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

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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47 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. . 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.

  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.

  25. I wanted to can an old family relish recipe that uses flour. I have found some cooking (not instant) ClearGel. I also found a 2012 BerNARdin recipe that is similar, except the family recipe uses golden yellow sugar in it, and the newer recipe uses cooking Clearjel, instead of flour. Do I use the same amount of Clearjel as the flour, adjusted by the amount of jars of the end product? Thank you so much.

  26. Hi Linda, Because ClearJel is derived from cornstarch which is a pure starch, it is activated with a shorter cooking time and higher heat without need to remove any flavor; further geling doesn’t take place until it cools. Flour needs to be cooked or browned to remove the floury taste. ClearJel or cornstarch should not be cooked into a roux or browned.

  27. I accidentally used instant clearjel when canning peach pie filling. I know it isn’t recommended because of undesirable results, but is it safe?

  28. Michelle, to be completely honest, I do not know if it is shelf safe as what is important is having the fruit processed long enough to raise the temperature inside the jar to a safe level; with a change in products, I cannot tell you that it is unquestionably safe. To be safe, I would suggest that you freeze the filling if possible as that will be safe. You will have to rethicken when used as the instant clear jel breaks down when heated for long periods of time.

  29. I can a tomato soup and have for many years. It calls for butter and flour. In doing research I now see that neither are ok, so I ordered Clear Jel and will be substituting that and leaving out the butter. I pressure can this for 85 minutes for quarts. Can I substitute the clear jel for the same amount of flour.

  30. Hi Lisa, The only information on Clear Jel is 1/4 cup of Clear Jel for every 1 quart of liquid. Mix the Clear Jel in cold water, then add gradually to the hot liquid, mixing constantly. I have no idea what amount your recipe calls for OR whether your processing time is correct as there is NOT A TESTED RECIPE for tomato soup. You are correct to not use butter and flour. What we recommend for an unquestionably safe tomato soup is to can the Tomato and Vegetable Juice Blend on the National Center for Home Food Preservation website using processing times as given. At the time of use, make a roux of 1/2 tablespoon of butter and 1 tablespoons of flour to a pint; stir in the juice and heat.

  31. What’s the shelf life of Clear Jel? Is it safe to use several years in a row? A local store sells it, but they repackage it so there’s no expiration date listed.

  32. Hi Kimberly, it is best if you check with the supplier of your Clear Jel to determine if it has an expiration date. There appears to be no conclusive answer. One company says it is good for AT LEAST one year or more under proper storage conditions; another company says their product is good 20+ years if stored properly. The proper storage condition is
    a cool, dark place (optimum condition is 60 degrees or less- for longer storage).

  33. I am having a difficult time finding clear gel in my area, and am resorting to buying it on line. I would however like to know if any research is in process or has been done on the safety in practice of pressure canning using tapioca or arrowroot starch as a thickener.

  34. Hi Rachel, while Clear Jel is not readily available like other canning supplies sold in our local stores, it is the only approved thickening agent for canning. Other thickeners are not suitable because they tend to clump during canning and cloud on the shelf rendering the product unappetizing and unable to thicken when baked or reheated. Clear Jel also increases the safety of the products. Because Clear Jel remains clear and does not clump, heat is better able to penetrate the contents of the jar evenly to kill bacteria and other contaminants during the boiling water canning process. Commonly used in making pie fillings, jars of pie filling will keep the same consistency after processing, remain shelf stable for at least 12 months, and bake into a perfect pie by simply pouring the filling into a crust and topping as desired. There will be no starch or flour taste in the filling.

  35. Hi there!
    I was going to pressure can some ground chicken with the packet of “Taco Seasoning” It says it has Potato Starch in it. I’m assuming that is used as a thickener. Is this safe to use in pressure canning. All other ingredients are organic spices.

  36. Hi Eve, thank you for contacting Answerline. To begin, there are no tested recipes from reputable sources for the home canning of ground poultry (be it chicken, or turkey, or other.) Please read and follow the recipe from the National Center for Home Food Preservation: to insure that your chicken will be safe.
    Now regarding the taco seasoning: Even though the amount of potato starch is small in the taco seasoning packet, it should not be used in pressure canning. Following a tested recipe to the T is imperative when canning low-acid foods such as chicken; anything that would interfere with heat penetration may render the product unsafe. Further, potato starch is not stable and will break down during the processing time. However, there are alternatives. You could make your own DIY taco seasoning (some combination of chili powder, ground cumin, dried oregano, sea salt, black pepper, ground paprika, garlic powder, onion powder, crushed red pepper flakes or whatever you like) and add that to your chicken. Different commercial brands package their taco seasonings in different amounts, but most packets contain about 1 ounce or 3 tablespoons of seasoning. A second alternative, and the best, is to can the chicken per the NCHFP recipe above and add the packet of taco seasoning at the time of use.

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