View Full Version : Stuck Fermentation

02-25-2014, 02:22 PM
First, ingredients:

1.44K Chestnut Honey
2.3L spring water
1L Pressed apple juice
1 Tsp Yeast Nutrient
3mg Thiamine (Vitamin B1)
2 Tablespoons Malted Yeast Extract
3 tea bags
200g Black Currants
Muntons/Gervin G4 (Alcohol tolerance 21%)
Starting SG 1.09

The above recipe initially made for a quick and smooth fermentation, SG dropped about 80 points in less than two weeks. I racked to the secondary and decided I wanted something stronger than the 11/12% that I think this worked out at (the mead calculator was working at that time). I decided to add 0.5 kilos of honey to the secondary (heated with a little spring water and left to cool), expecting fermentation to flare up. It didn't. I left it for a few days and took another SG reading which came out at 1.04. There seemed to be fermentation because there was around 1 bubble every 45 seconds, but not what I'd expect from half a kilo of honey.

Yesterday I decided to re-pitch with K1-V116 because its an all rounder and quite tolerant. It's also much cheaper than the G4. I re-hydrated in some honey water, left for 30 mins until it was fizzing and foaming away and added to the stuck ferment. It's now been 24 hours and the must is as (in)active as it was prior to the re-pitch. I even added another tsp of nutrient and another 2mg of B1 but this did not help. Sorry for the long post - any ideas?

02-25-2014, 03:46 PM
Just chucking in the extra yeast wouldn't necessarily restart or increase the fermentation.

You'd need to look up, I think the phrase is "acclimatised restart".

On smartphone so too long to try and type it in, but a quick search should provide the method.

The other thing to watch with meads is pH swing (downwards). It's most frequent with traditionals but can happen with batches that have some buffering ability (which I suspect yours has). Mid-3 is the sweet spot, 3 and below can slow or stall. Potassium carbonate is the trick for that......

02-25-2014, 04:14 PM
I believe that fatbloke has your problem pegged; I'm suspicious of pH in this case, given your recipe. The black currants will drop pH through the floor in any must that isn't sufficiently well buffered. If you cannot get hold of a pH tester, or pH strips, then I'd recommend that you try adding a tsp of potassium carbonate (or potassium bicarbonate - their effect would be nearly identical in this case) to improve the buffering potential of the must before you pitch. Also, by all means, attemperate your rehydrated yeast to the must before pitching.

02-25-2014, 04:52 PM
Thanks for your help, fellas.

02-25-2014, 06:03 PM
Thanks for your help, fellas.

If after you have adjusted the pH the fermentation does not restart one thing you might do (and I don't know if this is what Fatbloke was suggesting) is to create a starter for your yeast (I might use a 1/2 C of apple juice to which I might add nutrient and energizer AFTER the fermentation has started) ) and then after about 8 hours of active fermentation I would pour a 1/2 cup of your stuck fermentation into the starter. (NOT the starter into the stuck fermentation!) If the starter continues to be active add another cup this time from the stuck mead (so you are doubling the volume of the starter). After another 8 hours I would add 2 C. Repeat by adding 4 C after another 8 hours and then add 8 C after yet another 8 hours. You can then add the starter to the rest of the stuck fermentation.
The idea is that you gently acclimatize the new yeast to a low pH high alcohol environment slowly...

02-28-2014, 10:05 AM
Further to this, I just removed a small amount of must from the ferment to mix with the potassium carbonate, just to test what it would do; the must/potassium carbonate mix turned very dark and gave off a strong smell of peroxide. Is this normal, something to do with hydrogen being released from the must?

02-28-2014, 11:18 AM
That doesn't sound quite right to me. Every time I've mixed potassium carbonate or bicarbonate into a mead, there is a little bit of fizzing (byproducts of the reaction with organic acids are usually just water and CO2), and no color change.

Are you sure you got pure carbonate, and not something else?

02-28-2014, 11:31 AM
I definitely ordered potassium carbonate from Fast Chem via eBay. I've since read that K2CO3 makes wine musts darken a bit but subsequent fermentation will take care of it. In regards to the smell, having thought about it it was less a smell and more a kind of 'harsh' feeling in my nose... CO2 perhaps?

03-01-2014, 03:06 PM
I definitely ordered potassium carbonate from Fast Chem via eBay. I've since read that K2CO3 makes wine musts darken a bit but subsequent fermentation will take care of it. In regards to the smell, having thought about it it was less a smell and more a kind of 'harsh' feeling in my nose... CO2 perhaps?

What temp are you at? You may need to get it a bit warmer to activate.

And yes, it sounds to me like the smell you got was a bit of CO2 from degassing. Just because your airlock doesn't move or you notice no foam does not mean the yeast aren't fermenting. Check your hydrometer, report back.

03-01-2014, 06:12 PM
The ambient temperature is about 20c, must is a little cooler at 18c. The smell eventually dissipated so I added it to the must and it fizzed up, but didn't do anything noticeably untoward. Fermentation is definitely occurring but hasn't dropped a point in the last 48 hours (still at 1.04) so I'm repitching as per bernardsmith's post. I will report back.

On a side note, I'm now using GV10 (Gervin) which is meant to be good for restarting. This stuff goes off like a volcano, even in an open container!

03-10-2014, 01:42 PM
So, repitching has worked (after two attempts) and the SG is now dropping (1 point in the past 24 hours). However, I've noticed that the must has developed a very bitter taste. I'd describe it as a 'quick' bitterness in that it doesn't last long and it then has a residual saltiness to it. Is this the taste of potassium carbonate? Is the bitterness likely to precipitate out?

03-10-2014, 11:48 PM
The carbonates and bicarbonates (potassium and sodium) can impart a slightly metallic "salty" taste, but that won't last since your yeast will consume most of the available potassium as a nutrient during the rest of primary fermentation. Likewise the bitterness is probably more of a taste of the new yeast and it should go when the spent yeast precipitates out.