incomplete fermentation :(

[TheDecline]

Iv been having trouble getting my FG down to where it should be. I just did a Vienna Lager OG was 1.061 and after about 1.5 months of primary, diacetyl, secondary in a temperature controlled mini fridge, im at 1.036. That was with a 1.5L starter.

I dont know what else to do.

Proper fermentation temp to within a few degrees F
Aeration with spinny thing on a drill for a minute or so
Fair sized, obviously active starter

This has happened on a number of beers. I use a temperature compensated refrectometer for checking SG so I can only assume its correct. Destilled water reads 1.000 as it should. What am I doing wrong?

 

[Yooper]

I use a temperature compensated refrectometer for checking SG so I can only assume its correct. Destilled water reads 1.000 as it should. What am I doing wrong?

That would be an incorrect assumption.

Refractometers are great for prefermentation readings, but alcohol skews the reading greatly.

Check with a hydrometer.

Trust me.


There are supposed to be some calculators that can correct for alcohol in the sample, but I've never found one to be accurate. Those that like using a calculator to guess the FG have recommend the one at seanterrill.com- http://seanterrill.com/2012/01/06/refractometer-calculator/

Edit- don't forget to apply your wort correction factor as compared to a hydrometer vs a refractometer in those calculators as well!

 

[reverendj1]

Yooper +1. Refac before fermentation, hydrometer after/during.

You can however still use a refrac for ballpark guesses (after using the calculators) or to judge if fermentation has completed. Even though the SG will be wrong, it will still stay the same if fermentation has completed.

 

[TheDecline]

Alright im checking FG in a hydrometer now. I hate wasting that much beer each reading

I had no idea refractometers were so far off when alcohol is present. I guess it makes sense. In which case my OG readings are also off (albeit to a lesser extent) due to other stuff in the wort besides sugar and water.

Can anyone give examples of their wort correction factors they have discovered and for which refractometer?

 

[reverendj1]

Alright im checking FG in a hydrometer now. I hate wasting that much beer each reading

I had no idea refractometers were so far off when alcohol is present. I guess it makes sense. In which case my OG readings are also off (albeit to a lesser extent) due to other stuff in the wort besides sugar and water.

Can anyone give examples of their wort correction factors they have discovered and for which refractometer?

Refracs are accurate for OG, unless you are dumping a bottle of Jack in or something. It's just the alcohol that messes up the readings (at least to my understanding).

 

[Warthaug]

You cannot directly read a refractometer for final gravity readings - the presence of alcohol messes up the readings. You can, however, use one of many on-line calcualtors to correct for the presence of alcohol. The calculators are not perfect, but are close enough for 99% of home brewers. For example, using this one (and after converting your SG units to Brix):

http://onebeer.net/refractometer.shtml

Your OG of 1.061 (15 brix) & uncorrected FG of 1.031 (7.8 brix) gives you a corrected FG of 1.012; right about where you want to be.

Bryan

 

[adamj]

I take brix readings throughout the whole process and have no issues. Beer smith has a conversion tool built in to convert pre-fermentation numbers, as well as post. Just select the right one.

 

[Skarekrough]

Get another reading.

And there's no shame in re-pitching. Every year I do an Imperial Stout that pretty much needs that to get over the 1.040 hump.

 

[TheDecline]

Well the hydrometer reads about 1.011 which is exactly where I should be so im happy. Thanks for all the info everyone. This explains a lot.