if held on heat for a protracted period or
if overwhisked because of the stress ("sheer") on starch strings.
Otherwise, it works as well as any starch and better than most.

If you want the technical stuff, start here for how the starch is
tested. <http://www.starch.dk/isi/methods/19brabenderNotes.htm>

Here are some definitions:
Pasting temperature The temperature at which the viscosity curve
produced in the Brabender viscograph leaves the baseline as the
temperature rises during the initial heating process. Care is needed
in using this term as other definitions exist.

Peak viscosity The highest viscosity reached during the gelatinisation
of starch usually corresponding to the point where all the granules
are swollen to occupy a high proportion of the available volume with
each in contact with its immediate neighbours. May be conveniently
observed on the Brabender Viscograph. Note that on cooling the starch
paste, the viscosity may rise above this level, but only the initial
shoulder (Corn starch) or true peak (Potato starch) values determined
on the hot paste are termed peak viscosity.

Here are the characteristics of arrowroot.
<http://www.starch.dk/isi/starch/arrowroot.htm>

The black line is when and how hot the "cook" is. The red line tells
you how thick it is over time. That it thins slightly with long
cooking, but thickens upon cooling.

Pastorio