Fix under-pitched keg beer

Australia & New Zealand Homebrewing Forum

Help Support Australia & New Zealand Homebrewing Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

adzr

Member
Joined
27/11/13
Messages
20
Reaction score
1
I recently brewed a porter using a kit / partial mash technique. All went well except I messed up the yeast and didn't put enough in. As a result, it went from an OG of 1.050 to a FG of only 1.022. I went ahead and carbonated the beer in the keg to try it anyway. It is not very nice at all.

I would like to save the beer if possible, but not sure that given it's been carbonated for a number of weeks now, and has been sitting at 3 Deg C in the keg, if it is possible. I thought about racking it back to a fermenter, warm it up back to 18-20 Deg C and pitch more yeast. Does anyone know if this will work or have any other idea? How much extra yeast would I pitch? And would the beer need to lose all of its carbonation before pitching more yeast?

Thanks.
 
I think you've not got going to have much luck but can try something along the lines of

pull keg out and leave pressure valve open, for a few days

try to de carb it.

you cold then try adding more yeast

then wait a while, then transfer keg to keg (ideally bend up you out tube if you don't have one you can trim)

Then carb up and see.
 
How do you know it wasn't finished/ stalled or under pitched? Strong dark beers often finish high what were the ingredients? mash temp and strain of yeast can also affect FG. It may taste like poo because of poor process or bad recipe.

Is your hydrometer calibrated? How long has it conditioned?

I'd just let it age in the keg and go back to it in six months the yeasty beasties will eventually do there job or at least improve it enough to drink
 
Draw a sample into a hydro tube. Stick add some yeast and a hydrometer and cover.

See if the fg drops.

This is called a forced ferment and will tell you where the FG Of your main batch *should* finish
 
Thanks for the suggestions guys.

TheBigD - From the information I had, the FG should have been a lot lower than 1.022. My process was fairly straight forward, done it before and never had a problem, so I doubt it was process. What I do know is I didn't rehydrate the dry yeast properly, and a lot of it was stuck on the glass after pitching. I couldn't get it off, so I probably only put in 3/4 of the yeast packet. So I'm 99% sure my problem lies with the lack of yeast. It had conditioned for a good 6-8 weeks, more than what should be enough. I don't really want to hold up a keg for 6 months on the small chance the beer becomes "drinkable".

Stux - That's a good idea. If I did that, how much yeast should I put in to the sample tube? And if it turns out that the SG is dropping, suggesting further fermentation to the main batch is necessary, how much yeast should I put back in to the batch? I assume I would have to warm it back to ale fermenting temperature and let it go flat again? Would leaving it carbonated effect the fermentation process?
 
The idea with a forced ferment is to put plenty of yeast in, just to be sure ;)

Ideally, it would be the same yeast so you have the same attenuation profile, but it doesn't have to be. So perhaps a good opportunity to use up a spare coopers yeast you have sitting in your fridge/cupboard. Also, temperature control is not important. You're not trying to make beer, you're just trying to see where the beer will get to given a healthy pitch.

Re the re-fermentation, I'd use a full pitch. Also, quite possible the beers characteristics are already set, so maybe you don't even have to use the same strain.

Re de-carbing, I'd pull the keg out, let it warm up, shake it a bit, let the gas out (till it gets wet ;)), then shake again a few minutes later and repeat. That should get it plenty de-carbed. It won't need to be totally de-carbed, as a normal fermenting beer will be slighly fizzy anyway (depending on airlock pressure I think)

Kaiser's wiki is down so here is a link to an archived version of his page on Fast/Forced Ferment Tests

https://web.archive.org/web/20141103091615/http://braukaiser.com/wiki/index.php?title=Fast_Ferment_Test
 
mxd said:
I think you've not got going to have much luck but can try something along the lines of

pull keg out and leave pressure valve open, for a few days

try to de carb it.
I strongly don't recommend doing that. Leaving the pressure valve open allows air to get it, and quickly oxidises the beer. Have you done this? I've been unfortuante enough to have 2 kegs deplete on me and it only took one day in the fridge to ruin it.
Stux's method would be safer.
 
+1 for the forced ferment test. I doubt the 56% apparent attenuation you achieved was the intended result, but you’ll have a much better idea if you complete the test.

Assuming the FG drops by more than a few points, I’d pitch more yeast – probably a fairly neutral strain like US05, or just more of the original, but properly rehydrated this time. I’d let the keg warm up to 18C or so, relieving pressure periodically, then carefully rack to a fermentor and pitch the yeast.
 
Thanks for the help guys. I have decarbed the beer as per stux's recommendation. Now need to get some yeast and take a small sample and see if the SG drops.
 
Back
Top