Rainbow film on boiling sap

[rbeaton]

First timer here, using a 2 burner propane stove with new stainless 6" steam trays.

It's been going for about 2 hours, and we've noticed a sort of rainbow looking film on the surface of the boiling sap. There is definitely some rainbow discoloration on the pan itself, presumably from getting it too hot, but this is on the surface of the sap. The pans were washed before use, but this is the first time heating them. Sap was collected in 5 gal blue buckets from Bascoms (the closed ones with the 3" or so cap on them). I did not wash the buckets before hooking them up to collect the sap.

I've dumped off the boiled sap into a another pot, rewashed the pan, and am trying it again with new sap.

Is this expected? Or some sort of residue from the pans?

Thanks!

[Maple Man 85]

A rainbow film would indicate some sort of oil based residue. Did the sap have the film before it was boiled? We collect by bucket as well and if we have sap that is discolored I dump it.

[Sinzibuckwud]

could be some residual soap in the pan or unwashed buckets.

[rbeaton]

There's nothing visible on the sap before boiling. I have a second batch going now and I haven't seen anything yet, so I'm thinking that it's probably from the pans, either some sort of residue from manufacturing, or like Sinzibuckwud said, from when I first cleaned it.

Thanks!

[happy thoughts]

Could it be coming from your propane? Propane can leave an oily residue.

[DrTimPerkins]

could be some residual soap in the pan or unwashed buckets.

I think this is the most likely diagnosis. Soap ALWAYS leaves residue. You should try NOT to use soap when cleaning maple equipment....just lots of clean hot water. If you do use soap, then double-rinse, the double-rinse again.

The second most likely cause would be oils left over from the pot manufacture.

[rbeaton]

I think this is the most likely diagnosis. Soap ALWAYS leaves residue. You should try NOT to use soap when cleaning maple equipment....just lots of clean hot water. If you do use soap, then double-rinse, the double-rinse again.

The second most likely cause would be oils left over from the pot manufacture.

Thanks for the reply Tim. I had read that you shouldn't use soap, but I guess I wasn't thinking that would apply to a portable stainless steel pan.

The second batch had some of the same look, but not as significant as the first. Enough though for me to dump the sap - regardless of what it was, I don't think it's anything that I want in my syrup!

I cleaned the pans out as best I could tonight with just hot water and rinsed fully multiple times. I still have some fresh sap left from today and will try it out again one night this week.

I did take a few cups of sap and throw them on a regular sauce pan on the stove, and those boiled down with no sign of what I was seeing in the larger pans, so fortunately it doesn't seem to have anything to do with the buckets.

I'll try again as soon as I'm able and we'll see what happens!

[rbeaton]

Just wanted to provide an update and thank everyone again for the suggestions.

I thoroughly cleaned the pans with just water and ended up switching to a stove that was burning much more cleanly (the first one would not get a good blue flame, and I ended up getting a refund for it). Whether it was soap, manufacturing residue, or a dirty flame, the problem was resolved and I got my first 3 qts this weekend!