Why won't my sauce thicken?

Are you dissolving the starch in cold water first?
Are you pouring the starch into a high acid sauce??
Are you blending the starch in well(stirring while adding)?
Liquid added 1 cup to 1 T starch, if this be for dissolving purposes, It's to much.

All cornstarch and arrowroot congeal after refrigerating.:smiles:

Could you describe how you add the cornstarch, how hot the "liquid" is when you add it, and whether you continue to cook the liquid after adding the cornstarch?

Corn starch can be a little tricky with acidic foods, but peaches aren't that acid and you're getting plenty of structure once the starch has had the opportunity to fully dissolve and mix with the ingredients. At first blush it does seem as though the problem is failure to provide the opportunity adequately. But I'd like to know more before opining.

BDL

Potato starch seems to be more forgiving than cornstarch, so in the interim, you could switch to that if you can't figure out the current problem.

Totally different applications for both.

True. I could be wrong, though I use them much the same way [granted, it's in (specifically Asian) cooking rather than baking].

1 tablespoon per cup of liquid seems a bit light so that could be part of the problem. I usually use about twice that in cobblers with good results. Also, are you letting the mixture actually boil, or just simmer? In my experience, if you're not seeing actual bubbles it never really thickens.

That's one of the lines I was thinking along. So a hearty "+1."

The other "threshold" technique question, was whether the OP was adding the starch already well dissolved in a slurry, or was doing it in some other way.

It seemed like a good idea a couple of hours ago to let the OP give a fuller description of the process before making suggestions, but in retrospect that feels artificial. Whatevvah.

Corn starch isn't what you'd call tricky but there is a right way to do it. It should be thoroughly mixed into liquid and allowed to stand for a couple of minutes, then mixed again before adding to hot, preferably boiling liquid. The slurry should be mixed in completely. As soon as the liquid starts to thicken, the temperature should be reduced.

In the same way corn starch won't reach its thickening potential quickly at less than a boil, it will break down if it's overcooked. So you do want it to boil, but only for a couple of minutes at most -- and it's best added when the liquid to be thickened is already at a boil in order to control the situation.

It's a good idea to make twice as much slurry as you'll think you need, and if the first half doesn't give you the thickening you want after a minute or so, add half the remainder, then if that doesn't do the trick, add the rest.

Cornstarch has roughly twice the thickening power of flour. My thoughts for cobbler are roughly 1-1/2 to 2 tsp cornstarch per cup of "gravy." 1 tbs doesn't seem like way too much, but 2 tbs does -- at least to me.

Another excellent thickener for cooked fruit is tapioca. It takes longer and is trickier to judge -- but you get such a nice gloss.

BDL

You can get a nice finish gloss with that schmancy French techique as well. I think it's called a liason finale.

\This was usualy made from eggs and used to enrich soups and some sauces. Very rarely done anymore because of salmonella fears.:chef:

Which can be overcome with pasteurized eggs(or a working knowledge of the mathematical odds of actually getting sick from eggs).

I was just thinking about swirling a pat of butter in at the end to tighten the sauce and give it some sheen. :)

That's monter au beurre.

Enrichment with eggs is fine for soups, though, because once the eggs have been tempered you can get them pretty hot without scrambling. Cobbler? Maybe not so much.