Marrow Jam

This is part 3(4?) in my continuing quest to use more zucchini. Richard suggested this one to me. Apparently the brits call zucchini 'marrow' which is why my google searches for zucchini failed to yeild this excellent recipie

1 kg peeled and seeded zucchini
1 kg sugar
2 lemons
1 Tbs fresh ginger, finely chopped

1.Cut the zucchini into chunks and combine with the sugar in a saucepan.
2.Add the zest and juice of 2 lemons and the minced ginger.
3.Slowly bring to a boil and then boil over moderate heat until it reaches jelly stage.
pour into jars and cool.
Refridgerate until you're ready to eat it on toast.

IMPORTANT. I DO NOT KNOW IF THIS IS ACIDIC ENOUGH TO CAN. DO NOT CAN THIS, ESPECIALLY AT ALTITUDE UNLESS YOU HAVE A pH METER. My friendly local USU extension rep says the following when I emailed about this recipe : "I also can't tell if it is acidic enough to can. Usually canning recipes use bottled lemon juice, because that is the only way to tell if it has 5% acidity. Zucchini is very low acid and cannot be canned by itself."