[cheba420]

Looking for some insight here. I'm pretty sure I understand what happened, just not sure HOW it happened. I brewed an IPA today. My pre boil target gravity was 1062 and PB volume was supposed to be 7.5 Gallons. I was shooting for a 6 gallon batch into the fermenter. I wound up with a PB gravity of 1059 but had put 2 extra quarts of sparge water in the mash tun and wound up leaving it in the tun when I reached 7.5 gallons in the kettle. I assume that had I not used that extra 2 qts, I would have nailed my PB gravity. Oh well.

Heres the issue. I wound up with 4.75 gallons of wort into the fermenter. I left about a quarter gallon of cold break behind in the kettle. Since I started at 7.5 gallons and lost .25 gallons to the cold break in the kettle, this means that I boiled off 2.5 gallons in the 90 minute boil or 30% of the total volume. My boil was slow and steady. This was not an agressive boil by any means. Doesnt this seem excessive? My OG after cooling was 1072 which was my target which further confuses me. Seems like it would be a little higher than that since I concentrated my wort down to 4.75 G.

Any ideas here to get my evaporation under control? Or should I just be starting with more volume. Any pointers would be helpful.

[tschmidlin]

You need to include the quart you left behind in your calculations, so it is 5 gallons at 1.072 to finish.  You can calculate the efficiency using 4.75, but for predicting the gravity after the boil, that 0.25 gallons counts.

That does seem like a lot lost for a 90 minute boil, I assume you are confident in your volume measurements?

[bluesman]

How are you measuring your kettle volume?

2.5 gal of volume lost in 90 min equates to roughly 20% evaporation rate/hr. which is very high.

[weazletoe]

Let's all just assume he's boiling with a Pratt & Whitney jet engine. Doesn't seem excessive then, does it? 
 Now letys say it's a regular banjo burner.....What's the diameter of your pot, and how's the humidity where you live? I noticed when I moved from Ohio (which is typically like a rainforest) to Idaho (a desert) my evaporation has gone way up. I'm pushing the 20% mark. In fact, my last batch came in about 2 gallons shy of my 10. I need to make some changes to my calculations.

[narvin]

What's the diameter of your pot, and how's the humidity where you live?

I'd look at these two factors... 20% is not necessarily high with a wide pot.

It's also not very useful to look at evaporation as a percentage, in my opinion.  For a given pot shape/size, you'll boil off the same volume in quarts whether the pot is holding 5 or 10 gallons, assuming the boil vigor is the same.

[tomsawyer]

I think theres something else going on here.  You say you had 7.5gal of 1.059, that is 443 points of sugar.  You wound up with 5gal at 1.072, thats only 360 points.  You don't lose sugar from boiling.  Which means that one or the other of your volume measurements was off, or one of your gravity measurements.

Do you take into account the fact that grain absorbs 0.125gal/lb?  Maybe you didn't drain out 7.5gal in the first place.  For a grain bill to produce 7.5gal a 1.062 gravity wort you probably had around 17lbof grain right?  That means it on to held a little over 2gal of water.  I'm guessing you had 5.5gal preboil, making 4.5gal post-boil quite normal.

[cheba420]

Sorry, Gentlemen. I guess I should have provided some more information. I use a standard turkey fryer type burner. My kettle is a sankey keg and I measured everything a couple of times yesterday because I didnt trust the numbers.

I have a measuring stick that I've marked for every half gallon in my kettle so, I know I had 7.5 g to start my boil. I'm in Phoenix, AZ and it was 100* yesterday...no humidity....but thats normal for this area. I measured my post boil volume with the marks that I have on the side of my carboy. So, I know theres accuracy there. My hydrometer is on point and I checked the temp of the sample. Again, on point.

Is this all evap? I've read several times that 9-12% is standard. Can my hot, arid weather be the culprit? I think Tomsayer has a very valid point. Seems as if something else might be off. I should have wound up putting 6 G in the fermenter and I only got 4.75. If you boil a wort down that low, shouldnt my OG been much higher due to the concentration??
Thanks for the replies.

[tomsawyer]

7.5gal at 1.059 should produce 5gal at 1.088.  Since you volume meaurements were accurate, your gravity readings must have been off somehow.

How many pounds of grain was in your grist?  Do you know what your average efficiency runs?  That'd give us a clue as to which gravity measurement was off.

[cheba420]

7.5gal at 1.059 should produce 5gal at 1.088.  Since you volume meaurements were accurate, your gravity readings must have been off somehow.

How many pounds of grain was in your grist?  Do you know what your average efficiency runs?  That'd give us a clue as to which gravity measurement was off.

Lennie, Thanks for the feedback. How did you go about calculating that? Its interesting and I think it would help me tremendously if I understood how you came to that equation.

Grain bill; was 18.37 lbs. My efficiency runs 65-70%. When I take my hydrometer samples, I cool them to 60-70* before I take the sample. My hydrometer is calibrated to read @ 60*. My sample was @ 70 so I added one point. PG gravity read 1058 and I added 1 to get 1059. At the end of my boil, I pulled another sample and cooled it down to 70* and it read 1072, I added 1 so 1073 with the temp adjustment.

I think it should also be known that I'm using beer smith. So, when I enter my recipe and the program tells me I should have 1059 pre boil and 1072 post boil and thats what I come up with BUT the final volume is shot.....Just not sure how to correct this and its pretty frustrating. Thanks for the help.

[bluesman]

What's the diameter of your pot, and how's the humidity where you live?

I'd look at these two factors... 20% is not necessarily high with a wide pot.

It's also not very useful to look at evaporation as a percentage, in my opinion.  For a given pot shape/size, you'll boil off the same volume in quarts whether the pot is holding 5 or 10 gallons, assuming the boil vigor is the same.

Evaporation rates are useful for targeting final volumes per time unit and can impact energy consumption.

cheba420: How much water did you add to the mash tun? Have you recently calibrated your hydrometer? How much wort did you leave behind in the mash tun?

[tomsawyer]

I do it as follows:  1.059 is 59 points per gallon (ppg, a measure of sugar per gal).  You had 7.5gal of this, 7.5 x 59 = 442 points total (the total amount of sugar in the pot).  Then you boiled and got 5gal, so the new ppg is 442/5 = 88ppg (back to sugar per gal).  This means the gravity post-boil should have been 1.088.  You got 1.073.  Boiling doesn't cause sugar to disappear sugar so some measurement is wrong.  If your hydrometer was not reading right, I suppose that could cause the discrepancy.

You had 18.4lb or grain.  18.4 x 36 points per pound per gallon (ppppg) is around 662 points of sugar.  I used 36ppppg just as an average for base malts and specialty grains.  We'll use the low end of your efficiency since big beers generally give lower efficiencies.  662 x 0.65 = 430 points.  Now divide by 7.5gal and you get  57ppg or 1.057.  Thats close to what you saw.  If we divide the 430 by 5gal, you'd have seen 86 ppg or 1.086, which is higher than your post-boil measurement.  This suggests your postboil gravity measurement was wrong.  Maybe you read it was 73 but it was really 83.

For your grain bill to match the post-gravity reading, you would have to have only gotten 55% efficiency.  This is certainly possible with a big beer since more grain holds more water and that water has sugar in it.  Plus you diluted with more water and didn't collect it (why? boil longer).  I don't know if you brew a lot of beers with gravities like this, if you know your efficiency is 60% for a big beer then recheck your gravity.

Can you tell I'm bored here at work?

[bluesman]

Can you tell I'm bored here at work?

Really? 

[cheba420]

 
cheba420: How much water did you add to the mash tun? Have you recently calibrated your hydrometer? How much wort did you leave behind in the mash tun?
[/quote] Ron, I dont have my notes in front of me but I'd have to say it was 9.5 -10G. I accounted for the grain absorption. I have not calibrated my hydrometer. Didnt know you could. Just took that tool for what it was and trusted it. I assumed because its not mechanical, that it couldnt be adjusted. However, I now realize that it can be compensated for. Check it in plain water to get a read??? I left about 2 qts of wort in the tun.

I do it as follows:  1.059 is 59 points per gallon (ppg, a measure of sugar per gal).  You had 7.5gal of this, 7.5 x 59 = 442 points total (the total amount of sugar in the pot).  Then you boiled and got 5gal, so the new ppg is 442/5 = 88ppg (back to sugar per gal).  This means the gravity post-boil should have been 1.088.  You got 1.073.  Boiling doesn't cause sugar to disappear sugar so some measurement is wrong.  If your hydrometer was not reading right, I suppose that could cause the discrepancy.

You had 18.4lb or grain.  18.4 x 36 points per pound per gallon (ppppg) is around 662 points of sugar.  I used 36ppppg just as an average for base malts and specialty grains.  We'll use the low end of your efficiency since big beers generally give lower efficiencies.  662 x 0.65 = 430 points.  Now divide by 7.5gal and you get  57ppg or 1.057.  Thats close to what you saw.  If we divide the 430 by 5gal, you'd have seen 86 ppg or 1.086, which is higher than your post-boil measurement.  This suggests your postboil gravity measurement was wrong.  Maybe you read it was 73 but it was really 83.

For your grain bill to match the post-gravity reading, you would have to have only gotten 55% efficiency.  This is certainly possible with a big beer since more grain holds more water and that water has sugar in it.  Plus you diluted with more water and didn't collect it (why? boil longer).  I don't know if you brew a lot of beers with gravities like this, if you know your efficiency is 60% for a big beer then recheck your gravity.

Can you tell I'm bored here at work?

Lennie, Thanks for the breakdown. That is extremely helpful. I've heard a lot of people discuss gravity points but not in that context. Again, thank you. I cant say that my efficiency is any certain number with a big beer. I didnt really think of efficiency as fluctuating depending on og. Thats some food for thought as well. Sounds like I may have to check my hydrometer and see if thats the issue.

Theres another issue as well.....thats my boil off. The way I calculated it I get a 33% evap rate. Or 1.66 G per hour. That just cant be normal, even in Phoenix. Does this mean that I have to adjust my recipe as well as my mash/sparge water to end up hitting my targets??

[morticaixavier]

to calibrate a hydrometer get some distilled water. that should read 1.000 at 60 degrees.

[tubercle]

If the hydrometer is off shouldn't it be off the same throughout the scale if all else is constant (sample temp, etc...)?