Flour and corn starch can be fightin’ words in canning circles and are generally taken to be a dividing line between safe and unsafe canners.
- 1 It’s fine to use flour and corn starch in modern canning recipes
- 2 What is the danger of using flour and corn starch in home canning?
- 3 Starch in home-canned soups
- 4 Exceptions to the “no thickener” rule
- 5 Note for celiacs
- 6 The anti-flour vigilantes
It’s fine to use flour and corn starch in modern canning recipes
It’s fine to use flour and corn starch as thickener when modern, tested recipes from reputable sources call for it. These recipes have been lab-tested to ensure their safety. Don’t use old recipes of unknown origin that call for it, and don’t ever add it yourself willy-nilly to canning recipes.
The flour meant will be plain (or all-purpose) white wheat flour — as in, not whole-wheat flour or flour from any other type of grain. And do NOT use self-rising flour.
What is the danger of using flour and corn starch in home canning?
There’s a general caution about their broad use for two reasons:
- They can thicken food products too much, too quickly, causing density issues — code for “interfering with even heat sterilization throughout the whole product”;
- They doesn’t always perform great in all products, anyway: in things such as canned pie fillings, they can clump.
Penn State Extension says,
Adding flour or other thickening agents to a product for home canning prevents the heat from penetrating to the center of the jar, interfering with safe processing to destroy the bacterial spores that cause botulism. Never add thickening agents to a home canned product. Wait until you are ready to prepare the food for serving and then add the flour, cornstarch, or other thickening agent you are using.”  Making Soup Safely. Penn State Extension. 22 October 2012 blog posting. Accessed March 2015 at https://extension.psu.edu/food/preservation/news/2012/making-soup-safely
Even back in 1948, the Kerr Canning company was warning against flour in canning:
Should steak, chicken or other meats be rolled in flour for canning? No. Flour retards heat penetration, flakes off in bottom of jar and gives the meat or chicken a slightly warmed-over taste.”  Answers to your canning questions. Kerr. Question 95, page 52. 1948. Accessed March 2015 at https://www.endtimesreport.com/5-Kerr_1948_Canning_Questions_and_Answers.pdf
The prohibition against thickener is enforced by anti-thickener vigilantes, who are a subset of the Safe Canning Police.
Starch in home-canned soups
No tested soup recipes for home canning that we know of currently allow for addition of a flour or cornstarch ingredient.
That means no noodles, dumplings, pasta, matzoh balls, flour or Clearjel thickener, rice, grains, etc. Not even if they are whole grain, hand-harvested, organic, or are gluten or GMO or whatever free!
Products high in starch also interfere with heat processing. Thus, add noodles or any type of pasta, rice, or dumplings to canned soups or stews at serving time. Avoid using noodles, alphabet noodles, spaghetti, or other pasta, rice, barley, etc to canned soups.” Penn State Extension Service. Making Soup Safely. 22 October 2012. Accessed August 2017 at https://extension.psu.edu/food/preservation/news/2012/making-soup-safely
The exception is three “starchy” vegetables: potatoes, corn and peas. You will see those in some home-canned soup recipes.
Thicken your soup as desired upon opening. DIY SOS Mix makes for an amazing instant thickener.
Exceptions to the “no thickener” rule
Penn State Extension goes on to say, from the initial quote mentioned above, something very important which anti-thickener vigilantes try to sweep under a rug:
The only exception to this rule is when a scientifically research tested recipe calls for Clear Jel® as in pie fillings or small amounts of thickener in a few relish recipes. It is not safe to just add starch to any recipe or to create your own recipe.”  Making Soup Safely. Penn State Extension. 22 October 2012 blog posting. Accessed March 2015 at https://extension.psu.edu/food/preservation/news/2012/making-soup-safely
So while reminding people that they can’t just add thickener to any old canning recipe, Penn State is acknowledging that the use of thickener is fine when a tested recipe calls for it.
Here are a list of tested recipes as of 2015 where flour and corn starch are used:
Asian-style hot sauce. Calls for 2 tablespoons of flour.
Mustard pickle. Calls for ½ cup of flour . Ball Blue Book. (Page 50 0f 36th edition; page 80 of 37th edition.)
Pickled Corn Relish. USDA. They say you may use flour to thicken the relish. The quantity indicated (4 tablespoons) works out to be ⅔ teaspoon per cup. That’s pretty insignificant. And it’s easy to see why you might want to exercise the option and use it: the relish can be very soupy without it.  United States Department of Agriculture (USDA). Complete guide to home canning. Agriculture information bulletin No. 539. 2015. Page 6-28.
Bernardin Guide 2013 has the following recipes: Chunky Mustard Pickles page 75, Mustard Beans page 75, Marrow ‘n Onion Mustard Pickles page 75, Fennel Relish page 76, Homestyle Corn Relish page 76 (Flour, or ClearJel)
- Corn Relish (Quick). Canadian Living Test Kitchen. The Complete Book of Preserving. Montreal, Canada: Transcontinental Books. 2012. Page 183.
- Corn Relish. Canadian Living Test Kitchen. The Complete Book of Preserving. Montreal, Canada: Transcontinental Books. 2012. Page 184.
- Lady Ross Relish. Canadian Living Test Kitchen. The Complete Book of Preserving. Montreal, Canada: Transcontinental Books. 2012. Page 177.
- Thousand Island Relish. Canadian Living Test Kitchen. The Complete Book of Preserving. Montreal, Canada: Transcontinental Books. 2012. Page 178.
- Zucchini Mustard Pickle (Small Batch). Canadian Living Test Kitchen. The Complete Book of Preserving. Montreal, Canada: Transcontinental Books. 2012. Page 173.
- Green Tomato Relish. USDA.  United States Department of Agriculture (USDA). Complete guide to home canning. Agriculture information bulletin No. 539. 2015. Page 6-29.
- Zucchini Relish, two recipes. Page 3 of: Harris, Judy. Zucchini Recipes. Davis County Extension: Utah State University Extension.
- Zippy Zucchini Relish. Canadian Living Test Kitchen. The Complete Book of Preserving. Montreal, Canada: Transcontinental Books. 2012. Page 170.
- Zippy Pepper Relish. Canadian Living Test Kitchen. The Complete Book of Preserving. Montreal, Canada: Transcontinental Books. 2012. Page 172.
Replacement with Clearjel
The Ball / Bernardin Complete Book (2015 edition) appears to be moving its recipes that called for flour and cornstarch to using Clearjel instead.
The Bernardin 2013 guide offers one recipe where you can use either flour or Clearjel. ( Homestyle Corn Relish page 76.)
Note, though, that canning authorities advise us not to swap flour and cornstarch in recipes for Clearjel of our own volition: they advise us to only use Clearjel where a tested recipe calls for it, and stick with using the flour and cornstarch where the tested recipes tells you to.
Note for celiacs
The above recipes from Ball / Bernardin Complete, and Bernardin, can allow you to enjoy these thickened home canned products using recipes tested for Clearjel.
As always, though, just verify with your source of Clearjel. The makers of Clearjel certify that it’s free from gluten, but it’s possible some cross-contamination with wheat flour gluten could occur in the hands of those who buy it in large quantities and repackage it into smaller packages for sale to home canners.
The anti-flour vigilantes
In the category of “a little knowledge is a dangerous thing”, the anti-thickener vigilantes unfortunately have interpreted the flour situation to be an absolute, universal ban on it. They even discount the recommendations of the reputable authorities who have actual certified lab expertise in this field.
The reason could be that the vigilantes only feel comfortable in a black and white world, where things are either allowed or not allowed, and their thinking was never fully developed enough to leave room for anything in between.
These vigilantes don’t want people even to know about the lab-tested recipes above where thickener is authorized. People have been kicked immediately out of canning groups just for mentioning them, as though the very titles of those recipes are part of some Index Librorum Prohibitorum in the Church.
Ignore the vigilantes on this topic.
To be clear, do not go adding thickeners of your own accord willy-nilly to canning recipes, and do not use old family canning recipes that might call for thickeners. But when a trusted, reputable authority does call for such a thickener in a modern canning recipe, use it with confidence — and exult in the rare occasion where you do get to use it!
|↑1||Making Soup Safely. Penn State Extension. 22 October 2012 blog posting. Accessed March 2015 at https://extension.psu.edu/food/preservation/news/2012/making-soup-safely|
|↑2||Answers to your canning questions. Kerr. Question 95, page 52. 1948. Accessed March 2015 at https://www.endtimesreport.com/5-Kerr_1948_Canning_Questions_and_Answers.pdf|
|↑3||Penn State Extension Service. Making Soup Safely. 22 October 2012. Accessed August 2017 at https://extension.psu.edu/food/preservation/news/2012/making-soup-safely|
|↑4||Making Soup Safely. Penn State Extension. 22 October 2012 blog posting. Accessed March 2015 at https://extension.psu.edu/food/preservation/news/2012/making-soup-safely|
|↑5||United States Department of Agriculture (USDA). Complete guide to home canning. Agriculture information bulletin No. 539. 2015. Page 6-28.|
|↑6||United States Department of Agriculture (USDA). Complete guide to home canning. Agriculture information bulletin No. 539. 2015. Page 6-29.|
Hi I am canning cooked taco meat and I used taco seasoning that has corn starch as the second ingredient. Is this going to be too much corn starch?. I added beef broth so it was soupy mix. Should I plan on not using this canned meat?
I would like to add bouillon powder (1 tsp) to a quart size jar when hot packing chicken. Many bouillon powders contain corn starch, some listing it as their second ingredient. Is that small of a quantity an issue?
The minute quantity of corn starch isn’t going to be an issue. If it were, extension agents wouldn’t have been giving the nod to broth cubes for generations.
I will take your advice and not thicken my apple pie filling until I get ready to use it. It is my understanding that you don’t need to pressure can apple pie filling that a hot water bath is enough. Any thoughts on this?
Yes, a hot water bath is perfect. You could probably use the canning times for apple slices.
Can you thicker strawberrinf with corn starch when canning
Cornstarch is no longer recommended in home canning as there were too many complaints overall over the years about its performance. On top of that, there were concerns about the density — about tiny nasties using clumps of starch to hide in from the heat, and survive the canning process. Thicken when you open the jar instead. Or, if you want to make a strawberry pie filling, there is one you can make using Clearjel (https://www.healthycanning.com/strawberry-pie-filling) , which is a form of cornstarch that has been tested safe for a few home canning applications.
If you used a recipe from pillsbury,and it has 2tablespoons of all purpose flour in it when making apple pie filling is it safe everything I’m reading says no I used a water bath canner on pressure 10 for 25 minutes or is it all bad?
Hi Barb, what you did sounds a bit complex. I’m going to suggest you check with these Master Food Preservers. https://www.facebook.com/UCCE-Master-Food-Preservers-of-El-Dorado-County-456649991034665/
Hello. I used one cup of cornstarch while making quart size jars of Apple pie filling in 2017. I opened my first jar a couple of months ago, April 2019 to make apple crisp and no one in my family got sick. My question is. Would you recommend I discard the rest of the jars that I have in my cellar.
Hi Barbara, ask one of these Master Food Preserver groups what they feel.
Hello I have a recipe for Corn Relish and it calls for a little flour now I am having second taught can I use it or just leave it and not add it I don t want my Relish to be to watery either can you give me any ideas on this little issue of mine ….
Thank you have a nice day
There are several modern tested recipes that call for a little flour and they are absolutely fine to use because they have been tested to ensure that the density is safe with the flour. Here are two examples: this one from the National Center for Home Food Preservation, https://nchfp.uga.edu/how/can_06/pickled_corn_relish.html and this one from Bernardin. https://www.healthycanning.com/sweet-corn-relish/.
You could also check Canadian Living — their canning recipes are tested and therefore trustworthy. They’ve got a corn relish recipe, lightly thickened with flour, on page 164 of their home preserving book. https://www.healthycanning.com/canadian-living-as-a-safe-canning-recipe-source/
I’d suggest you find the modern version that is closest to the one you want to make, and make that. It’s safe to tweak the dry seasonings (spices, dried herbs) if desired to make the taste of the modern version resemble your recipe. Don’t change quantities of vinegar or veg. Hope that helps.
Wanting to can matza ball soup (small to med size balls) but am getting mixed information and since the matza ball is where the grain is vs using it as a thickening agent I am kinda confused. Any help or advice would be greatly appreciated.
If you go to reputable sources, there really isn’t any mixed information on this — they’re pretty clear. No dumplings, noodles or pasta. There’s a difference between light thickening, and big lumps of starch. The issue is density. The concern is that large collections of starch molecules could be used as safe harbour by botulism spores to help insulate themselves from the heat of pressure canning. You’ll note as well that whenever thickening is used, it’s in an acidic recipe, where the acidity helps prevent botulism spores from germinating anyway. See: problem ingredients section here: https://extension.psu.edu/food/preservation/news/2012/making-soup-safely
Add your matzoh at time of serving. Or, if you really want it in the soup, then freeze the soup.
Hope that helps.
Magno San Gabriel
I want to start my food pprocessing business, My question is, how come that no thickening ingridients on making tomatoe catsup? But in a commercial tomatoe catsup it was noted. Like corn starch.