Stuck Fermentation

[IRBrew]

My American Stout has stuck at 1.018. It's been there for five days now (day 12 of fermentation). I stirred it and upped the temp a bit on day 7 but it hasn't moved since. My OG was 1.061 and my target GF is 1,015. I'm thinking of adding a yeast starter to try and finish it off. It's a 12L batch. I have DME and dried yeast. What quantity of starter and yeast should I aim to make up? Or should I up the temp a bit more, give it a few more days and settle for that?

 

[Zephyr259]

You're at 71% apparent attenuation so you could be done.

What was the grain bill, mash temp and yeast used? Then we can advice more accurately.

Thanks

 

[IRBrew]

Here's the grain bill for 12L:
Pale Malt (2 Row) UK Grain 2.500 kg
Brown Sugar, Dark Sugar 300.000 g
Oats, Flaked Grain 200.000 g
Simpsons - Black Malt Grain 180.000 g
Simpsons - Roasted Barley Grain 55.000 g
Weyermann - Dehusked Carafa II Grain 50.000 g
Mash temp was 66-67C
Yeast S-04

Cheers, Ian

 

[Zephyr259]

Yeah, I'm getting the same figures as you, should finish closer to 1.015, and if the sugar fully ferments as it should then could go down to 1.013 fg. I'm a bit more cautious now as my most recent bottled beer seems to have attenuated an extra 0.002 after bottling and along with the priming sugar the beer foams like crazy and gushes a bit on opening if I'm not quick, so it pays to be patient. That beer had been sitting for 4 weeks though...

I've not had to deal with a stuck beer before but one of the issues is that to get it going with fresh yeast you need to pitch a huge amount as it's not going to be growing any, think that was discussed on Experimental Brewing. Adding an active starter might help but I've no experience doing so.

You're only at day 12 so it could still be fermenting away slowly, maybe another rouse is worth it?

I'm sure others with more experience will be along to offer their advice, but they now have all the facts.

Good luck.

 

[Sandimas]

Yeast S-04

That could be your answer.

I recently posted a similar question, because a Porter had finished high. A few people suggested S-04 tends to do that with dark beers, I didn some more searching on the web and it seems to corroborate that. And when I looked back at my brewing records most of my dark beers with S-04 had finished high.

I now tend to use Gervin/Nottingham yeast with my dark beers.

 

[hoppyscotty]

Is it just dark beers you've had issues with S-04 with? I've just done 2 Pale Ale brews with it and despite hitting all my numbers going into the fermenter I'm way off my FG. Still investigating temp control of my fermentation cabinet/fridge but if I don't find an issue with that I'm a bit lost as to what I've done wrong.

 

[foxy]

My American Stout has stuck at 1.018. It's been there for five days now (day 12 of fermentation). I stirred it and upped the temp a bit on day 7 but it hasn't moved since. My OG was 1.061 and my target GF is 1,015. I'm thinking of adding a yeast starter to try and finish it off. It's a 12L batch. I have DME and dried yeast. What quantity of starter and yeast should I aim to make up? Or should I up the temp a bit more, give it a few more days and settle for that?

If your gravity is due to none fermentables which I would say it is then adding more yeast would be a waste.

From How To Brew - Palmer
Dark caramel and roasted malts like Crystal 80, Crystal 120, Special B, Chocolate Malt, and Roast Barley have a high proportion of unfermentable sugars due to the high degree of caramelization (or charring). The total soluble extract (percent by weight) of these malts is close to that of base malt, but just because it's soluble does not mean it is fermentable. These sugars are only partially fermentable and contribute both a residual sweetness and higher FG to the finished beer. These types of sugars do not share dextrin's digestive problems and the added flavor and color make for a more interesting beer. The contribution of unfermentable sugars from enzymatic and caramel malts can be increased by mashing at a higher temperature (i.e. 158°F) where the beta amylase enzyme is deactivated. Without this enzyme, the alpha amylase can only produce large sugars (including dextrins) from the starches and the wort is not as fermentable. The result is a higher final gravity and more body.

Is it just dark beers you've had issues with S-04 with? I've just done 2 Pale Ale brews with it and despite hitting all my numbers going into the fermenter I'm way off my FG. Still investigating temp control of my fermentation cabinet/fridge but if I don't find an issue with that I'm a bit lost as to what I've done wrong.

Make sure your targeted mash temperature is in the ball park, to high and your FG will not be achievable, to low and you can overshoot and end up with a thin beer.

 

[IRBrew]

Thank you for the helpful replies. I'm a huge fan of dark beers and I've done three others. A foreign extra stout which finished high 1.020 against 1.015), a dry stout which finished high (1.014 against 1.008) and and a porter which finished low! However apart from the porter there is a pattern here as none of my other beers fail to reach FG. Now I must say that the FES is one of the nicest beers I've ever tasted and I'm sure that the extra body is due to the unfermented sugars, so it's not necessarily a bad thing with this style of beer, I just don't want exploding bottles! So I'm not going to worry about my current brew. I'll give it a couple more days and then bottle.

 

[Sandimas]

You should be fine bottling, my Porter was 1018 and is lovely and not over-carbonated, bottled in Sept.

 

[hoppyscotty]

Should a nicely fermenting wort be slightly warmer than the surrounding temperature? I'm assuming that if fermentation warms up the wort a bit and the probe is on the side of the FV then the inside of the fermentation fridge should be a bit cooler? I've had a few issues with fermentation over my last couple of brews (actually my first brews) where I've fallen around 10 points short of my FG after 2 weeks - 1026 from 1046 OG and a target of 1011. Decided to monitor this third one a bit more closely and its at 1033 from 1046 after 1 week and doesn't look like it's particularly active even after turning up the temp a degree. I've measured the temp of the inside of my fermentation fridge as the probe is stuck to the side of the vessel and the two temperatures are the same. Should I see a difference? I.e. should a nicely fermenting wort be a bit warmer than its surroundings?

 

[Zephyr259]

Should a nicely fermenting wort be slightly warmer than the surrounding temperature? I'm assuming that if fermentation warms up the wort a bit and the probe is on the side of the FV then the inside of the fermentation fridge should be a bit cooler? I've had a few issues with fermentation over my last couple of brews (actually my first brews) where I've fallen around 10 points short of my FG after 2 weeks - 1026 from 1046 OG and a target of 1011. Decided to monitor this third one a bit more closely and its at 1033 from 1046 after 1 week and doesn't look like it's particularly active even after turning up the temp a degree. I've measured the temp of the inside of my fermentation fridge as the probe is stuck to the side of the vessel and the two temperatures are the same. Should I see a difference? I.e. should a nicely fermenting wort be a bit warmer than its surroundings?

Sticking a probe to the side of a fermenter is thought to be reasonably accurate, but you do need to insulate it from the surrounding air. I fold up a cloth and tape it over the probe, I've seen others use plumber's putty or bubble wrap. If it's just stuck to the FV then it's going to be measuring the air more than the beer.

On your FGs, your not using a refractometer are you? The alcohol present throws off their reading once fermentation begins.

 

[hoppyscotty]

Thanks Zephry. I've used a floating hydrometer too. Have insulated the probe from the outside and have been investigating the fermentation fridge just to make sure it's not doing anything odd, so put a thermometer in there too and it measured the same temp as the probe on the side of the fermentation vessel. Not sure if that is to be expected or not. I'm thinking that if the fermenting wort produces heat then the probe will hit target temp before a thermometer in the fridge and cut off any heating so the fridge temp might be a bit lower than the wort temp...I'm guessing really just not sure if this assumption is correct. Will check the gravity in a day or so and the temp and if still not moving anywhere then will pitch some more yeast.

 

[foxy]

Fermentation creates exothermic action, the core of the wort will be 1-2 C higher, lower temperatures do not stop yeast working, just slows them down. Some home brewers do mash at lower temperatures purposely, saying they get a better beer.
Its better to get a grip on the enzymatic behaviour of the mash and start from there, even doughing in can have an effect on a final gravity.

From BYO


Final Gravity
Final gravity measures the attenuation of the beer, which is the reduction of the wort’s density caused by the fermentation of sugars into alcohol and carbon dioxide. Fermentation also leaves behind dextrins (non-fermentable sugars), proteins, and peptides, all of which combine to form the density of final gravity readings. These dextrins, proteins, and peptides also provide body and mouthfeel.

Final gravity readings help define each beer because the density of the finished brew determines alcohol content and overall balance. An American pale ale with an original gravity of 1.054 but a final gravity of 1.020 missed the mark because the final density of the beer will provide too much body, which then masks the hop bitterness, leaving a beer malty rich and out of balance for the style.

Brewers should always examine all possible causes of high final-gravity readings, such as improper aeration of the wort, low fermentation temperature, lack of viable yeast, or too many dextrins. Low final-gravity readings can be caused by wild yeast contamination, bacterial contamination, or not enough dextrins. A careful examination of sanitation, brewing procedures, and yeast source can solve many final-gravity problems.

Extract brewers may also find that the extract source contained too few dextrins for a high final gravity or too many dextrins for a low final gravity. As when fine-tuning original gravity, combining extract syrup with dry extract may solve this problem as well. For extract brewers adjusting the amount of available dextrins is the only way to adjust final gravity and mouthfeel in a successful brew, because malt extract does not include the proteins and peptides generated by all-grain mashing. Only experimentation and strict notation will help extract brewers obtain target final gravities.

All-grain brewers should examine the mash schedule. Well-modified malt mashed in with a single-step infusion method should stabilize within a range of 150 to 158 °F (66 to 70 °C). A mash held at 150 °F (60 °C) will produce mostly fermentable sugars, generating a delicate brew with light body and mouthfeel. A mash held at 158 °F (70 °C) will produce a blend of fermentable and non-fermentable sugars, creating a brew with either medium or full body.

For example a Continental style stout with a 1.055 OG finished at 1.008 FG. Batch notes state that the mash temperature stabilized at 158 °F (70 °C) for an hour but actually started at 148 °F (64 °C), requiring 20 minutes of forced heat to raise the temperature. Well-modified malt held for 15 minutes within the 150 to 158 °F (66 to 70 °C) range will reach total saccharification, with all starches converted into sugars. The stout seemed thin for style. In the short time that heat was applied to raise the temperature, the starch converted primarily to fermentable sugars, well before reaching the higher range of temperature required to produce dextrins. Batch notes then suggest that the strike temperature of the water added to the mash to reach conversion temperatures should be raised so that the mash will immediately reach 158 °F (70 °C) before conversion.

Another solution includes the addition of cara-malts, including cara-pils, cara-Vienne and cara-Munich, into the total grist bill. These specialty grains are designed to produce dextrins. Eight ounces of any of the above cara-malt will raise the final gravity of a 5-gallon (19-L) brew.

All-grain brewers enjoy the ability to lightly raise or lower mash temperatures while adding or decreasing, if necessary, dextrin malts to produce a perfect blend of fermentable sugars, dextrins, proteins, and peptides. Only experimentation and strict notation will help all-grain brewers obtain target final gravities in each batch.