Way too much boil off

How much hops did you use? And leaf or pellet?

 

I was dealing with very similar issues, all grain, new mash tun kettle and burner. I only lost a quarter of a gallon, if you really wanted to, you could add water to make up the missing volume. I would boil it (the additional water), Oxygenate it and add during fermentation. It will naturally mix with wort and you should be at your good happy place.

 

Have you tried changing your equipment profile in your brewing software? Dialing in new equipment is sometimes trial and error.

 

I came across this some time ago:

You boil off rate is dependent on kettle geometry, intensity of the boil, and to a smaller extent, the humidity. If you are experiencing the 70-80% humidity we have been having here in Nebraska the past couple of weeks, the humidity may be playing a little bigger factor.

One of the fixed factors is kettle geometry. A kettle with a large surface area relative to the depth will have a larger boil off rate than a deep narrow kettle. If you switch to a different shape/size of kettle, your rate will change.

Intensity of the boil is a factor a lot of folks have problems with. You need a good rolling boil, but not so violent it splashes. A slow simmer will not give you the mechanical agitation you need nor the evaporation you want.

There is really no real formula for computing length of boil relative to the humidity. One thing to keep in mind that for a given kettle and a consistent intensity of boil, you will boil off very close to the same volume per hour every time regardless of the actual volume of wort you start with. In other words, if your boil off rate is one gallon per hour for your kettle (a pretty normal rate for a lot of folks) you will boil off that same amount whether you start with 5 gallons or 25 gallons in that kettle.

Some folks like to compute their rate as a % per hour. Not a good idea. That works only if you have exactly the same volume in the kettle every time to start. Boiling off 1 gallon from an initial 5 gallon batch is a 20% boil off rate. If you boil off 1 gallon from an initial 10 gallon batch, the percentage is only 10%. Smaller differences will of course give you smaller percentage differences, but a half gallon difference in starting volume will throw your percentage calculations off.

https://www.homebrewersassociation.org/forum/index.php?topic=3187.0

 

When I upgraded to a larger diameter kettle, my boil-off rate greatly increased, too. I had to adjust my mash/sparge water by adding a gallon to everything calling for a 90 minute boil.

 

The recipe may have had an OG of 1.050, but your OG increased proportionally to the reduction in volume due to boiloff.

 

how were you 1.75 gallons short and only 6 points over?

based on those numbers, had you had 5.5 gallons, your beer would be 1.035, 10 points short.

something is amiss, you measured something wrong at some point or didn't have good conversion during your mash.

 

what was your sg and pre boil volume?

 

Since the only thing that boiled off was water, adding it back post-boil will simply bring your gravity back down to where it would have been without the excess boil off.

 

Put some water in your new kettle. Do it with 1 gallon at a time. Fill up a milk jug, and pour it in. Get a CPVC stick, cut it to length.

Put it in your kettle, mark 1 gallon. Repeat until you are near the top.

Bring it to a boil. Check at 30 minutes, mark the level. Check at 60 min and mark the level. From there, you can figure out roughly what you boil every 30 min to an hour, and can move it around based on the losses for your boil length. Use the hot water to clean something while you are at it.

There on out, you can check your volume easy enough.

 

How was your final gravity? seems like if you everything the same but boiled off a whole bunch more, it should have been off by quite a bit (on the high side).

And a 15 gallon pot for 5 gallon batch will significantly change your kettle geometry over what many of us use (for instance, I use turkey fryer pots, like many others). As others have stated, you'll have to adjust to this by "dialing in" your new system.

 

Or try this cool way to permanently mark the inside of your kettle, provided you don't mind removing a small amount of metal

"How to add permanent volume markings to a kettle.
This method uses electrolytic acid etching but requires nothing but cheap household materials! The hardest part is taping off where you want the marks to be. This works by actually removing metal only where the current flows."

http://imgur.com/a/dCvS5

 

That's cool.

 

Seconded on awesomeness. My kettle already has stamped volume markings but this looks so cool I want to do this too.

 

I will echo what's been said, that math doesn't add up at all. Somethiings off on either your gravity readings or your actual volume.