O.G. Higher Than Expected...I'm Confused

[jerryalan]

Today I brewed a 5.5 gallon Dunkelweizen and expected to get a starting gravity of 1.058 but ended up getting 1.063. I used the following grain bill:

7lbs German Wheat (potential: 39)
4lbs 2-Row (potential: 36)
1.5lbs Caramel Wheat (potential: 35)
1lb Caramel 40 (potential: 34)

Pre-Boil Volume: 7.22 gallons
Pre-Boil Gravity: 1.044
Post-Boil Volume: 5.5
Post-Boil Gravity: 1.063

I mashed with 1.27 quarts of water at 154 degrees per pound and sparged with a little over 4.25 gallons at 170 degrees (the reason for 1.27 per pound was because I forgot to add .25lbs of chocolate I had in the recipe). I had to do a second sparge because my original pre-boil volume was only 6.5 gallons. Temps were held with a RIMS tube and the pH was 5.6.

My pre-boil volume was 7.22 gallons and the gravity was 1.044. Based on the potential yield numbers from BeerSmith and the Malts Chart, that's 63.1% efficiency (I have a 65% brewhouse efficiency that could probably be improved with a better crush).

To calculate my predicted post-boil starting gravity I multiplied 44 and 7.22 (pre-boil volume) to get 317.68. I then divided 317.68 by 5.5 (post-boil volume) and got 57.8 for my predicted starting gravity. However, my starting gravity ended up being 63. The refractometer is properly calibrated with distilled water.

Did I mess up on my calculations somewhere?

 

[BBL_Brewer]

This is a hard question to answer confidently. You seem more than competent with the math and the process........so your guess on the matter will likely be better than anything we could point out. If you have a hydrometer try using that to double check your refr readings. One question though, did you chill the wort sample to the same temp of the distilled water that you used to calibarate? I have a refr and I figured out before using it that the distilled water and the wort sample need to be same temp when taking readings. This could have perhaps thrown off your calcs. The only other thing I can think of is maybe you were off on your volume measuements but you sound pretty with the program..............bout all I can think of off hand.......hope this helps you brainstorm a little.

Cheers

 

[smarek82]

This has happened to me the past 2 brews(once I started calculating after reading an issue of BYO), usually calculating the FG lower than the actual reading. I use a properly calibrated hydrometer.

My only solution to the problem was incorrect volume measurements. I don't have sight glass, I just used gallon jugs poured in my pot and have lines on my mash paddle.

It looks like you would have had at least a 1/2 gallon incorrect measurement(on pre-boil or final vol) to be off by 5 gravity points, which most likely is not the case.

I'm interested to see if anyone has another idea on this topic as well.

 

[broadbill]

Your calcs are correct.

Either its incorrect volume measurement or incorrect hydrometer reading (did you correct for temps on the hydrometer reading?)

 

[smarek82]

First guy, jerryalan, was using refractometer and my wort temp was 60degF so no need to correct. So yes, most likely volume.

It seems like his equipment is fine-tuned unlike mine. So the mystery goes on!

 

[jerryalan]

I'll double-check my sight glass markings to ensure that they are correct. I marked them in half gallon increments a while back but maybe I was off. That's the only thing I haven't yet checked. The refractometer has automatic temperature correction but I still let the wort cool a bit in the pipette before reading.

Maybe the brew gods tossed in some DME when I wasn't looking.

 

[Photopilot]

How many times have you brewed with this setup? As you said 65% is not a very high efficiency, you have a lot of room for improvement in that area. It sounds like you are methodical in your process, yet somehow you managed to squeeze out some efficiency on this batch or a measuring error occurred somewhere.

Some thoughts. Do you crush your own grains or do you buy it crushed? Maybe your source changed the gap, or your gap moved? Did you take multiple samples to crosscheck your OG?

 

[broadbill]

Some thoughts. Do you crush your own grains or do you buy it crushed? Maybe your source changed the gap, or your gap moved? Did you take multiple samples to crosscheck your OG?

I'm not sure grain crush as anything to do with this. His issue is that he calculated an estimated OG based on a volume and pre-boil gravity, but his actual OG was much higher.

A change in crush would have been reflected in a higher pre-boil gravity and a better brew-house efficiency (this batch was 63%, close to his average of 65%, so there is some consistency there).

 

[jerryalan]

How many times have you brewed with this setup? As you said 65% is not a very high efficiency, you have a lot of room for improvement in that area. It sounds like you are methodical in your process, yet somehow you managed to squeeze out some efficiency on this batch or a measuring error occurred somewhere.

Some thoughts. Do you crush your own grains or do you buy it crushed? Maybe your source changed the gap, or your gap moved? Did you take multiple samples to crosscheck your OG?

I've probably brewed about five batches on this system so far. I take two samples for each test just to be sure I'm getting the proper readings. I do crush my own grains and I'm sure my roller gap is the cause for poor efficiency (either that or my water profile). I don't think the crush would be the culprit though. My readings were taken pre-boil to calculate what the starting gravity would be.

 

[BBL_Brewer]

This is for smarek82 mostly but all could benefit.......I too have had some discrepancies in the past calculating gravity down the line. I have developed my own microsoft excel based software to cut down on my calculator time and I have incorporated changes in volume due to thermal expansion. Basically my software calculations are thermally balanced. Lets say preboil you take a gravity reading. It's 1.040. You measure 6.7 gallons. So, the straitforward math would be 6.7 x 40 = 268 PPG. 268/5 ~ 1.054 rounding up for the calculated OG. But, what you don't realize. Is that the 6.7 gallons that you measured is at one temp.....say 130 maybe after a mash.....and the 5 gallons that you have at the end of rainbow is chilled to 68. This creates discrepancies due to changes in density due to water temp which in turn causes a false volumetric reading that gets plugged into the equations. Do some reading on the net on changes in volume due to thermal expansion and you'll see what I'm getting at here. Hope this helps some folks fine tune a little.

Cheers

 

[smarek82]

What formula did you use in your excel file?

It does make sense BTW

 

[BBL_Brewer]

Here is a link that gives some background, the formulas, and a calculator that might come in handy.....if you have anymore detailed questions on how to apply this let me know. Also, anyone that wants to correspond by messaging feel free. I don't have many people to talk brew with around these parts.

http://www.engineeringtoolbox.com/volumetric-temperature-expansion-d_315.html

Cheers

 

[smarek82]

Sounds good to me, thanks for the info. I'm at work, so I'll have to review it when I get home.