Low Volume after boil

I have had a real challenge with the amount a wort that ends up in my primary after the boil and cool down. I have a 15 gal. brewpot and a 10 gal. mash tun. I don not like to add any make up water to my wort before or after the boil. I like my beers to be higher in ABV rather than lower, so I try not to add any make up water. I usually mash with 18-20 qts. of water( 1 1/2 qts. per lb.). I have used up to 6 gals. of sparge water because I try to have 8-8 1/2 gals. of wort before I start the boil. I will sparge till my refact. reads 1.010.
    I like to have a good rolling boil and I keep my boils to 60 min. all though I would like to extend that time for certain beers, but I know  I will come up even shorter for those brews. As I said earlier I use a 15 gal. brew pot made  by Polar, and I live in Wyo. at an elevation of 5000 feet. I don't know if I loose so much of the wort to evaporation because the pot surface is so large combined with the higher altitude or what, but I always come up short by 2-3 qts. of my 5.5 gals. target. I have tried partially covering the pot with the lid to reduce some of the evaporation as well as slowing down the boil. ANY help or insight to my dilemma would be greatly appreciated. Thanks! 

The altitude means you boil at a lower tmeperature - about 203 F in your case.  But your boiling rate (how much heat you are putting into you wort) controls how fast you evaporate.  If you start with 8.5 gal of wort and end up with 5 gal after boiling you are boiling off 3.5 gal - that's a lot.  I boil off about half that much.  Try a slower boil rate.  It will also save gas/electricity.

Agreed.  Plus, sparging down to 1.010 may maximize your lautering efficiency, but you are also diluting your wort with every extra ounce collected that is that weak.

Perhaps try hitting the boil volume and the target pre-boil gravity and boil less violently.  Not sure, but boiling off 40% of your wort may be affecting your flavor too. 

I'm interested in this also. I'm brewing at 6800 ft, and have two 5 gal brew pots. My boil temp is right at 200 deg. I have to dial down the boil volume just so as not to over flow the brew pots. I hold my wort  just below a boil, simmering rapidly? I have been wondering how this affect my evaporation rate, and my hop utilization. I just did a 90 min boil on my last batch that started at 9.5 gal and boiled down to 6.5 gal into fermenter. Some loss is due to hops, the rest is evaporation. :

I couldn't find any quick info via Google.  Suppose the lower air pressure could accelerate evaporation, but dunno the science there. 

I would think the vigor of the boil and the shape of the boil vessel and surface area would be bigger factors than air pressure. 

I'm quite positive it's a matter of surface area, which you've got a ton of.

I start with 7 - 7.5 gallons (don't know for sure as I measure by the handle rivets) in a D battery shaped 9 gallon brewpot , boil as vigorously as I can without making a mess for 60 minutes, and finished with 6 gallons on the nose last batch.

You're doing five gallon batches in a pot designed for double.

Perhaps max out your mash tun, boil it all, keep two primary vessels on hand, and see what you can get?

So just to help me understand this issue, is the primary purpose of the boil to condense the wort by evaporating the water?

"Primary purpose......."

I would say no, the primary purpose is to sanitize the wort, isomerize the alpha acids for bittering, and to adequately burn off any DMS created, etc.

A secondary outcome is the concentration of the wort.  I imagine if brewers could eliminate the uncertainty and always know exactly how much they'd have post-boil, they jump at that option.

Maine is right about the surface area, especially if the pot is short and wide, which I think the 15 gal Polarware is. 

MaltLicker said:

I would think the vigor of the boil and the shape of the boil vessel and surface area would be bigger factors than air pressure. 

Click to expand...

Yes, its the shape of the vessel and the rate of application of heat.  The atmospheric pressure just determines at what temperature boiling occurs.  As you reduce the pressure, it takes less heat to reach the boiling temperature.  The more surface area available, the more evaporation can occur.  So the two factors combined are causing a higer evaporation rate.

I'm not sure the level of concentration would affect the flavor as the temperature is actually lower.

I brew in Colorado along the front range, so my elevation is around 5100 ft. I too get a lot of evaporation. I agree that the boil pot geometry is a contributing factor in the evaporation, but there are other variables as well that may be nearly as significant. I make 5 gallon batches using a 10 gallon boil pot. It's pretty square (diameter/height). The amount of air flow you have around your boil pot will also significantly affect evaporation rate. I used to brew in my garage (when it was warm out) and just moved to my basement (next to an open window) and indeed I saw less evaporation in my basement compared to what happened in my garage. I suggest you adjust your recipe so that you either start with as much water as you can and boil it down to your desired volume or you reduce your target post boil wort volume. This way you can have the vigorous boil you need to get good hop isomerization (you only need to boil for 10  - 15 minutes for sanitization) As I understand it, you really want that vigorous boil for hop utilization, especially if you are making a high gravity beer (which hinders hop utilization) and you want some hop bitterness too.

I brewed in Ogden Utah for 4 years, I think the less dense air/drier air has an effect on the evaporation.  I would suggest keeping the boil rolling and not to simmer, or you won't volatilize Dimethyl Sulfide, a malt compound formed at temps above 180 F.  DMS tastes like creamed corn.

Today I brewed my ag version of  Sierra Nevada Pale. I kept the above info. in mind, (thanks all;D). I started with 7 gals of wort split between two brew pots and did a full rolling boil for 60 mins. There was a lot of hops in this so I didn't reduce the boil temps. I ended up with 4.75 gals of wort with a higher gravity than I was aiming for. I added a 1/2 gal of water into the fermenter which brought the gravity back in range and I ended up with 5.25 gal into the fermenter. All in all a very successful brew day!

Thanks for all the input. It sounds like my suspicions were correct about the rate of boil and the configuration of my brew pot. I'll make the adjustments on my next brew. Thanks to all and have a great holiday season!                            Cowboy Up!