Stuck Ferments


If your fermentation peters out early in the story, it could be due to a couple of reasons.
  • Nutrients. This will be the biggie. These are necessary if just using sugar/water. If this is why its become "stuck", then there will be little chance of reviving it (sorry). See the discussion Nutrients for more details.
  • I sometimes suspect that I haven't diligently rinsed all the bleach from my fermenter, and that this has killed the yeast. Repitching with more yeast gets it going again (and remember to rinse better next time).
  • Sometimes you haven't added enough yeast (there almost is no such thing as "too much" yeast). Use a couple of packets if you are using those little 5-7g sachets.
  • Temperature problems - too hot will kill the yeast, to cold will make it dormant. Keep the temperature between 26-34 °C, and keep it constant - varying the temperature will jepardise its run.
Do not add more sugar to a stuck ferment. It won't help.

You can still distill a wash which hasn't fully fermented out, but be prepared for some fun. It is likely to foam up heaps, and possibly block the column if you don't give it enough headspace, or use the "anti-foaming" silicon emulsions (wash conditioner) available in brewshops. Also, because not all the sugar has fermented, you're likely to get less alcohol out, and you may caramelise a bit of it on the element or the base of the pot (clean it well afterwards).


Heres a couple of emails between Steve & Dr Clayton Cone that are hugely informative ..
    Below is the reply to my enquiry re turbo yeasts and stuck ferments. Dr. Clayton Cone is a microbiologist and consultant at Lallemand which is the manufacturer of the Lallevin EC1118 yeast which is good for up to 18% alc/vol. He provides a protocol for the production of high alc wines/washes below. You may wish to put the following links on your site, www.lallemand.com and www.redstaryeast.com The latter has an interesting text on the history of yeasts.

    Regards, Steve


    Steve,
    I hope that you had a chance to read my articles in the Lalvin Home Wine Making section of the Lallemand.com. I try to cover the role of yeast rehydration, nutrients, oxygen, stirring, pH and other factors that are involved in a healthy fermentation that should assure you of a complete fermentation.

    Most stuck fermentations today are caused by:
    1. Mishandling at rehydration. Follow instructions very carefully.
    2. Allow the temperature to rise too high.
    3. No oxygen (aeration) during the first 36 - 48 hours.
    4. No stirring or agitation during the first days of the fermentation and near the end. The yeast settle out and are not up in the must where all the sugar is.
    5. Lack of yeast nutrients.
    6. Too low pH
    7. Toxic effect of Octanoic and decanoic fatty acids

    I would first try to reactivate the yeast by adding Vi A Dry yeast residue and stirring, allowing a little air to get into the must. Stir several times for several days. If no activity is observed then you need to do one of the following:

    1. There will be no yeast growth with all of the alcohol present so you must add a large number of live yeast to finish the job. Add 10lbs of properly rehydrated EC 1118, K1 or L2226 directly to the stuck wine and aerate and stir.
      or
    2. Calculate the right amount of EC 1118, K1 or L2226 required for the total volume of stuck wine at 5lbs/1000 gallons. Rehydrate the yeast in 10 time its weight in 105F tap water. Add the dry yeast slowly to the water while stirring to avoid lumping and allow to stand for a maximum of 30 minutes.

      Add the rehydrated yeast to the following initial mixture which is 5% of the total stuck wine volume:
      • 2.5% of volume of stuck wine (25 gallons/1000 gallons)
      • 2.5 % of volume as water (25 gals./1000 gal.)
      • 2.0 lbs. Fermaid K & 2 lbs DAP /1000 gals. Of wine/water mix
      Adjust sugar level of this mixture to 5% with juice concentrate or sugar (40 lbs sugar/100 gals)

      Maintain temperature at 70 - 75F

      When the sugar level has dropped by 1/2 (<2.5%), begin to add the stuck wine to this starter. Add 2lbs Vi A Dry yeast residue/1000 gallons of stuck wine before starting to add to the starter*. Add in batches of 20% of stuck wine volume. When the sugar has again reduced half add the next batch. Continue untill the fermentation has completed.

      * This will adsorb the octonic and decanoic fatty acids that might be present and also furnish nutrients for the yeast.


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