Minimum boil off

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SkiNuke

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I currently boil in 2 pots because I am cheap and didn't want to buy a large pot and a gas stove. However, about 6 months ago I splurged and got what I needed to get off of the electric gas stove. Unfortunately, I didn't ask my apartment management until after I got the stuff whether or not they allowed gas stoves on the porch and they told me it's against code. As such, I kept with the same 2 pot boil method.

Last night, I did a boil test with my large pot and plain water and discovered 2 things. First, my tap water is almost hot enough that I could mash with it (144F) :D. And second, I actually can get it to a boil on my stove if I put it on two burners. It took almost 45 minutes to get it to a boil (I lost about a half liter during this stage), but once there I boiled off about a gallon of water in 60 minutes. Now, the boil wasn't as strong as it has been in the 2 pot system where the boils have been frothing and insane, but it was moving even though the very center was relatively smooth (kind of looked like an small eddy).

Now for my questions:
1) How much boil off is considered the minimum to avoid things like DMS? Would a half gallon be enough, or is 2 gallons more in line with what's needed?
2) Does the boil above sound like it will be good, or should I just stick with my current 2 pot system?
3) Is this a good test of what will happen when I actually brew? I would assume the added sugar won't affect the ability or rigor of the boil much if at all.
4) Any other thoughts?
 
You want a nice, steady boil. It doesn't have to jump out of the pot, just nice and steady. I boil off about 1.5 gallons per hour and have no DMS issues. You can try it at 0.5, but that seems pretty low. It might work for standard 2-row, but you might have to boil longer for pilsner recipes.
 
I don't think vigor of boil has that much effect on DMS. As long as it's boiling and you keep the lid off, you should be good to go. It will alter your hop utilization slightly which will change your bitterness slightly. More vigor = more utilization = more bitter. I would use the large pot and do full boils personally, a reduced boil off will not harm the beer. And lastly, yes, that test run should be indicative of what to expect on brewday. If you're worried about it, you can boil up a small amount of water, say 1 gallon or so with one of your other pots and have it cooled and ready in case you boil off too much and need to top off. After the first couple batches, you should know exactly what to expect and can ditch boiling the extra water.
 
Thanks. That was exactly what I wanted to hear. I might do a 90 minute boil regardless so I can sparge with a bit more water.
 
I too have a boil question. Will the increased density of wort vs. plain water increase the temperature at which it boils?
 
I too have a boil question. Will the increased density of wort vs. plain water increase the temperature at which it boils?

No. Water is the deciding factor. Once it reaches boiling point, steam will evaporate shedding heat. The only way to increase temperature significantly would be to boil under pressure, like in a pressure cooker.
 
No. Water is the deciding factor. Once it reaches boiling point, steam will evaporate shedding heat. The only way to increase temperature significantly would be to boil under pressure, like in a pressure cooker.

While water is the main deciding factor, that's not the only deciding factor. Solutions' boiling points are dependent on their densities. However, the change in density probably would not be significant enough to do anything (so you are right there), but there would be a difference.

http://chestofbooks.com/food/science/Experimental-Cookery/The-Boiling-Point-Of-Water-And-Solutions.html#.USqzNRIS3SY
 
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