Can you believe how click-baity that title is? (Is it still click bait if the post actually lives up to the title?) In fact, I plan to deliver on the promise of that title, because if you’ve gone to the trouble of foraging for wild/feral grapes, juicing them, and straining the juice, I don’t want you to make this major grape jelly mistake.
Here’s the science-y part: Grape juice differs from many other fruit juices in that it contains large amounts of both potassium and tartaric acid. At temperatures below 40F, these substances bind together to form crystals of potassium bitartrate, and if those crystals aren’t removed from the juice, you’ll end up with crunchy bits floating in your jelly. It’s perfectly safe to eat (in fact, cream of tartar is finely ground potassium bitartrate), but who wants crunchy jelly? Not me.
Fortunately, this problem is easy to solve; all it takes is time and a fine strainer. The instructions below pertain to all grapes: foraged, garden-grown, store-bought, white, red, and purple!
How to Eliminate the Crunchy Bits
After you’ve strained the fruit and collected the juice, pour the juice into containers, cover them, and refrigerate for 24 – 48 hours. I’ve read suggestions that 12 – 24 hours is enough, but I’ve found many more additional crystals form after the initial 24 hours, so go for the full 48 if you can stand to wait. Then, slowly pour the juice through a jelly bag or cheesecloth, into a new container, being particularly careful as you reach the bottom of the original vessel. Here’s what you’ll find there:
Once you’ve eliminated the tartrate crystals, your juice is ready to turn into jelly, or syrup, or just enjoyed as juice. And you can rest assured no one will find unwelcome crunchy bits in their PB&J sandwich. Disaster averted.
Wow, how interesting! Thanks for sharing the science behind this phenomenon, and for the advice. I have some grapes in the freezer waiting to be turned into jelly – this is a jelly saver!
Glad to help, Carolyn! Let me know how your jelly turns out.
How would I avoid the tartrate crystals in jam. Has a thick pulp. I have had problems with it. Can’t find info on jam and tartrates. I have left sit in fridge to settle to bottom. Use pulp on top .. But still sometimes end up with some jam that has it.
I’ve never heard of this happening with jam, but then again, most people don’t make grape jam because it’s so labor intensive to separate the skins, seeds, and pulp. So I can’t speak from personal experience, but here’s my best guess: after you’ve separated the seeds from the pulp, re-strain to separate the pulp from the juice. Refrigerate both, separately, over night, and the next day strain the crystals from the juice. Recombine the juice and pulp, add the chopped skins, and proceed as usual. I’m really not sure this will work, because some tartrate crystals may be held in the skin and pulp, but it’s the only thing I can think of to try. If you do it, please let me know how it goes.
Thanks for the advice. Im thinking some of the crystals may still remain in pulp too. There has to be some method out there I just cant find it. I have made it before without a problem . But I believe I hav always processed everything and set in fridge for a day or two which apparently causes crystals to sink to bottom. But its hard to make sure you only take from top and dont get to close to bottom. Havent found way to strain pulp to thick. I might try your suggestion . If I find the answer I will let you know.
I personally like those crunchy sweet/sour little crystals in my homemade grape jelly and juice… I’ve been eating them for decades and enjoying them and honestly, when you put the jelly on bread with butter or peanut butter and then eat it, you don’t really notice those crystals most of the time… all a matter of preference and labor, I suppose.
You’re not the only one, Jonas! I have another friend who feels the same way. I say if you’re making the jelly, make it the way you like it. I’m just glad you’re making your own jelly!