[Kevin]

I brewed a coffee bourbon porter that failed to carbonate. It’s been a few months but I still have it bottled. It has great flavor so I’m not ready to give up on it yet. Has anyone ever tried to add the brew back to carboy, pitch yeast again, and rebottle?

[Bob357]

A number of years ago while still bottling I had a batch that didn't carbonate. I opened each  bottle and dropped a few grains of dry yeast in each bottle. Worked great. That would be a lot better than dumping them back in a bucket and adding yeast and who knows what else.

[Kevin]

That sounds much easier. How long did you let the yeast work before tasting?

[Bob357]

The beer sat at about 70 degrees F for 3 weeks before trying.

[Kevin]

Thanks much!

[Pope of Dope]

I hate to state the obvious, but you could dump all of it in a keg and force carbonate. 

[brewinhard]

I have had good luck with rehydrating a packet of dry yeast (EC-1118 Lalvin) and then using a sanitized syringe, quickly popping open each bottle and carefully injecting a little into each bottle then recapping with fresh caps.

This is all providing that you have added the correct amount of priming sugar already...

[Brotillery]

I got good carbonation out of the Muntons carb tabs back when I bottled. They take awhile to break down, it helps to crush them a bit.

[GRIMREAPER]

We opened up bottles and dropped a pinch of yeast in each.  Worked fine.  You can also get sugar tabs to drop in if needed.  Be careful with the sugar though.  Don't want overcarbs or explosions.

[Kevin]

To follow up, I added some yeast to each bottle and stored them for four weeks. The beer is carbonated and delicious!  Thanks for the advice!  Cheers!