At what canning temperature does niter form?

[buck3m]

Canned a batch today and am disappointed to see the tell-tale clouds that will settle out as niter.

We use cone filters. The last two seasons we didn't have a bit of niter. We brought the canning temps up a bit this year and I'm wondering if that caused it. I reheated the syrup to 200 degrees then ran it through an Orlon cone filter which seems to be in good shape.

A few hours later after the syrup was all filtered, I put it in a big double-boiler (no flames touching the bottom of the syrup pot, only hot water) to reheat it to 190-195, finally transferring it the canner itself. The canner sits in a shallow pan of water with spacers to keep it off the bottom, so the temps are held at very close to 190 by the hot water, which sometimes reached boiling.

Seems like we did things just about the same last year, except for temps maybe 5 degrees lower

Ideas of where the niter came from?

[ShLUbY]

I've always read that nitre forms at 195 degrees and higher, so if reheated to that or higher after it's been filtered will result in nitre formation. I have already recanned a batch of syrup this year because i forgot about that little detail! HA! Good luck to you! I had to pull taps today :( too warm now! on to Morels

[buck3m]

I've always read that nitre forms at 195 degrees and higher, so if reheated to that or higher after it's been filtered will result in nitre formation...

I've heard that too, but many authorities, like Leader and Cornell, say something like "optimal canning temperatures are between 180 F and 200 F degrees." I kept an eye on temps and I am pretty sure the syrup never reached 200 after filtering. I thought I was safe with the double/boiler type setup to prevent hot spots on the bottom.

[maple flats]

I think niter can form anytime you heat it to higher than the temp it was filtered at. I now heat it to 205-210 and filter it, then I can between 185-195. I don't seem to get niter that way. Another factor might be the time and evaporation that occures at lower temps. I believe, if you heat it to say 185 and lose enough "steam vapor" off the surface, more niter can form.

[buck3m]

I think niter can form anytime you heat it to higher than the temp it was filtered at. I now heat it to 205-210 and filter it, then I can between 185-195. I don't seem to get niter that way...

I think there might be merit in that idea.

Found this interesting article on filtering. http://www.atkinsonmaple.com/files/FilteringSyrup.pdf