HOW TO MAKE STARCH SLURRIES
The topic of using starch as a thickening ingredient in liquid dishes have been brought up already in our article on roux. That time, the flour was pre-treated, so to speak, in butter or other fat, giving different tastes and colors. However, starch, and now I mean pure starch and not flour, can be used on its own as a thickening agent. It is very effective and quick, and has been used in cuisine since ages. The little problem that can arise with pure starches however is that they can break down fairly quickly - in other words, serve the dish as soon as possible! Pure starch also has an advantage over roux in that it doesn't color the dish (of course, in some cases, the opposite can be desirable, and that's where roux can enter the field).
Pure starch can be found in potato starch or rice flour/starch, as well as in cornstarch. Also, arrowrot or tapioca are good for making pure starch slurries. The best thickening ability is found in potato starch, followed by tapioca. The other starches are less powerful thickeners, so bear that in mind when substituting the starches in your recipes. In general you need three times as much rice flour as potato starch. Or:
The proportions are 3:2,5:2:1 for rice flour:arrowroot or cornstarch:tapioca:potato flour.
The way of using starch slurries is simple: disperse the starch in a cold liquid first (prior to blending them with the dish) so that there are no lumps and so that you get a fairly thick liquid. You can make the slurry in advance if you wish, but you need to remix the starch since it has a tendency to quickly gravitate towards the bottom of the bowl. It is important to do so in order to have an evenly mixed slurry. Starch doesn't dissolve very much in water so you can never prepare a homogenous slurry that stands tall for hours.
When you are ready to add the slurry to the dish, remember to take it off the stove first. Do not add it into a boiling liquid, it is better to have some simmering state in your pot!
When adding the starch slurry into the hot liquid, make sure to stir continuously. This is necessary since you want to distribute the starch quickly and evenly within the hot liquid. Now, observe how the liquid becomes thickened within seconds. Whenever you feel that you got the desired thickness, just stop adding more slurry. However, don't stop the stirring because some lumps may form or the starch may fall to the bottom and start to get scorched. Then bring the liquid back on the hot oven and cook until the liquid has thickened and becomes clear.
When finished, bear in mind that the thickened sauce/soup/stew or whatever you've prepared will not hold its thickness forever. That's the weak point of pure starch slurries. The simplest is of course to serve the dish right away, but if you can't, maybe you can reheat the dish before serving and add the starch in there just before you serve it.