Organic nutrients and restarting fermentation

[Thomas Christie]

Hi all,

This is my first time posting to the group, I’ve been following discussions here for a little bit and you all make for such an invaluable cider making resource. 

I’m looking for some advice on restarting a stalled fermentation in a cider I aim to bottle with some residual sugar. 

This batch was pressed on 10/17 and spontaneously fermented with an initial gravity of 1.07. After a couple of rackings and a couple of months, the gravity was down to 1.030 and progressing at about 100 FSU at an ambient temp of 55f. In a desperate effort to slow the fermentation, I added a small dose of kieselsol and chitosan before cold crashing and racking. This apparently worked better than I expected, the cider was as a result quite clear but also seemed to have stalled. After a couple weeks of no airlock activity and no measurable change in gravity while being kept in my apartment at 65f I decided to try adding some nutrients to restart fermentation.

I tried to follow Claude’s recommendation from his book of a 25ppm DAP addition for a 10 point drop in gravity, however I only have organic nutrients (FermaidO) and so tried a dosage that would make for an addition of 5 “YAN equivilants”, as organic nutrients are supposedly 3-4 times more efficient than inorganic nitrogen. Within a few days there was renewed airlock activity, but within a week this activity had stopped, with an apparent drop of ~1 or 2 points of gravity (I’m waiting on my precision hydrometer so measurement is difficult). In roughly a week since then there’s been no measurable change in gravity. 

Does anyone have experience using controlled doses of organic nutrients like this? Should I just get some DAP and follow Claude’s dosage? I’d really like to be able to bottle this pet nat for an incomplete fermentation in bottle and resulting residual sugar. Thank’s for any advice! 

-Tom Christie 

[Claude Jolicoeur]

Be patient... After a nutrient addition, it takes at least a month to really see that something is happening. A precision hydrometer will help. 

However, no I don't believe that organic nutrients would be 3-4 times more efficient by weight. Where did you get that information from?

As far as I know, most organic nutrients are from dead yeast cells that contain about 10% Nitrogen by weight, while DAP contains about 20% Nitrogen - thus making DAP twice more efficient than the organic stuff at equal weight... But this is theoretical, and would need to be tested.

[Thomas Christie]

Hi Claude,

I suspected patience may be the answer here… 

3-4 times more efficient is the claim from the manufacturer, and the idea is more efficient by nitrogen content rather than by weight. For this reason they suggest dosages according to “YAN equivalents”. So for example if you wanted a dosage of nutrients equivalent to 100ppm YAN as provided by DAP, they suggest a FermaidO dosage that actually contains only 33ppm measurable YAN. 

The claim is that nitrogen provided by amino acids is more efficient for fulfilling cell metabolic needs than that provided by ammonia, the analogy I’ve seen is that inorganic nitrogen is like “candy”, yeast assimilate it quickly and sprint through some fermentation for awhile before crashing and needing further additions to continue fermenting. Meanwhile organic nitrogen is the “balanced diet”, leading to slower and steadier fermentation. 

It’s just occurred to me that there may also be an issue here of assimilation in the presence of ethanol, I think it might be that organic nitrogen uptake is inhibited at higher levels and that could also be a problem for me. So perhaps I’ll give it a month to watch for any change and meanwhile get myself some DAP to dose according to your suggestions. 

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[Mark Fitzsimmons]

Thomas,

Scottlabs has a great article on restarting stuck fermentations here: https://scottlab.com/restart but be aware that some causes of stuck fermentation can be bacteria that inhibit yeast reproduction and these can also produce "off" flavors, and for this reason, restarting with a big yeast starter is recommended to be done asap, or said bacteria can continue to do more damage to your beverage. The protocol in this article is based on getting a very large healthy yeast colony going. It also has some steps at the beginning to remove some of the contaminants which may be causing the stuckness. Since you already clarified with kieselsol and chitosan, I would skip the first couple steps and rack off your lees before adding the new healthy colony to take out whatever those adverse compound inhibiting the new yeast which are present.

Also be aware that above 10% abv, yeast is completely unable to "eat" nutrients, because it's unable to pull them across the cell wall. I believe i read somewhere that this inhibition actually starts happening around 8%ABV, and then becomes absolute north of 10%, so most yeast additions are normally recommended to happen below 4-5% ABV, and you load them up with enough food to get to the finish line (especially true for very high alcohol finishing above 15%). You are getting pretty close to this 8% threshold, so the big yeast colony which is "preloaded" with plenty of nutrients as per the protocol linked is a safer way to avoid "vitamin" flavors in the final beverage.

[Thomas Christie]

Hi Mark,

Thanks for the link. I am familiar with stuck fermentation protocols, and might resort to that if I don’t have success with the strategy of small nutrient additions. I haven’t gone that route thus far because I’d really like to be able to bottle this batch such that it finishes with some residual sugar. So far there are no signs of off flavor or aroma, but I’ll be keeping a close eye on that and intervene if necessary.

-Tom

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