From a mead/honey must/grape wine/fruit wine perspective, adding more yeast is no longer a best practice protocol. Dr. Linda Bisson (PhD UC Davis, who taught my Wine Stabilization and Aging class) has some very cool research on this subject.bwarbiany wrote:This is a good time to ask this question... For a stuck ferment, is there any advantage to pitching more yeast? I always figured that since the yeast have likely multiplied FAR in excess of the number of viable cells in a pack of dry, you're not really going to get any advantage... Is this accurate?
There is active research on this subject that is gaining momentum in the wine chemistry world that a stuck fermentation is due to a number of compounds that inhibit the yeast from maintaining a sustained, healthy and vigorous fermentation. Adding more yeast in this case will not suffice to stimulate a stronger ferment, and will actually add additional unfavorable inhibitive compounds into the medium being fermented.
Current favored protocol for stuck wine/mead/cider fermentations is to do the following.
Check your current brix/SG
Add 1 gram of yeast hulls per gallon of stuck must to the stuck must, stir and let settle.
Rack off the lees into another clean, sanitized vessel.
Prepare a one gallon RE-starter must (grape, honey or fruit, whatever your fermentation is made from) with an SG of 1.050
Rehydrate a yeast known for re-start capabilities (EC-1118, QA23, K1-V1116 or UVAFERM 43) as per manufacturer's spec (5 grams of yeast in a one gallon must is sufficient).
Inoculate the RE-starter must with the yeast and add 1 gram of Fermaid K per gram of yeast used in the Re-starter must at the end of the lag phase and aerate liberally.
Add 2 grams Fermaid-K per gallon of the stuck must into the stuck must.
Add 1/2 gallon of the stuck must into the RE-start must and allow it to get to vigorous fermentation.
Repeat adding 1/2 gallon to the RE-start must until the entire stuck batch has been added in and is vigorously fermenting, this may take a while but it is better than pitching some very costly grape or honey must.
Aerate twice daily and monitor the fermentation progress.
OK, the reason for all of this is as follows:
The yeast hulls will serve a number of purposes. One is to adsorb toxic/inhibitive compounds in the must and then settle to the bottom of the fermentation vessel making it easier to leave those toxins behind when you rack. Secondly they will provide nitrogen and increase YANC (Yeast Assimilable Nitrogen Content) in the must and provide amino-based nitrogen. At this point in the fermentation adding Sodium based nitrogen (DAP and other early fermentation nutrients with ammonium phosphate and Urea are not desirable and will have a negative effect on the fermentation when trying to restart). Lastly they will provide sterols and chitin for the newly pitched RE-start yeast to help the new generation of yeast with their uptake of oxygen, squalene and ergosterol which will build a strong, elastic and alcohol resistant cell wall which will in turn help to regulate cellular pH, metabolism, nutrient uptake, respiration and osmotic pressure regulation which all work together to ensure a happy healthy yeast population. Happy, healthy, strong and hungry yeast mean a fast, clean and complete fermentation.
Hope that helps,
Oskaar
, I'm sure it's non factor.
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