corn starch thickened sauces

[augustiner]

i just made a chow mein style stir fry, and i thickened the sauce with a corn starch slurry. while i was eating it, the sauce relaxed and because a thin, runny liquid again. this has happened before, most notably when i've made mapo tofu. i had reasoned that maybe the excess water in the tofu cubes released after cooking and thinned the sauce out. but i don't know. has anyone else had a similar problem? are there more reliable thickening starches? i've used potato starch before, and can't remember if i had trouble with the sauce breaking, which probably means it didn't.

[Val]

I've been using a fabulous recipe for mapo tofu from this board from a poster named mabziegurl (don't think she still posts but her mother was Chinese, she said) and it does NOT use any thickener...just wondering if you'd like to try it???

[augustiner]

no thank you, i like how the thickened sauce binds the mild tofu and super flavorful meat together, as well as how it coats rice. if there is an issue with my mapo tofu, it must be excess water that i don't properly deal with. i also like softer tofu, but that can't be it, since i've had tasty mapo tofu made with soft (not silken or korean sundubu style tofu) in restaurants with properly thickened sauces. not gloopy, but rich and...gently binding.

[ipsedixit]

Can you tell us how you made the corn starch slurry and how exactly you incorporated it into your sauce?

Somethings to keep in mind.

- Always mix a slurry of cornstarch and a small amount of cold liquid (water, stock, wine, etc.) until smooth, then add this mixture, slowly, to the food that you want thickened. Key here is "slowly".

- Sauces thickened with cornstarch will thin if cooked too long, boiled or stirred too vigorously. Key here is "too long" ... you need the sauce to boil in order to incorporate the slurry, but just not too long.

- So, adhering to the point above, stir gently and cook for no more than a minute over medium heat after the sauce has thickened.

- A higher proportion of sugar or a particularly high proportion of fat in a mixture can also cause a cornstarch sauce to break, or thin. To remedy, try adding more liquid.

- Lemon juice and other acidic ingredients can also reduce the thickening power of cornstarch.

[augustiner]

i mixed roughly 1/2 cornstarch to 1 part cold water, by sight. the sauce thickened fine poured at the end, at the hard boil, and only broke about 5 minutes after i took it off the stove. i didn't add any sugar to the sauce, except the small amount present in the oyster sauce i added (to the chow mein sauce, not the mapo tofu sauce). it wasn't very fatty, either (it was just a bit of duck broth, oyster sauce, sherry, soy sauce, and a touch of sesame oil). but these are good tips, i'll pay more attention the next time i do a starch-thickened stiry fry and hopefully figure it out!

should i be adding more slurry?

[goodhealthgourmet]

"the sauce thickened fine poured at the end, at the hard boil,"
~~~~~~~
there's your answer. boiling breaks down the starch granules so they become leaky. don't boil it next time :)

[ipsedixit]

Bingo!

[goodhealthgourmet]

2 potential causes - the temperature was too high, or, as you suspected, the tofu exuded water.

don't try arrowroot - it's more likely to break at high temperatures, and cornstarch really is the most powerful and stable of the common thickeners. don't keep it over high heat for too long, and try using extra-firm tofu and weighting it for a while before using to press out excess moisture.

[L987]

see if u find something that r specially made for thickening sauces.. where i live we have one for light sauces and one for dark, u just sprinkle it on the sauce and stir, u dont need to mix it with water or anything

[monku]

You could try arrowroot, but maybe the tofu was the culprit and would be again.