Please help me understand water volumes

[Alex4mula]

I have done 4 extract brews and two of those were completed and gone (were good!). The kits used LME and had grains for mini mash (is that the term?) for 20min. On first two I boiled (60min) 5 gallons and ended up with 3-3.5 gallons. On second one I added about 1/2 gallon. These two the OG and FG were around the values expected but not exact. Both beers as I said came out good and were gone quickly.
On my third brew I started with 6.25 gal and ended up with near 5 gal at the carboy. OG was spot on. So on my last brew I started with 6.5 gal. But this time I ended with about 4.5 gal at carboy. So I added 1/2 gal to the carboy. OG on this one was way off (1.032 vs 1.050 expected).
So y question is, to get the 5gal the recipe is for, is it better to start with more water so that at end of boil we have near 5 gal? Or is it the same if we start with 5-6 gal and just add water at the end in the carboy to get the 5 gal? Does it has any impact? Should I measure OG before adding water to decide if it is good idea to top off? What is the best way to get close to 5 gal at carboy? Or maybe a little more so the final is 5 gal on top of trub? Just in case I keg and do not bottle. Thanks.

 

[dlettow]

There are three main water loses to be concerned with.

First, the steeping grains that come with your kit will absorb about 0.125 gallons per pound.

Second, is your boil off rate. Boiling for an hour can boil off a gallon or more per hour, based on vigour of the boil and relative humidity. Your boil off rate will require a bit of trial and error to dial in.

Third is fixed amounts based on how much you lose due to leaving trub in the kettle and left in hoses. A half gallon is a good starting point for this.

Add up these three factors and you should be pretty consistent going forward.

 

[Alex4mula]

There are three main water loses to be concerned with.

First, the steeping grains that come with your kit will absorb about 0.125 gallons per pound.

Second, is your boil off rate. Boiling for an hour can boil off a gallon or more per hour, based on vigour of the boil and relative humidity. Your boil off rate will require a bit of trial and error to dial in.

Third is fixed amounts based on how much you lose due to leaving trub in the kettle and left in hoses. A half gallon is a good starting point for this.

Add up these three factors and you should be pretty consistent going forward.

Thanks. Yes the hoses too take some. But is it ok to always add water to the carboy to get to level? Or should I measure OG first? Will that evaporated water affect OG?

 

[dlettow]

Evaporation reduces the volume, but not the available sugars. So OG will increase as more boils off. If you take a gravity reading at the start of the boil and compare to the end, you will see a big difference.

If you ended with less than your 5 gallon target, take a reading and if your OG is higher than expected, feel free to add more water (boil it first to sterilize). If your OG is correct even with the low wort volume, I'd leave it. That means a different calculation was off.

 

[Alex4mula]

Evaporation reduces the volume, but not the available sugars. So OG will increase as more boils off. If you take a gravity reading at the start of the boil and compare to the end, you will see a big difference.

If you ended with less than your 5 gallon target, take a reading and if your OG is higher than expected, feel free to add more water (boil it first to sterilize). If your OG is correct even with the low wort volume, I'd leave it. That means a different calculation was off.

OK. That makes a lot of sense. The 1/2 gal I added was not boiled. Hope that doesn't cause problems. Thanks a lot!

 

[NGD]

OK. That makes a lot of sense. The 1/2 gal I added was not boiled. Hope that doesn't cause problems. Thanks a lot!

+1 to everything @dlettow said. Take a gravity reading before adding volume. It will help you determine how much to add. I’m bad at math so I cheat and use a dilution calculator.

https://www.homebrewsupply.com/dilution-and-boil-off-gravity-calculator

 

[NGD]

Also a suggestion. Try cutting your boil time in half with lighter beers and condense your hop additions. Should result is lighter colored beer unless the LME is old