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Kitchen Science question- "gravy" thickening, crock potting, etc...

So last night I made some VERY good Colorado/Denver style Green Chile. I like the "gravy" style we make here in Denver as it stays inside a breakfast burrito better.


I've used a dozen different techniques over the years and have never been THRILLED with my resutls but I think I'm close now. I browned and removed my unseasoned, un-floured pork in vegetable oil. I think threw in what I call the Mexican Mirepoix: onions, garlic and finely chopped serrano peppers. I sweated these in the same fat with salt until they had given up some liquid and were beginning to color. Okay.. time to roux it up... I added flour and stirred to mix... I moved this around for a few minutes until I figured the flour taste was gone and then whisked in my hot stock. Classic soup techniques everyone knows, loves, uses and thanks the French for, right? As this thickened I added my green chiles... then my reserved pork... then some other "stuff"... and let it return to barely a simmer and stewed it for just a bit to make sure I had my consistency down correctly. All was good... rich, glossy gravy!

So.. into the crock pot for slow cooking to finish the pork. I let it stew on WARM (not low, not high, just warm) until morning (about 8 hours). The pork was fabulous- fall apart.. but I've lost 50% of my "Graviness"! Much of the fat broke from sauce and was sitting on top.. the gravy had become much more watery...

What happened? How do you keep a roux-based sauce together during long, low, slow cooking? Is it impossible? If not- did I have too much fat to flour ratio? I know I didn't overcook my roux (ie: from cajun food experience I know a dark roux will not thicken nearly as well as a blonde one).

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  1. It is impossible to prevent to my knowledge. The longer a starch like flour is cooked, no matter what color stage it is at when you add liquid, the more the starch proteins break down. That's why a very dark roux does not thicken as well as a light roux as you stated. The same thing happened in your dish because of the length of time the flour cooked even though you did not achieve a dark roux at the beginning. You didn't do anything wrong, you just expected too much. :-)

    In the future you can thicken at the end with a cornstarch slurry or tapioca if you feel the need, but my instincts tell me you already know that. The result will be slightly different as cornstarch and tapioca tend to be glossy and for lack of a better term, thicker and smoother, but it might give you what you want.

    1. You are getting inconsistent results because of the length of time the flour is being cooked. The thickening power of the flour starts breaking down after 4-5 hours. If you want to put in flour early, Cook's Illustrated suggests using tapioca flour instead of wheat flour with a slow cooker.

      Another way you could do it is to thicken the sauce at the end of cooking with a slurry of flour and water or corn starch and water. This gives the advantage of being able to defat the sauce before thickening it. You are cooking pork, there is going to be a lot of fat that probably should be removed.

      I suppose I really should have read Shaw Olivers post before posting my own but I added a tiny bit more info.

      By the way, here is a link to "The Cook's Thesaurus" reference on starch thickeners. http://www.foodsubs.com/ThickenStarch...

      Here is one on all around thickeners. http://www.foodsubs.com/Thicken.html

      4 Replies
      1. re: Hank Hanover

        "I suppose I really should have read Shaw Olivers post..."

        Nope, you explained it much more clearly, I think. :-)

          1. re: Hank Hanover

            Good explanations and resource links. Thanks much! Makes perfect sense.... I suppose I was confused by my knowledge of restaurants that make a chowder and then leave it on a steam table all day... it turns into paste as all the water evaporates and the thickening is compounded... thought my gravy should do the same thing but the crock pot I suppose is *not* a steam table as the temp is probably much higher than the ~200 deg a steam table creates?

            1. re: e_bone

              Crock pot temp isn't that far off but there is a lid to prevent evaporation on a crock pot.

      2. Or use a beurre manie to thicken at the end.

        1 Reply
        1. re: monavano

          You beat me to it. That's what I popped in to say. I've never had it fail, and it is what I think of immediately when I want "gravy" of any sort


          That being said, I also think that the ideas from Shaw Oliver and Hank Hanover are excellent.

        2. The juice from your pork is leaching into your gravy.

          Cook your pork in the original mirepoix and stock. Reduce and thicken with roux at the end.

          1. Wondra flour is good to keep on hand for slurries, since it will not clump when mixed with milk, water, broth, etc., and makes a smooth gravy. If you thicken with cornstarch don't use really high heat to reheat, which will destroy its thickening power. You could also try instant mashed potato flakes, which thicken well and seem to hold better.

            1. "How do you keep a roux-based sauce together during long, low, slow cooking? Is it impossible?"

              *roo* doesn't traditionally go in for long and slow cooking. the true magic of cajun gravy thickness is okra - it's wonderful for long and slow but keep it in muslin so you can fish it out at the end if you don't like it's slimy texture.

              1. I don't use a roux at all in my chile verde. I buy the large packs of corn tortillas, cut them up in three ways - quartered for chips, in strips, and chopped up fine. I put in the chopped up ones while cooking - at least 30 minutes before the end, and that thickens up the chile quite well - not to a glop - but gives it some definition. Then I deep fat fry the strips and chips and serve the chille with the strips. The chips are for apps or the side, along with some guac and salsa. The fried strips gives the chille some heft - even if the chille itself is a little soupy - like crackers. I also add the chopped cilantro and toasted/ground up cumin at about the same time as the chopped tortilla chips - all towards the end - which has nothing to do with thickening, but it's really good!

                1 Reply
                1. re: applehome

                  or just add a masa harina slurry toward the end of cooking.

                2. The problem comes from slow cooking the pork in the sauce. I typically slow cook a six pound shoulder roast in barely enough apple juice to come 1/3 of the way up the side of the meat, but when it has roasted for four to six hours in a slow oven, the liquid will be fully up to the top of the meat!

                  So for your pork, I suggest you do NOT thicken your sauce before slow cooking the pork in it, then thickening afterward. There's just no reliable way of estimating how much thickening agent you need before hand because different roasts (of the same cut) will yield different amounts of liquid. So thicken after. Good luck!

                  7 Replies
                  1. re: Caroline1

                    hello caroline, as i had previously posted, okra would work as a long and slow thickener - i'm guessing the OP wants the gravy to be infused with flavors that develop throughout the entire cooking process as opposed to capturing all the flavor at the end with a roux.

                    1. re: epabella

                      And okra would certainly work as a way to add viscosity to a sauce, but it also adds a flavor of its own that is not the first thing that pops into my mind when I think of a southwestern chile stew. I do use okra in "cajun" (for want of a better word) and Middle Eastern cooking, and it can produce delicious results. But the "texture" of the sauce is quite different. Viscous, as opposed to thickened. Anyway, for a southwestern chile style "gravy" I would go with a buerre manie, as someone else has already suggested, or I might even try dropping some dry torn corn tortillas in a whirling blender to produce a "flour" to use for a thickener in the sauce. With really good corn tortillas this can not only thicken the sauce but give an underscore to the southwestern theme.

                      1. re: Caroline1

                        Rereading the OP I think he wants to stick with flour based thickening as much as possible (the Denver style green chile gravy). I don't know about the 'roux breaking down' with long cooking theory. My guess is that the pork gave up its juices and fat (he did not specify the cut,l did he?). This would have produced the fat floating on top, and a thinner sauce.

                        In this case I'd skim the fat, and adjust the thickening with buerre Manie or the masa slurry. Another option is to cook it a while longer with the lid off to evaporate some of the excess liquid - this may have to be done in a regular pot with more heat than that produced by the crock pot.

                        1. re: paulj

                          Just for the record and not necessarily to split hares or otherwise harm a bunny, pulverizing corn tortillas in a blender and adding them to the sauce is the equivalent of adding a masa slurry without adding extra liquid. You just stir the powdered tortillas into the sauce with a whisk and stir. They will not lump, but they will thicken the sauce. It's the same principle as using crushed gingersnaps to thicken the gravy of saurbraten.

                          1. re: paulj

                            So Paulj that takes us back to the original question (not stated well)... does the quality of flour (roux) as a thickening agent dissapate over time with low heat or did the composition of my stew change and therefore the "thickness" was diluted? In culinary terms: did my sauce 'break"?

                            You may very well be on to something when you discuss the fat rendered into the sauce through slow cooking -I used fairly fatty sirloin chops and therefore perhaps lost consitency because of it.

                            To frame the question and avoid the thread drift- I'm not trying to figure out how to thicken a sauce! I know how to thicken things in a variety of ways. I'm asking about fundamental kitchen science and the thickening qualities of flour based roux.

                            I will most definitely avoid thickening and then stewing in the future but really wanted to understand why it didn't work from the fundamental background of the material properties.

                            As per what transpired... I'm GUESSING that I had both issues in play... flour proteins breaking apart over time and also a breakdown of my roux based on balance: whereas my original suspension was perfect, solid fat was rendered and upset the balance of flour to fat... thus yielding sauce that was overly thin (and the pooling fat on top).

                            1. re: e_bone

                              I'm not sure that the fat to flour ratio is critical in your gravy. As I understand it, the purpose of the fat is to coat the starch particles so that they don't clump when the liquid is added. The individual particles can then absorb the moisture and remain in suspension. Alton Brown has illustrated this in various episodes.

                              Remember that there are other ways of producing this suspension, for example starting with a cold slurry. The slurry approach is used most often with corn starch, but will also work with wheat flour.

                              When you add further fat to the sauce, whether by pouring in oil, or rendering it from the meat, it isn't going to mix with the sauce unless you stir it in.

                              There are sauces that do depend on a fat emulsion, but those don't involve starches (though starch may be added to increase stability). But those do use a roux.

                              1. re: e_bone

                                I think that almost anytime you cook with pork, you are going to have excess fat that will need to be removed which is reason enough to thicken at the end.

                      2. Yes, the problem is the cooking time. The starch granules in the gravy are going to break down over the course of 8 hours. Also, the meat is going to release water into the gravy (remember you are cooking the meat for 8 hours to break down the proteins in it). If using cornstarch at the on of the cooking process is not to your liking (mine neither) what you can do is slow cook the meat in the liquid for 8 hours, then after is cooked, remove the meat from the liquid, make your roux, add the cooking liquid, get the viscosity you want, add back the meat to the thickened liquid and serve. Hope this works.