Today’s post is inspired by a rash of questions I’ve gotten recently in regard to my recipe for Honey-Sweetened Peach Vanilla Jam. A number of you are concerned because while that recipe contents lemon zest, it doesn’t contain any lemon juice. That jam is safe as written, but we need to dig a little deeper into canning science to understand why. Read on!
If you’ve been canning for any length of time, you’ve probably heard mention of acid levels in relation to safe boiling water bath canning. Anything that is preserved in a boiling water bath must have a high acid content. The reason that high acid levels are important is that the presence of acid inhibits the germination of botulism spores into the botulism toxin. Botulism spores can only develop into the botulism toxin in low acid, oxygen-free environments.
When you preserve something in a boiling water bath canner, you heat the jars and their contents to the boiling point (that temperature varies depending on your elevation, but at sea level the boiling point is 212 degrees F). That heat is enough to kill off the micro-organisms that can cause spoilage, mold, or fermentation, but it’s not enough to kill botulism spores (they require far higher temperatures). The process of boiling the jars also helps to drive the oxygen out of the jars, creating a vacuum seal. For jars that have sufficient acid content, the result is a jar of food that is safely preserved and shelf stable.
The way food scientists (and home canners) determine whether something is high or low in acid is by pH. If something has a pH of 4.6 or below, it is deemed high in acid and is safe for boiling water bath canning. If the pH is 4.7 or above, it is considered low in acid. We’ll talk more about how to preserve those foods that are low in acid and have a pH of 4.7 or above another day, but to give you just a hint, that’s often where a pressure canner comes in.
If a food is close to the 4.6 pH point, you can often add enough acid to bring that product into the necessary safe zone. Fruits like tomatoes, figs, asian pears, melons, persimmons, papaya, white peaches and white nectarines, and bananas are often just a bit too low in acid in their natural state for safe canning. So in order to lower the pH to a safe level, we add either bottled lemon or lime juice, or powdered citric acid to products featuring those ingredients. Once the acid levels are high enough to inhibit the botulism spore’s ability to germinate into a deadly toxin, that product is safe for boiling water bath canning.
However, there are a world of foods out that naturally have a pH that is well within the zone for safe preservation in a boiling water bath canner. Here’s where we come around to the peach jam I mentioned in the introduction to this post. That recipe specifically calls for yellow peaches, which typically have a pH of 3.4 to 3.6. Charts like this one allow you to check on the general pH chart for various fruits and vegetables.
You could certainly add lemon juice to my jam in order to balance the flavor and add a little extra pectin (citrus fruit is naturally high in pectin), but it’s not necessary for safety.
Updated to add: One last thing! It’s important to remember the pH of the entire jar counts here. This is why it’s so vital to follow tested, reliable recipes for things like tomato sauce or salsa. Sure, you can add bottled lemon juice to your tomatoes to lower the pH, but if you’ve also added onions, garlic, and basil to your sauce, you’re not just balancing the acid of the tomatoes, you’re also taking the rest of the ingredients into account. That’s why salsa recipes designed for canning contain so much bottled lemon or lime juice, or vinegar.
I canned white peaches using your peach jam recipe in Food In Jars cookbook, and it called for fresh squeezed lemon juice, not bottled lemon. I did not use pectin but it set beautifully. However! I this article you mention whote peaches are low in acid snd that bottke lemon juice is what shoukd have been used. Can you tell me if your peach jam recipe in your book was safe for white peaches?
White peaches do have a lower acidity than yellow peaches. However, the chance of that jam creating an environment for botulism germination is very low.
I have a very good question to ask about ph in food ,if i want to water bath can something ,and it isnt a high acidic food -can i just add lemon juice or vinegar to the jars to acidify the ph UP ??? like eggplant -its low in acid ,couldnt i take the eggplant and add lemon juice and vinegar to raise the ph of the liquid in that jar -and would it be safe? the recipe im referring to is from “baba ganoush recipe -and its thick and rich
the same question for syrups -i have a packet of kool aid powder mix ,i want to make a heavy simple syrup out of it -i take 3 cups of sugar and 1 cup of water and the packet of kool aid make the syrup without any hard crystals forming -it looks right -taste sweet and the flavor is there – NOW i add lemon juice -like a splash or 2 to the liquid -it reads 4.5 ph – did i do it right ? is this SAFE .for me to can ?
i mean dont we just add acid to our product to can ? or is it STILL unsafe for us to can this way ? nest to can in a pressure canner ?
please feel free to write back if you have any answers -and thank you in advanced -im sure these questions are not easy ,but still need to be asked.
When canning adding lemon to each jar it will not matter what you added it is so much per wt or pint.ò
It really depends on the recipe. When you are doing something like tomatoes, you should add 1 tablespoon bottled lemon juice to every pint of product and 2 tablespoons to every quart, to ensure you have the proper amount of acid per jar.
How do I measure the PH level in my tomato juice _ sauce? Please Help!
I want to add onion garlic basil and peppers or should I just addd after you do the water bath process? Can I just use my Large soup pans for water bath or is that unsafe? I am disabled and can’t afford 250$ to buy one? Any ideas where to buy one cheaper if I can’t use my Large pans?
Kindest Regards, Monica Parker
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330-807-0827
You need to be following tested recipes. If you’re not able to do that, you are better off freezing your sauce. If you are going to proceed with canning, leave the garlic/onions/peppers/basil out and just can the plain sauce. A big stock pot or soup pot can be used as a canner but it needs to be big enough for the jars to be fully submerged in the water. A basic enameled canning pot shouldn’t run you more than $30 if you do need to buy one. You could also ask around and see if you have any neighbors with a pot that you could borrow.
Horseradish Greens – can one simply add vinegar to the greens when cooking them prior to canning, hence, eliminating the pressure cooker (mine is quite small)?
Charts say that greens are 5.3+
If so, how much?
There no formula where you can take the thing you want to can, plug in it, and have it spit out how much acid you’d need to add. To process horseradish greens in a boiling water bath canner, they’d need to be actively pickled, but I don’t know of any recipes out there for pickled greens. You can take a look at the National Center for Home Food Preservation website’s pickling page to see if they have any more information, but I suspect this one will be a no go. https://nchfp.uga.edu/how/pickle
Am I thinking correctly that if you make a product that’s usually under 4.6, and use litmus paper to test the Ph it is above 4.6 — you can pressure can the product for the same amount of time it would’ve taken in a water bath? Thank you.
Not everything can be pressure canned. Some things, like low acid purees, have a density that prevents the heat from fully penetrating the product, which can lead to an unsafe finished product. It’s really best to consult a reference like the National Center for Home Food Preservation before canning something.
Have a question if when you open a jar of home canned tomatoes canned in their own juice if you test the ph and it is 4.5 or lower does that mean that the jar is safe from botulism growth?
Yes.
Greetings! I am interested in making a mulberry jam that can be stored long term. I do not want to add any sugar and was thinking of using a little cornstarch as a thickener. I make pancake syrup this way with the mulberries and it preserves the natural taste of the berries the best way. But with the cornstarch, can I still water bath or should I use a pressure canner? I am concerned the corn starch may change the way the temperature of the water penetrates the jars. Could I just boil them longer? say 10 or 15 minutes? I found plenty of recipes using corn starch to thicken, but only for use within a few weeks and not canning for long term storage. Can find no information other than that the corn starch will change things, but no information on what to actually DO to keep it safe. Any help or suggestions?
I don’t recommend doing what you’ve suggested. Cornstarch is not a shelf stable thickener and so the mulberries might end up runny again over time. It also causes density issues, like you suggested. If you want a sugar-free mulberry preserve, I recommend you cook and can the berries without any thickener and then thicken with a little cornstarch once you open the jars.
Will adding jalapeño or habanero powder cause an issue in my strawberry jam
It should be fine in small amounts.