Trouble hitting fermenter volume

[ChicoBrewer]

I have been chasing my tail on this. It seems I'm constantly boiling longer or topping off to hit my fermenter volume. The other day I did an experiment to try to determine my boil evaporation rate. I boiled 7.5 gallons of tap water starting the clock at the time the water reached 112. The result was 6 gallons left in the kettle. Now I realize that isn't the story. I think wort coming out of the mash tun is around 170 (maybe) and it takes some time to reach boil. All the while there is boil off. I adjusted my boil evaporation rate to 1.5 gal/hr but I fear I'll be adding water next time. last time I had to boil longer (90 minutes versus 60)

What are the points I need to measure to get a better number?

Here is the quick water requirements for one of my recipes (A Pale Ale). everything is in quarts.

Strike water volume at mash thickness of 1.5 qt/lb = 18.7
Remaining sparge water volume = 16.2
Grain absorption losses = -6.2
Amount going into kettle = 28.6
Boil off losses = -4
Kettle dead space = -2
Hops absorption losses = -0.6
Amount going into fermenter = 5 22
Total: 34.8

Now thinking through the brew day first I heat ten gallons of water to my strike water temp. Now I mash. This one is a single step so now I drain to the kettle. Meanwhile I have been heating the water that is left to my sparge temp (170). I sparge twice using half of the remaining sparge water volume each time. now I boil. I think it takes about 40 minutes to get the wort to boil.

I consistently over or under shoot.

Is there a way to get this right on my next brew day? where do I measure to dial it in?

~Scott

 

[philjohnwilliams]

If you are breeing outdoors then weather conditions will affect your boil off rate. A change in relative humidity or even a different breeze can make your rate change. I live in Montreal and brew outdoors year round and my boil off rate in the winter (very dry air) is nearly twice what my summer rate is. I added a sight glass to my kettle so I can monitor my kettle volume and adjust my burner to compensate and that has helped my hit my volume targets.

 

[Hawkbox]

It was humid as hell here today and my boil off rate was about 1/2 gallon below what it normally is.

 

[J A]

That^^^
Also if you're using gas, it's a little harder to control boil vigor. I always keep it boiling vigorously because, among other advantages, it seems easier to maintain fairly consistent boil-off from brew to brew as opposed to a lower-energy boil.
Have you been using the same equipment and process for a lot of brews and still can't get a handle? Are you checking pre-boil volume carefully?
Assume a little lower average and you'll end up adding water to top off. That's the easiest. Also, shoot for more than the minimum going into the fermenter. If you're less than a half gallon off at the end, you'll be less than 5 gravity points off on most beers, assuming your mash efficiency percentage is fairly constant. You have the option of adding a little water or a little extract to make your beer what you want it to be. No sin to do either.

 

[ChicoBrewer]

Well I have a certain advantage living in northern California on the edge of the cascades. It doesn't rain at all from May to October and it remains around 100 degrees from June to mid September. I should be able to dial in my summer brewing easily enough. It's 91 right now and 30% humidity. The only thing falling out of the sky are ashes from the fire just outside of town up in Bidwell park.

Right now my plan is to measure volumes carefully at each step with my next batch including just before the boil starts. I'm getting pretty good at this pale ale thing so it doesn't seem like a waste.

Yes I have been using the same equipment but I only have seven all grain batches under my belt. Now that I have my rather odd volume graduations maybe I can measure more carefully.

 

[J A]

I have about 7 batches into a new system but since I'm using the same procedure that I've been used to, I was able to get good estimates about a lot of stuff that I couldn't measure (things like dead space are easy to nail down). I had a couple of brews that were very different from projected efficiency and some volumes off by a little, but for the most part things were plenty close and the beer turned out great. The last brew I did, the numbers were spot on right down the line.
I have the advantage of boiling electric and I think that helps with keeping boil very consistent. And it's been nothing but stupid hot and fairly humid every time I've brewed. Things will likely change in the dead of winter.

 

[GFHomebrew]

Well last brew two days ago i was 2 lt short and 8 points high on a brew. 1 i opted on a no squeeze on Biab Bag and 2 i opened the gas bottle valve right open. i think that the brew before (which i was over in volume) i had a lower burn rate because i didnt alow good gas flow by opening valve right up. Anyhow i diluted as JA said as the boil was in process as i saw with 15 left i was already below 21lt. So yes ive brewed many a batch on my rig and still manage to come up sort now and again.

 

[Nosybear]

Also, don't over think this. In your shoes I'd plan for adding water: Boil to hit a bit less volume than you want, then add boiled, cooled water to hit your target OG. May affect hop utilization a bit but not so much you'd notice.

 

[Hawkbox]

I live in Alberta, where the humidity is usually in the negatives year round. So this week has been weird with storms and water everywhere.