Thickeners for Home Canning

It is the time of the year for callers to be canning pie fillings. Callers want to can a filling that can go straight from the canning jar into the pie. That is not always possible since the only recommended thickener for pie fillings is a product called Clear Jel. This product is not readily available in stores like so many other canning products. At the time researchers were developing pie filling recipes, they anticipated that Clear Jel would be sold alongside other canning supplies. At this time, the easiest way to purchase Clear Jel is on the internet. It is very difficult to find Clear Jel at a local store.

Callers often wonder why Clear Jel is the only recommended thickener. Not all starches perform the same way; Clear Jel can be heated and cooled several times and still maintain the same thickening power. Cornstarch used to thicken pie filling can form clumps and cause the cloudiness inside the jar. Pie filling made with cornstarch may not thicken while the pie is baking.

It can be tempting to just experiment with adding a bit of flour or cornstarch to your recipe but the National Center for Home Food Preservation tells us that it is a bad idea. Here is their explanation.

“In general, you are correct — it is NOT safe to add flour/corn flour or any other thickening agents to just any canning recipe. Thickening agents slow the ability of heat to penetrate throughout the product. Heat must be distributed evenly and at a high enough temperature in order to destroy mold, yeast, and bacteria. In low-acid foods (vegetables and meats for example), there is a risk of causing botulism if the product is not heated properly in the canner. Adding a thickener to a tested recipe and then processing it for the same amount of time as tested without a thickener would risk under-processing of that product, and in turn, would risk causing food poisoning/spoilage.”

There are a couple of recipes that do include flour on the National Center for Home Food Preservation website. “In the particular case of the Pickled Corn Relish, the recipe was tested with the flour paste thickener as part of the ingredients and approved by the thermal process authority providing that recipe. That is why we can recommend adding this particular flour paste to this particular recipe. As you can see from looking over the ingredients list, there is a large portion of vinegar in this recipe, which does play an important role in the safety of pickled foods and does also influence the margin of safety for adding the thickening agent. There also is not that much thickening that occurs; the resulting brine in this product is still quite watery, so it’s not excessive thickening. The amount recommended should not be increased, however, and it should be incorporated just as described. We do not know the effects of adding the same flour paste to other recipes, however, so we would not recommend using it in other canning recipes.’

Please resist the temptation to add a thickener not listed in a recipe. Keep your family safe. You can always easily thicken canned apples or other fruits for use in a pie.  You may see some new thickeners on the market but for now, Clear Jel is the only recommended thickener for use in pie fillings.

 

 

Liz Meimann

Liz Meimann

I received both my undergraduate and graduate degrees in Food Science at Iowa State University. I love to quilt, sew, cook, and bake. I spent many years gardening, canning, and preserving food for my family when my children were at home.

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29 thoughts on “Thickeners for Home Canning

  1. Hi Barb, for apple pie for the freezer, you can use wheat flour, corn starch, or tapioca. Just remember to use a bit more thickener as pies that have been frozen before baking tend to be a bit jucier than those that have not been frozen. Use twice as much flour as corn starch. It is hard to give an exact amount without knowing how many apples or size of pie pan. I’d refer to a trusted cook book for exact amounts.

  2. If you are using the recipe for apple pie filling for canning (using Clear Jel) you can use the same recipe then freeze it. Just make sure there is enough head space because it will expand as it freezes.

  3. If a recipe calls for cornstarch and I want to can the filling for use later, can I replace the cornstarch with an equal amount of Clear Jel?

  4. The general rule is that you can substitute Clear-jel for corn starch using the same measurement. Clear-jel thickens when cooked and then does not thicken much more when cooled. Cornstarch continues to thicken some after it cools. Here is the website for OSU research based food preservation information. If you go to fruits and vegetables you will find a handout SP 50-616 Fruit Pie Fillings that gives recipes for many kinds of pie fillings that are tested for canning. .http://extension.oregonstate.edu/fch/food-preservation. Glad you are considering Clear-jel for filling.

  5. Carolyn, As you may know, there are two types of Clear Jel®, “instant” and “regular.” “Instant” does not require heat to thicken. The product will thicken once the liquid is added; it is meant for thickening things that won’t be cooked. “Regular” is the preferred type to used for canning as it must be heated to thicken and will withstand heat needed for processing. “Instant” can be heated once, but it does not do well beyond that. “Instant”, therefore, is unsuitable for home-canned fillings, but it would be okay for pie fillings that will be frozen instead of being canned.

  6. If I wanted to can a beef stew, could clear gel or any other thickening agent be used?

  7. Meghan, if you are making beef stew to eat immediately, you could use any thickening agent of choice. If you are asking about using clear gel or other thickeners for a beef stew you are preparing to can, we would recommend not using any. Clear gel would be acceptable from the standpoint of heat stability and providing thickening to the stew, but there is not a TESTED SAFE recipe for doing so. With the addition of a thickening agent, the processing time/weight would change to insure adequate penetration for a shelf-safe product. It would be best to add your thickener of choice when you reheat the soup for eating.

  8. I’m making homemade salsa and it’s to watery. Can I add a flour and water mixture to it for thickening and then can it?

  9. Mary Ann, you can thicken your salsa by adding tomato paste or by draining off some of the liquid. Never add flour or cornstarch to salsa before canning because an unsafe product may result; besides the question of food safety, flour and cornstarch are not stable in high heat conditions and will tend to clump and/or breakdown making the salsa cloudy. The watery salsa can be canned as is and thicken after opening.

  10. My recipe for tomato soup calls for flour and butter to be added after the vegetables cook and you put them through the sieve. Everyone is raving about this recipe but now I am wondering if I should add the flour and butter or wait until I serve it this winter and then add it to the juice I have canned????

  11. Cynthia, so glad you thought to contact AnswerLine. You should not add the flour and butter to your vegetable mixture. Flour does not allow for even penetration of heat throughout the jar so the USDA no longer recommends thicken prior to processing. Rather, figure out the proportion of butter/flour per jar; make a roux of that amount and add to the soup when it is reheated for serving. Not sure what proportions of vegetables to tomatoes are used in the recipe you have; most of these soups contain low acid vegetables so getting the proportion right is crucial to processing a safe soup. Good and quick thinking!!

  12. The question was asked about clear jel and corn starch substitution, but I’m still not quite sure. I did go to the OSU site and plan on using a few recipes, but I wanted to also take a recipe in a canning book I have.

    If my pie filling recipe adds in cornstarch when it’s ready to be baked but not before processing, then can I substitute clear gel before processing and have it turn out safe and appropriate texture and thickness?

  13. Amber, Clear jel must be used if you intend to thicken your fruit prior to processing. If you want to thicken your fruit later, then cornstarch, Clear Jel, tapioca, or flour can be used. Clear jel is the only safe thickening agent to be used with canned fruit. If you thicken with Clear Jel as part of your canning process and it isn’t as thick as you’d like it to be when you use it, you can add a little more Clear Jel (mixed with a little water) or tapioca to strengthen the fruit filling at that time.

  14. If I can’t find any Clear Jel, can I just leave out any thickener and can it without? Then add the thickener later when I go to make the pie?

  15. Jennifer, yes, that is the recommendation we would make. It works very well; just adds an extra step in preparation.

  16. I have just canned a bunch of pear butter. I used the crock pot method. I cooked the pears for 10 hours and then took the lid off and cooked for 4 more. I thickened with cornstarch. I then water bathed it for 10 minutes. The jars sealed with no problem. Do you think they will be safe to eat? I have just seen not to can with corn starch.

  17. Suzanne, I’m sorry to say that you pear butter is probably not unquestionably safe. And as you suspect, it is the cornstarch that is the problem. Cornstarch and flour tend to clump in processing; even that doesn’t happen, there is still a problem because neither of these two thickening agents allow for even penetration of the heat throughout the product to make it unquestionably safe allowing for the possibility of bacterial growth. Instead the recommendation is to thicken fruit with Clear Jel. (I’ll attach a blog piece explaining Clear Jel.) Our recommendation would be store in the refrigerator rather than the shelf and use it as quickly as possible or freeze. https://blogs.extension.iastate.edu/answerline/2020/08/25/clear-jel-vs-sure-jel/

  18. I want to make old fashioned Harvard Beets but I am having a hard time finding a reluable recipe that I can can! Any ideas? Many Thanks!

  19. Peg, there is not a tested recipe for canning harvard beets. However, you could can pickled beets and thicken the pickling juice when time to serve. The pickled beets recipe from the National Center for Home Food Preservation works quite well with the elimination of the onions for turning into harvard beets.

  20. Betty, Allrecipes is not an USDA recommended website for canning information. Cornstarch should not be used in canned apple pie filling. Since you have connected via the blog, Thickeners for Home Canning, you already no why and that Clear Jel is the only thickener that is safely used in pie fillings that are to be canned. The USDA, the National Center for Home Food Preservation, and land-grant universities are the only researched-based, tested recipe sites one should use for canning.

  21. Hello. I decided to can my apple pie filling without any thickener and add it before baking pies. Is there a link to how to do this? Is cornstarch the easiest add in or would something else work best? Thanks in advance.

  22. Hosanna, thank you for your inquiry. Add 3 tablespoons of cornstarch or flour to 1 jar of pie filling right before you assemble the pie for baking. I have found that it works best to remove some of the juice from the filling, stir the cornstarch or flour into the juice until smooth, and then add back to the pie filling. Either cornstarch or flour can be used but it seems that flour is a better choice for apple pie.

  23. If the issue with using thickening products is that it slows the penetration of heat so that it is not evenly distributed, would it not be ok to process the food longer? I have known not to use it, but it has always blown my mind how the heat can penetrate raw meat and not flour! LOL

  24. Linda, there are no tested and USDA approved recipes for using any thickener other than Clear Jel with home canning; infact, Clear Jel is an industry standard. Considerable laboratory time and effort is put into testing products to assure both quality and safety. We need to trust the science.

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