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Doing my 2nd batch (after a break of 20 years :) ). Its a LME / DME porter attempt. It all went according to plan and the OG = 1045. It started fermenting more or less on time, but was sluggish from the start. From what I can see, it only built up a krausen of max 1cm. It was blubbing nicely for a few days but has slowed down now at 72 hours. Just took a sample (have a tap on the fermentation vat, so no disadvantage to doing so) and it's still at 1030. I haven't found any info or rules of thumb indicating where it should be. The yeast was a M42 New World Strong Ale Yeast. Should I repitch, or will I hit 1010 - 1015 with a few weeks of fermentation + bottle conditioning?

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    what temperature is the brew at? did you follow the package instructions regarding rehydration? what was the date on the yeast? But I think you may be simply over-concerned. I would just leave it, and raise the temp to 20C if it's not already there.
    – mdma
    Jan 6, 2017 at 9:47
  • Thanks for the answer. The room is at 20C. The yeast had only instructions to "Sprinkle directly on up to 23 L (6 US Gal) of wort." which I didn't do. I kind of followed the instructions from Palmers How To Brew. I used a sterilised jam jar with the correct temp water with the lid on. I also gave it a gentle shake instead of stirring. Are yeast sensitive like that?
    – dashambles
    Jan 6, 2017 at 9:55
  • 20°C is good, your yeast works best between 16 and 22, so temperature isn't the issue. You can retake a gravity sample after 2 more days to confirm if it is still active or not.
    – Philippe
    Jan 6, 2017 at 16:48
  • Ok I'll resample on monday. It still is releasing a bubble every 30s or so even today after a full 5 days.
    – dashambles
    Jan 7, 2017 at 19:46

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Firstly, welcome back to the world of home brewing.

Dried yeast during re-hydration are sensitive, but a little gentle shaking will not ruin the viability.

I would leave it for about 7 days from pitching if you are no where near FG by then, then make a small starter and pitch that. Once there is alcohol in the mix you really want to make a starter to ensure your dried yeast are most importantly re-hydrated when re-pitching. As if they are not the alcohol can diffuse quickly through the dehydrated cell walls and damage the cells. This is less critical with liquid yeasts.

There are a few things that may be affecting the fermentation:

  • is the wort sufficiently aerated?
  • was the yeast nice, fresh and well stored?

My guess would be either the yeast had been poorly stored (got too hot) before you purchased it or the wort was not sufficiently aerated.

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  • Thanks for the answer and the links, still reading through them now. Could be the aeration as you say, but similar aeration worked the last time. But the boil was longer this time. Do you have any info about approximately how the gravity varies over time and how much I could hope to drop in the bottle?
    – dashambles
    Jan 7, 2017 at 19:56
  • You want to ensure you have fermented out before you bottle and prime back or you can end up making bottle bombs; never fun! I will try dig out some stuff on fermentation curves, if I forget ping me again.
    – Mr_road ♦
    Jan 8, 2017 at 23:37
  • I did it now so as not to forget, take a look at images for this google search: google.co.uk/search?q=fermentation+curves
    – Mr_road ♦
    Jan 8, 2017 at 23:40
  • OK so I did a resample just now which is exactly 1 week after pitching and it is down to around 1025. It is still bubbling away somewhat at around one bubble every 30s, which seems the same as at 5 days. I found the note with the OG on it and it was 1048 and not 1045 as stated above. So 1048 at 0, 1030 at 5 days, 1025 at 7. Gut feeling says it will go down to around 1020 after another week? What do you think, from what I have read 1020 would be borderline ok?
    – dashambles
    Jan 9, 2017 at 16:07
  • I would not bottle at 1020. I would wait till you take 3 days readings with no change then prime back when bottling. 1020 is way too much residual sugar depending on the yeast it should finish 1006-1012 range, but check you have those 3 the same to show it has fermented out.
    – Mr_road ♦
    Jan 9, 2017 at 19:00

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