Beer finished high. Starter or Rehydrate dry yeast to finish fermentation?

[HomebrewingDNA]

I underpitched a high gravity beer and the yeast dropped off at 1.027, while it should have been more like 1.015-1.010. It's been sitting at this reading for at least a week. I have another 11g of the same dry yeast. Should I make a starter with it or just rehydrate? I know that making a starter with dry yeast is not recommended, but is the lack of oxygen in the wort going to play a role if I only rehydrate?

Edit: Also, say I don't care that the beer finished high. Should I expect bombs if I bottle with priming sugar?

 

[mredge73]

Don't add any more yeast, you should have plenty.
There is no O2 in the wort for new yeast to propagate and you don't want to add O2 at this point.

Warm it up a little (no more than 70-72F) and gently stir it up to get the yeast back into solution.
This should allow it to drop a few more points, however it may not go lower than 1.02 if this is an extract batch.

As far as bottle bombs are concerned, I would worry more about it not carbonating enough.
If the yeast are too full to finish the main course, they aren't going to want to eat dessert.

 

[jurgenph]

any details on recipe? OG? yeast used? temperature?


J.

 

[HomebrewingDNA]

I followed this recipe to the T. I hit all my numbers and have been fermenting at about 18 C for oer 40 days now. I pitched 11g of rehydrated dry yeast.

Edit: My plan was to make a starter with another 11g of dry yeast and transfer the wort on top of it in a new fermenter and harvest the old yeast. After reading up online some questions turned up though. Hence, my initial post.

 

[STMF]

It needs to be asked, are you using a refractometer?

 

[HomebrewingDNA]

Yes, I am.

 

[bajaedition]

Yes, I am.

use a hydrometer once beer is fermented.

 

[Yooper]

Yes, I am.

There's the problem.

Refractometers read the refraction of light in a sucrose solution. Pre-fermentation, it can be close enough (our wort is mostly maltose), especially if a wort correction factor is done as part of the conversion.

Once alcohol is in the solution, the refraction of light is skewed, and the reading is not accurate.

There are conversion tables out there that can help, but they are not always very accurate (particularly if you don't know your own wort correction factor). I always use a hydrometer when fermentation has begun (or ended), but if you want to guestimate the FG using the refractometer, you can try this conversion: http://seanterrill.com/2012/01/06/refractometer-calculator/

 

[HomebrewingDNA]

Thanks guys. I just got the refractometer and I was not aware of this phenomenon. I'll use my good old hydrometer as soon as I get home from work. I tried using the table and it tells me fermentation is done, but I honestly have no idea what I'm doing there.