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Boil Off Utility

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Danno6102

Brad,
I was just wondering how accurate the Boil Off utility is in the program. It seems like the gravity & volume calculations are simple, but I've never had them match. If I type in my preboil volume, the gravity, & the boil off, my OG is always different. I don't have my notes with me so I can't remember if it is usually higher or lower. Anyway, the reason I ask is that I am starting to use a lot of whole hops in my brews which absorb a lot of wort. Which will throw off your efficiency reading if you only measure the amount of wort gathered in the fermentor. So can I use the utility to give me an accurate measurement of how much postboil wort I actually have? Also, does the boil off utility take the cooling loss of 4% into consideration or does that still need to be subtracted out?

Thanks,
Danno
 
An example:

I enter my actual preboil volume (7.75g), I enter my actual preboil gravity (1.051), I enter my boil time (90), my OG into the fermentor was 1.071. What I do is adjust the boil off percentage until it gives me a gravity of 1.071, what I measured, & a predicted final volume of 5.54g. What I want to know is, can I take that final volume measurement to the bank?

Thanks,
Danno
 
Danno,
 The proper way to work this is to take accurate boil measurements (pre and post) when you are brewing an actual batch.  The issue is that the boil off percentage is unique to your equipment and conditions (for example altitude can affect it).  This one person might have 10% loss per hour while another might have as much as 20%.

 Next, it is best to work backwards - for example if you want 5.25 gallons into the fermenter, then set up your equipment settings so you have 5.25 gallons going into the fermenter, set up your boil % (measured above), and your other parameters.  This will let the software calculate the sparge water needed to hit your target volumes.

 As for the OG - once you have the equipment settings correct and have an accurate brewhouse efficiency (which also may take a few batches) you should be able to hit your predicted OG's consistently.   The only exception is high gravity beers which usually yield a much lower brewhouse efficiency.

 Here's a link to help you set up your equipment:
    http://www.beersmith.com/equipment_setup.htm

Cheers!
Brad
 
Let me rephrase my question. How accurate is the Boil Off utility if you know the four factors in the equation, pre-boil volume, pre-boil gravity, boil time & boil off %? How accurate is the "final volume" & the "final gravity" numbers it spits out?

Let me try to explain further & I hope I don't confuse you. I did calibrate my equipment prior to using it & filled in my equipment area properly. I have been using Beersmith with my old kettle with great success for some time now, so I know I've done this correctly. I did brew an actual batch on my new system. This batch had 12 oz. of whole hops in a 5 gallon batch. That's a lot of frickin' hops. When I calibrated my new kettle, it was draining all but 1 qt of water, so I added this into my water needed. I had 7.75g (1.051) wort pre-boil, I boiled for 90 minutes, & only ended up with 4g (1.071) wort in the fermentor. Obviously I did not boil down to 4g in 90 minutes. That would have given me a evap rate of 32% & an OG of 1.098, according to the boil off tool. So, that means there is a lot of wort still left in the 12 oz. whole hops. That wort plus the wort I collected is my actual final volume for accurate efficiency purposes, not 4g. I am trying to calculate that number from the known values I have, pre-boil volume & gravity, boil time, & final gravity. I have stated the values above. If I work backwards in the equation, are the values Beersmith gives me accurate? 19% evap rate & 5.54g final volume?

Thanks,
Danno



 
Danno,
 It appears when you are using the 12 oz hops you have much larger losses than normal in the transfer from the boiler to the fermentor.  I would probably include that larger loss in your "Loss to boil trub and chiller" figure.

 The separate "Boil off" tool does not include losses to trub/transfer, so you should probably subtract that number before using the tool.

 I hope this helps.

Brad
 
Well, Brad, that doesn't really help me. But I'm bound & determined to get this. The reason I am trying to figure this out is so I can estimate how much I am losing per oz of hops for future volume compensation & also for an accurate efficiency number. Like I said in a previous post, I got 75% eff into the boiler & if I used the 4g I got into the fermentor, my eff would have fallen to 55%, which is not right because there is another gallon or more left in the kettle soaked up in all those hops.

Let try again. I know that those 12 oz of hops absorbed a lot of wort, much more than 3 or 4 oz would have, but exactly how much is sort of what I am trying to figure out by calculating my evap rate & then my final volume backwards. More or less rearranging the factors in the equation.

One step at a time.

1) If I have my pre-boil gravity (1.051), my post-boil gravity (1.071), & my boil time (90min) can I calculate my evap rate?

Let's get this answered then I'll move on to question #2.

Thanks,
Danno
 
1) If I have my pre-boil gravity (1.051), my post-boil gravity (1.071), & my boil time (90min) can I calculate my evap rate?

The evaporation rate is simply the post-boil volume minus the pre-boil volume divided by the pre-boil volume.   The gravities alone do not determine the rate (though you might be able to back out the volumes from the gravity).

Lets pretend you had 6 gallons before the boil and 5 gallons after a 60 minute boil.  The evaporation rate would be (1 gal / 6 gal) or 16.67% per hour.

In your example, given only the gravities and the time you are missing at least one variable.  You need to know at least the starting volume, or the ending volume or the evaporation rate to finish your calculation (see the boil off tool).  Note that the ending volume would be the in-boiler ending volume and not include other losses due to trub/transfer.  Without at least one of these measurements, you can't accurately determine the others.

Cheers!
Brad

 
Brad,
I wasn't sure if you could calculate evap rate by how much the wort condensed.

I do have my pre-boil volume. 7.75g. So with that & my starting gravity & final gravity, I can calculate my evap rate?

I think we're getting close. ;D

Danno
 
Danno,
 I entered the numbers into the "boil off" tool and then played with the evap rate to match your final SG.

 I came up with an evap rate of 19% for a post-boil volume of 5.54 gallons.

 Now if you know what was actually transferred into the fermentor (volume) you should be able to calculate how much you lost to trub/transfer.

 One note of caution - I'm assuming you adjusted the OG and FG numbers for temperature.  If you did not, then you need to adjust them for temperature using the "Hydrometer adjust" tool first, then perform the calculation.

Cheers!
Brad
 
We got to the bottom of it. That's what I was trying to figure out, if I calculated backwards how accurate the final volume number would be & could I use that in some of my calculations.

Thanks Brad!

Danno
 
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