H2S After Blending

[Patrick McCauley]

Hi All. I'm wild fermenting all of my ciders, and also use racking and clarification to get very slow and incomplete fermentations on most of my batches. Every once in a while, I will get hydrogen sulfide taint in my ciders, but despite all of interventions to starve the yeasts of nutrients, it's rarer than you would think. Maybe once a year for the 15 or more batches I do. Late last summer, I pressed some Otterson apples, which were much earlier than the rest of my cider apples. I fermented them to dryness, and then blended them with later, high sugar and lower acid apples. This is when the H2S taint developed. I treated it with copper sulfate, which seemed to work, but it has reemerged in the bottle. This is not the first time this has happened, where the H2S taint happened after I blended an early cider with, and still-fermenting late-season cider. Just curious if anybody has had this issue? I'm wondering if blending the late-season cider that is still fermenting with a finished and nutrient depleted cider is stressing out the yeasts in the still-fermenting cider? Any tips would be appreciated. Thanks!

Pat McCauley 

[Alexandra Beaulieu Boivin]

Hi Pat,
Two things jump out that can explain why H₂S seemed fixed with copper and then reappeared after blending/bottling:

1) Blending a still‑fermenting cider with a finished, nutrient‑depleted one can re‑stress yeast. I usually recommend not adding additional sugar to fermenting yeasts past the 1/3 fermentation completion. 
Restart with a healthy build‑up (levain) rather than relying on a stressed population. Aeration during active fermentation is protective and can fully remove volatile H₂S when monitored properly. Identify it early by tasting and smelling daily and make sure that it is fully removed. When picked up early oxygen will work wonder. Also oxygenating during fermentation can be more safely done than afterwards. 

2) Post‑bottling sulfur chemistry can “re‑liberate” smelly molecules over time.
It is common in bottle conditioned product pre-treated with copper sulfate for H2S. I have seen it a bunch. Again, taste and smell daily, catch H2S early and treat with oxygen. Once it evolved into mercaptans and disulfide, that's when you use copper and there are risks it will come back. Clarifying after copper treatment will help. 

It is also possible that the cider was low in YAN at bottling. 

Alexandra

@alexandravinumartisan