Too much boil off

So this was my 2nd all grain batch and I'm still trying to figure out my system (bought used off craigslist.) It was a Porter recipe a buddy of mine came up with one night while drinking. Everything went pretty well and we had about 5.75 gallons in the boil kettle and started the boil.....

30 minutes in, we ran out of propane... It was a full tank for the 1st batch, how many batches should I get from 17 # tank?

I'm in Michigan so it was pretty cold. After we cooled and filled the carboy, we only had about 3.75 gallons... The OG was about 1.070 but because it was a made up on the fly recipe, we didn't have a projected OG, and he didn't remember the grain bill so we could try to calculate it. We pitched a vial of White labs yeast, no starter. I know Jamil Z says you need to pitch a lot more than that, but I've never had a problem with my extract batches, but never made anything this high of OG before either. I thought about boiling, cooling, and adding some water. How would this change the taste? Is it too late to do that now? This morning there was no airlock activity... I know not to panic yet, but would pitching another vial at this point be beneficial? What do you think my FG will be around?

Thanks in advance for help for a noob.

1. i try for about 6.5 to 7 gallons preboil depending on the amout of hops i am using (more hops= more wort)

2. your propane tank ran out way to fast

3. if fermentation has not started you can add some preboiled water as long as you dont mind your og dropping. you can add more yeast if you want but i wouldnt worry about it to much. in the future if you dont have time for a starter you should use properly rehydrated dry yeast

I'd guess that your propane tank or regulator froze, rather than ran out.

I have done four full boils, one for 90 minutes on a regular Grill tank that wasn't full and I still have fuel left.
If you boiled off 2 gallons in a half an hour I would second the frozen regulator theory. That is a much more vigorous boil than you need.
Your FG will be your OG X the attenuation of the yeast.

I'm pretty sure I ran out... The tank was pretty light... The tank also heats the HLT with my system... My mash tun is a gatorade cooler and the wort is recirculated through a coil in the HLT. A temp controller controls the HLT temp... so it kicks on and off during the mash... I even poured hot water from the HLT onto the tank periodically to keep it from freezing.

Yes, next time I will got with about 7.5 gallons in the boil... hopefully I'll get my stir plate soon and won't have to worry about the yeast anymore!

I get 3 batches with a 60 minute boil out of a 20lb tank. I use a megapot for my boil kettle and need 7.5 gallons preboil to get 5 gallons of beer. thats 2.5gallon boil off which is on the high side.

The gas useage thing will vary. There is a dude here that just the other day measured that he used almost 9 pounds of propane for ONE batch. Well, seeing as though a 20# tank only hols 4.2 lbs of propane... you have a MAX of 18 pounds in there. That is 2 batches and the tank is dry...

You need to really weigh the tank before and after a single use to see what you are using.

Typically from what I have seen, the larger the burner, the more gas (BTUs) are wasted. Keep in mind that these gas burners are only about 25% efficient. So a 100,000 BTU burner at FULL power is only equal to about 25,000 BTUS, or about 7,300W of electrical energy.

Difference being that 7300W of electricity will cost you $.84 over an hour, where as 100,000 BTUs, / 22,000 BTUs per pound of propane equals 4.5 pound of propane, or 1/4 tank, or $4-$5.

You need to weigh your tank before the next brew session, then weigh it afterward... you may want to build some sort of shroud to reflect the heat back toward the kettle, instead of out in to the air.

I will contradict a post above and say yes... your tank is empty. It is TOTALLY possible to run a tank out in less than (2) sessions... totally, but that IS a problem.

I use a 65k btu turkey fryer and do 10G batches. I get 2 batches out of a tank. I know I get good fills from costco. I have the empty tank weight and full tank weight written on it in marker, I find that really helps me get better fills when I don't feel like driving to costco.

Also, run your burner as low as possible to maintain your boil.
This will reduce wasted gas, and has the added benefit of reducing the likelyhood of freezing the regulator.
My roommates and I share a bottle between my 65k BTU burner and a 2 burner BBQ grill. Whoever empties it refills it. Now that I have a keggle, we were able to get 1 batch and about 3 dinners out of a tank.
Next time I'll heat my mash water and sparge water together to see if that makes a difference.

One this which made a tremendous difference for me was to buy a roll of 20" x 10' aluminium flashing at a hardware store. I then cut it in half to get a 5' length, and wrapped this around my brewpot and burner, holding it together with a c-clamp. I used most of a tank of propane on a single brew on Jan 2nd. I bought the flashing and used it as a heat shield, did two batches and when I went to top off the tank, it was only 1/2 empty. Big difference for me!

I only use propane for boils. Strike water, sparge water, etc., can all be heated on the stove for far less energy cost.

I get about 3.5-4.0 batches out of each tank with 60-90 minute boils. In the dry air of winter up here in Wisconsin, boil off is a much bigger factor than the humid summer.