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I'm boiling down some maple sap this year on the stove top. A bit late but thought I'd give it a whirl even if it only yields a quart or two of maple syrup.

Will keeping the hood vent on increase the rate of evaporation?

Conventional logic makes me think yes, but I just read a few threads on this topic and left feeling a bit confused since some people indicate that the hood reduces the surface temp and creates an inconsistent boil which can decrease the rate of evaporation.

EDIT: Since there has been some discussion below in regards to the type of hood vent being used so I'll add this: It's a fairly standard residential hood vent that vents to the outside through the ceiling (not the recirculating kind). When it's on it is definitely pulling steam out of the kitchen — I can see the steam flowing up through the vent.

Also, the pot is on at a simmer. The amount of steam being produced here is not a large quantity and the hood seems to do an adequate job of removing all of it. For purposes of answering this question, please assume that the vent is removing steam. The question in this case is, will removing steam at the rate which it is produced increase the rate of evaporation.

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    To get rid of all sticky issues (pun intended), I encourage you to focus primarily on the influence of venting on evaporation rate and leave the question of sugary condensation to a side note at maximum. If it helps, think about boiling down stock for a glace instead of maple syrup. – Stephie Mar 28 at 12:04
  • Thanks @Stephie - yes I am primarily focused on evaporation rate. I've been experimenting with the vent as I go and so far it's hard to tell because the evaporation rate even at a simmer is exceeding the sap output of the single tap I have. That said, it looks like I'll end up with just under 1/2 gallon of syrup over the course of 6 days. – billynoah Mar 28 at 14:45
  • Also, for the record, nothing is soaked, there is no sticky film and the smell is delicious. I only wish I'd done one more tap. Next year :-) – billynoah Mar 28 at 14:46
  • billynoah, if you are not satisfied with the existing answer and have gained some knowledge through your own experience now, it would be perfectly ok to self-answer your question. Just a thought, considering the amount of comments we mods have been deleting so far. – Stephie Mar 28 at 15:59
  • @Stephie - It's ok. I still honestly don't know. I suspect that the vent decreasing humidity would have a net positive effect but as I said I've had to dial back the heat so much that it's become difficult to gauge. I'm ok if this remains without an accepted answer for now until something convincing emerges. In the meantime, the existing answer does provide some useful content for browsers of the internet. – billynoah Mar 28 at 16:15
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I'm boiling down some maple sap this year on the stove top. A bit late but thought I'd give it a whirl even if it only yields a quart or two of maple syrup.

It takes between 20 to 60 quarts of sap to make 1 quart of maple syrup.

Will keeping the hood vent on increase the rate of evaporation?

You'll want to do it outside, too much steam; sap is mostly water. If you are insistent on doing on the stove top then keep the hood fan on, enjoy the smell, and be prepared for flies and bees to have an inexplicable attraction to all the surfaces near your stove.

Your kitchen stove's hood fan is too far away to affect the boiling, or capture all the sticky steam. 20 quarts is 5 gallons, and 60 is 15. A 6 gallon pot is approximately a foot diameter and a foot high. Providing those measurements in metric won't make it seem any easier. :)

Conventional logic makes me think yes, but I just read a few threads on this topic and left feeling a bit confused since some people indicate that the hood reduces the surface temp and creates an inconsistent boil which can decrease the rate of evaporation.

Venting is necessary, even outside it's desirable, just to get rid of the steam. In your case you'll want to vent, and there'll be no effect on the temperature. Professionals vent, those that don't say that the next thing they are doing is inquiring about getting some vents.

Check out these two threads, it's all steam; everything will be soaked.

DIY Maple Syrup

Professional Operation

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    Hi Rob, thanks but I am not seeking advice about maple syrup production here. This is a question about the affect of a range hood vent on evaporation rates. – billynoah Mar 24 at 14:10
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    In addition to answering that question I added additional information for people making the decision to boil their own at home. – Rob Mar 24 at 14:21
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    What is the answer to "Will keeping the hood vent on increase the rate of evaporation?". You mention a smell, a sticky film, that I should do it outside, that I "want to vent", and even somehow you know the distance of my hood vent from my range. I don't see anywhere in your answer where you address evaporation rate. What did I miss? – billynoah Mar 24 at 15:51
  • @Rob - No my hood is not that powerful or close, but also consider I am not producing that much steam. From what I can see, the vent is in fact, removing most or all of the steam that's being produced while it is on. I've added this info to my question. – billynoah Mar 27 at 16:44
  • @Readers please note that these additional points of clarification were addressed a few times here and in comments to the answer. Many replies have been deleted. --- Several people are satisfied and some are not; regardless, the arguing has not been productive and I have something else to do. – Rob Mar 29 at 13:17

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