leaving sap in evaporator question

[Mister maple]

Hello . I am new to this and have been getting a lot of my questions answered from all of you with much more experience. I did do some boiling on a homemade , flat bottom pan a couple years ago and was hooked. Then , I did the the days boil and dumped my pan at the end of the day and finished on the kitchen stove. This year I have purchased a Thor Hobby evaporator. It had an 18"x24" dropped flue pan and an 18"x 12" flat syrup pan. My question is this. I am a part time, weekend boiler. What do I do at the end of the day with what is in the pans. I assume I could block off the front pan and finish it and draw off , but what about the dropped flue pan. Can I leave the sap in there overnight, or even for a couple days? Will it freeze and ruin my pan? I should also mention this year I will e set up outside . I thought I would just put my covers on the pan and come back the next day or two and start up but then I thought maybe the sap would freeze???? The sap in the divided dropped flue pan would be partially boiled but when it mixes as it cools it will still be a long way from syrup. Do I need to dump this out and put it back in the next day ?? How cold is safe to leave it? How many days could it stay there ?

[maple flats]

That's a common question for newbees. As long as you boiled hard at least 3 hrs the sugar % is high enough to just leave it in the pan. Even if it starts to freeze it will only form a slush on the top. If more than 2 days before your next boil, light a fire and bring it to a boil for at least 10 minutes, add sap if needed (but only enough to maintain depth, don't add too much and dilute it) and then you are good for 2 more days. Repeat if necessary.
You are actually in more danger if the contents get too warm, that helps micro-organisims grow and feed on the sugar, remedy, boil again at least 10 minutes hard.
Once my season starts the pans are never emptied until last boil of the season, with 1 exception. I drain them to run my flue pan washer, and I also drain the syrup (flat) pan to clean if needed. I determine that by pulling a nylon spatula with the blade faring down about 45 degrees, if it slides easily, no cleaning needed, if I feel drag it needs to be cleaned. If that's the case I drain the syrup pan into my draw off tank. Then I use white vinegar (1 gal in my 3'x3' syrup pan) no added water. I warm the bottom using a weed burner torch up to about 90-110F and let it set. An hour later I check the pan, I use a plastic putty knife to loosen the scale, then when all scale is loose, I drain the vinegar, rinse real well with potable water, then I pump the contents of my draw off tank back into the syrup pan. Any time I'm not boiling I have covers over every thing, the syrup pan, the flue pan has a full cover hood, and all 3 float/draw off boxes.

[Mister maple]

thanks . So near the end of my day i should run my flue pan a bit deeper and give it a good hard boil for a few hours and stop adding more sap. Once I get back to a normal sap level, I can shut it down then and leave it till the next day. I have pan covers so I can cover them and leave them, That helps a lot. I am thinking maybe boil Sat and then Sunday . If I get a surplus of sap or a good early week run, I could also boil Wednesday night for a few hours.

[BCPP]

We run our evaporator on normal years to support our maple festival which is on March weekends (not this year!). As a result we're usually always doing short runs mid week only if required so that we can ensure running on weekend. We've often left for two or three days with no issues. As Dave said, sugar content keeps evap pan from freezing very hard if at all. Two issues we have had: Intake float box freezes fairly solid - does not damage the float box but makes it hairy on startup as the evaporator is starved until it eventually thaws! The finishing pan is also not an issue. On next start up we just bring the firebox back up and we start producing syrup an hour or two after fire up. We have had ,on several occasions, a small bit of scale cause the finishing pan float valve to get stuck open and thus flood which is pain in the neck. We sometimes close the valve between the two pans but need to be sure latent heat in the firebox cant boil the finishing pan dry.
Our bigger issue is shutting down in warmer weather where microbial growth can spoil the sap in the evaporating pan.