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Consistently Missing Estimated Final Gravity

avcaudill

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Jan 21, 2019
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Hello all,

I desperately need some guidance!!!

I had been brewing extract kits for 10 years.  About a year ago I switched to all grain.  Since changing to all grain, I have yet to hit my estimated F.G.  I consistently miss from .010-.020.  For example, my latest failure was supposed to end at 1.011, but I'm looking at 1.028.  I've been researching this problem for months in an attempt to remove all the possible causes.  Below is the laundry list:

1. I bought a refrigerator and built an STC to maintain proper fermentation temperature control.
2. I changed from dry yeast to liquid yeast and I make a starter using a stir plate.
3. Bought a refractometer and assured it was calibrated with distilled water.
4. Bought a pH meter and assured it was calibrated per manufacturer's specifications.
5. In my journey to learn the value of proper pH, I started adding minerals to my water.
6. I also got a water report from the Municipality.

Here is my latest grain bill for my 5.5-gallon recipe:

Untreated water pH is 8.2-8.5
Mash pH was 5.2.
8lbs - Maris Otter
1lb - Crystal Malt 10L
8oz - Flaked Oats
4oz - Melanoidin
Imperial yeast - Independence (Mfr. Dec 18)
Yeast Nutrient with 15 minutes left in the boil.
Mash in - 150F for 60 minutes
Mash out - 168 for 10 minutes
60-minute boil
Pre-boil gravity: 1.050
Original gravity: 1.054
Gravity as of 20 minutes ago: 1.028

I pitched the yeast and it started fermenting within 6-8 hours.  The fermentation temperature was 63F for a week and I had strong fermentation with thick krausen for 3-4 days.  I still had active fermentation when I dry hopped one week after brewing.  I took a gravity reading after one week of fermentation and got 1.028.  It seemed very slow to me so I have increased the fermentation temperature 1.5F each day this week.  I'm currently sitting at 70F for a fermentation temperature.  I've been watching all week and I'm still seeing active fermentation via the airlock and I still have krausen being produced.  I can even see small particles churning inside, BUT MY GRAVITY READING IS STILL THE SAME AS IT WAS 5 DAYS AGO!   

I don't think the refractometer is the issue because I know I've been drinking rather weak beers (2.9-3.9ABV).  I'm clearly missing something and I would greatly appreciate any suggestions you have.  Thanks in advance!
 
Since you are using a refractometer, you need to adjust the reading to compensate for the alcohol.  Are you entering the gravity reading from the gravity scale on the refractometer or are you using the brix conversion on the session tab to enter in the final gravity?
 
Oginme said:
Since you are using a refractometer, you need to adjust the reading to compensate for the alcohol.  Are you entering the gravity reading from the gravity scale on the refractometer or are you using the brix conversion on the session tab to enter in the final gravity?

Holy crap, I love the beersmith community!!!  I didn't know I had to adjust the reading to compensate for the alcohol.  I've dredged through hundreds of forum topics and compensating for the presence of alcohol has never come up.  Although, I am very grateful that I learn a number of other things. 

I am reading from the gravity scale on the refractometer.  Using the brix scale is something that I haven't learned yet.  So, how do I compensate for the alcohol on the refractometer?

 
Refractometers are calibrated to read sucrose concentrations in water.  We use them for measuring maltose in water.  The refractive index of sucrose and maltise is pretty close, so in water/sugar solutions the gravity scale is close enough for general use.  The Brix scale is much more accurate, being a wt of sugar to wt of solution measurement.

Once the wort starts fermenting. The alcohol in the solution throws the scales off since alcohol has a much lower specific gravity than water. 

To compensate for this, take your Brix reading and the OG of the wort and plug those into a refractometer tool, such as the one found in BeerSmith.  You must set the type to 'fermenting wort' for the calculator to compensate for the alcohol content.

Even easier, Brad included the automatic conversion on the 'session' tab in the recipe file.  Next to the input for final gravity, there is a refractometer icon.  Click on this and the tool will pop up and use the OG reading from that recipe to adjust the gravity conversion for the alcohol content.
 
with a brix of 7.2 (i'm guessing here from your post...) and an OG of 1.054, you should be looking at a FG of 1.013, which is around 5.5% ABV
 
Even though there are calculators to adjust refractometer readings post fermentation I still use a hydrometer to compare against.
 
It is always best practice to calibrate your refractometer by zeroing it with distilled water and then using the refractometer tool in BeerSmith to calibrate it against at least 1 dependable hydrometer reading.  Like Kevin58, I always use my precision hydrometers for measuring OG and FG on standard batches.  Having this calibration, I can cheat on smaller batches and just use the refractometer for OG, though I still use the hydrometer for the FG reading.
 
It appears that the only variable that I have been unable to change was removing myself from the equation.  I figured I was the problem.  I converted the brix reading to specific gravity and learned that I'm down to a F.G. of 1.012.  I am very thankful to everyone who responded and provided me with yet another valuable lesson. 
 
Cheers to learning! I try and learn something every brew, and i've been brewing for awhile, and brewing a lot!
 
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