I made sausage and corn chowder the other day. I added both corn starch and Knorr's instant leek soup as thickeners. It simmered over the stove for 25 mins. I thought it may have been too thick, but I resisted the urge to add any more liquids. I let it cool, then took it to work to share. It was reheated in a crockpot at low for several hours and became very soupy or watery. What happened to my chowder?


Unfortunately, cornstarch does that. It does not reheat well. Potato starch is even worse, and that's the thickener in Knorr's Leek Soup.

If you want to reheat something thickened, your best bet is to thicken it with a roux. There are other more modern thickeners (think molecular gastronomy), but I don't know much about those.

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    There are other natural but less-common starches that do pretty well with reheating too - arrowroot is one that can be used without integrating it into a roux. But sticking with a roux may be the best option for flavor alone. – logophobe Nov 14 '14 at 16:12
  • Thanks for your response. Next time I'll have to remember to make a roux. :) – Chi Leung Nov 14 '14 at 16:43
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    @ChiLeung : you can make a roux, and add it to the watery chowder ... although to reduce the chance of lumps, add a few ladles of the chowder to the roux, mix it well, then add that back to the rest of the chowder. – Joe Nov 14 '14 at 17:22
  • @logophobe I've never used arrowroot, but I've always heard that arrowroot is particularly bad about breaking down when heated. – Jolenealaska Nov 14 '14 at 22:17
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    It must be continuous heating. If you add it at the end and cool it, it thickens like no other. You will get jelly in the fridge. However, I do recall that a cornstarch gravy kept on the heat too long will thin. – Swoogan Nov 15 '14 at 5:25

Attention - possible gross information to follow. Queasy fellows stop reading here, please!

Long simmering aside: If some saliva has gotten into your soup (e.g. someone tasting and double-dipping), corn and potatoe starch might break down, too. This is caused by an enzyme (Amylase), that breaks the loger starch down into smaller particles. (see Wikipedia: Amylase) The enzyme stays active; it's not "used up" after splitting some starch, therefore a very small amount of saliva can liquify an entire pot.

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    That's not gross, just very useful information! That said, have you verified by experiment that, say, a double-dipped spoon has this effect in measurable quantities? – Raphael Nov 14 '14 at 16:46
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    [Looking around cautiously] "If I don't taste it, how do I know if it's any good." Thanks for the information. :o – Chi Leung Nov 14 '14 at 16:52
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    Do you know how long it would take to liquify an entire pot, though? – Cascabel Nov 14 '14 at 17:29
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    @Jefromi: No idea how long an entire pot would take, a couple of days perhaps? Oh, and the "activity" of amylase in the saliva differs between humans, that's a genetic trait.(plosone.org/article/info:doi/10.1371/journal.pone.0013352) – Stephie Nov 14 '14 at 18:32
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    I find it very hard to believe that the trace quantities of amylase from the trace quantities of saliva that might make their way into the soup could digest all that starch in only a couple of hours. But here's a simple test: amylase breaks starch down into simple sugars. If whole potatoes' worth of starch had been broken down into sugar, the soup would have tasted ridiculously sweet by the end. Did it? Ridiculously sweet as in "Wait, it said I should add a kilo of potatoes and it tastes like I accidentally added a kilo of sugar instead." – David Richerby Nov 14 '14 at 20:48

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