I have 6 different types of grapes on 7 vines grown on a 2-story high trellis; so, I get way more grapes than our 3-person household can consume fresh. The surplus seedless grapes are all converted to grape juice and the juice is pressure canned to store it long term.
Something peculiar is that the juice of the Himrod grapes, the most productive variety, turns pink or red from its initial grey/green color during the canning process. The color seems to depend on the canning temperature; it’s usually pink when canned at 6 psi and dark red when canned at 7.5 psi (something that I discovered by mistake today). Does anyone know what is the chemical reaction that creates this color change? I could find nothing on the Web about this.
I’m also interested in processing the grapes by using a blender to chop the grape skins up and incorporate their nutrients into the juice. That would eliminate the need to run the grapes through a Victorio food strainer. I already force as much of the pulp as possible through the strainer, which takes some extra time and effort. Does anyone here have any experience with blending whole grapes? Is it best done before or after cooking them? Thanks.
Would be interesting to test pH of different colored juices from same batch at different psi.
Not that you want to buy another appliance (!), but using a steam canner is my very quick, alternate method of canning grape juice from both seeded and seedless grapes. If desired, you could add in some of the grape mash from the seedless batch at the end. No food strainer involved unless you wanted to add in a finely blended mash.
The process involves steaming the grapes over boiling water with an in-between spouted catchment pot. When the steamed grapes have reduced by 3/4, I drain the steamed juice into hot quart bottles and cap. They all seal from the hot juice cooling. Very quick!
I usually can about 24 quarts of grape juice plus apple and pear juice from surplus.
i have one as well. do you mash your fruit once they have softened? your juice is pretty clear so im guessing you dont. i like to crush mine a little to help the juice release but then you get more pulp in the juice.
I mash a bit with the grapes. With apples and pears I can the pomace separately as a thick apple/pear sauce. Aside from my dehydrator, I think the steam juicer is my best preserving appliance!
Thanks - will try that with citric acid I have on hand for dipping pears before drying.
i made a bunch of cherry juice with my sour cherries and black currant juice. the chics get the pulp and seeds. black currant juice is so rich i have to cut it by half with water. tastes like a rich concord grape juice.
@lordkiwi, I’m not trying to protect the original color, which is an ugly gray/green. I like the pink or red colors that come with pressure cooking, but I’m curious about why the color changes. Also, grapes already contain a relatively large amount of antioxidants.
@cdamarjian, thanks for your comments about steam canners. I’ve tried steam-cannng by using my pressure canner without applying any pressure. It works fine, but, as mentioned above, I prefer the color of the pressure-canned juice. I also want to incorporate as much of the grape pulp and skin into the juice as possible. Many of the nutrients in grapes are located in the skin.
The pink/red/purple color in grapes is due to a class of chemicals called anthocyanins. These can also exist as a colorless form called leucoanthocyanins. Heating these compounds in an acidic environment like fruit juice can convert them to the colored form.
If you have ever cooked quince and had it turn pink, the same process was at work.
Thanks, GrapeNut. That’s exactly the information that I was looking for.
I have himrod and the vine has been building up, next year I’ll probably have enough to juice. I was planning to pressure can it, it would be nice if it was pink instead of grey!
I’ve noticed with other grape juices that if I don’t get all the skin out, it can make me nauseous to drink it later. I strain really well now, stems and pits I remove then I cook down in water the remaining flesh then strain well to get the skins and most pulp out. then can it.