Baffled by H2S production

[BWRIGHT]

Started (2) 1 gallon(ish) meads a couple of days ago. Came home today and was puzzled/concerned that my dining room smelled like H2S. Thought I had everything worked out pretty well but seems I have a hole in my process. Anybody want to point it out for me?

Batch 1

1 gallon spring water
4 lbs pineapple
3.5 lbs honey (Bocheted)
71 b yeast (re hydrated with GoFerm per directions)
Fermaid O (5.6g total. 4 additions at 24, 48, 72, 1/3 break)
Pectic Enzyme

Bocheted the honey for approx 30 mins, let cool a bit, added the spring water to the honey, stirred, added to bucket. Added pineapple. Crushed 1.5 Campden tabs, added them, stirred well. Let sit for 24 hours. Next day I added the pectic enzyme (1.5 tsp), and the 71 b which was rehydrated with GoFerm (6.25g). Stirred well with drill and lees stirrer. Next day (24 hours post pitch), I degassed with the drill and added the first dose of Fermaid O. Come home today (48 hours post pitch) and my dining room has the undeniable H2S smell. I degassed again and added a bit more nutrient than the recipe called for to try and counter. Temp was 70F. No airlock on the bucket, just a sanitized paper towel.

Batch 2

Identical other than I used a mixed berry blend rather than pineapple and did not bochet the honey. Went to take a PH reading but my battery was dead. That is the only culprit I can think of that would stress the yeast but as forgiving as 71b is, and the fact that I've not encountered H2S with 71b prior, I am baffled. Thinking maybe I should adjust the TONSA recommendation from 24, 48, 72, 1/3 break to.......0, 24, 48, 1/3 break? With all that fruit in there, I figured I should probably adjust the total nutrient down but even having too much nutrient, not sure how that would stress the yeast?

 

[bernardsmith]

Yeast asked to ferment sugar in the absence of sufficient O2 can belch out H2S as their ironic thanks, and some yeasts routinely are large producers of hydrogen sulfide even when swimming in oxygen, though I have never had that problem with 71B, but depending on the way that they are grown and stored some fruit is bathed in sulfurous products (waste water irrigation; pesticides etc and so the raw materials for the production of H2S are easily accessible.

One thing you can do is increase the amount of O2 in the wine. Whip air into the wine and that can both blow off the H2S and help the yeast get rid of what remains. If that fails you can try racking the wine while allowing it to splash against the wall of the target carboy AND rack through some copper scrubbing wool. The copper will bind with the sulfur.
The larger problem is that H2S if allowed to remain unchecked can further metabolize into mercaptans... and if H2S is a pain to remove mercaptans are all but irremovable... and they really do spoil the wine.

 

[BWRIGHT]

Right. I'm with you on all of that. I've experience some H2S production early on in my brewing adventures before I understood a little more about yeast. Had the sulfur smell on some early ciders but haven't seen it since and definitely not with 71b. I guess maybe I didn't get enough oxygen into the must pre pitch?

Either way, after I degassed quite a bit, added the second dose of nutrient, and waited 24 hours....it is gone. They seem to be satisfied now. Just wish I knew how I stressed them at all.

 

[bernardsmith]

I suspect that a lack of sufficient O2 during active fermentation is a major cause of H2S production. Yeast NEED oxygen for a clean fermentation. And they will use up any O2 you provide before you pitch the yeast in moments.. not hours.. moments. This is one reason that many wine makers ferment fruit in open buckets loosely covered with cloth and not in glass carboys sealed with a bung and airlock. Before you press the wine out of the fruit and rack to a secondary you want to give the yeast access to O2. A week or two or more , if the yeast are active they will grab that oxygen before it can oxidize the fruit. After active fermentation has ended that is another story and then O2 is not your friend.

 

[BWRIGHT]

Appreciate the feedback Bernard. I did fail to mention that I did not have an airlock on either of these buckets for the first 72 hours. That is my standard practice. I just put the lid on without snapping it and cover the grommet/hole with a wet, sanitized rag. So knowing that, do you suspect it was still a lack of O2 that kicked off the H2S production? I didn't hit it with pure O2 at any point. Just stirred well with a drill and lees stirrer. I make a point, after I know the honey has been dissolved, to focus the stirrer on the top of the must to try and maximize whatever air I can get into solution. Always seemed to serve me well, which is why i was puzzled by this. I'm not really concerned about fusels or off flavors as I think it was corrected within 24 hours. I'd just like to clean up/improve my process wherever possible. I made a lot of swill mead when I was more ignorant about the dark art of zymurgy; hoping to keep those days in my past by constantly improving my methods.

 

[bernardsmith]

I certainly do not have the chemical knowledge to comment further but I think H2S tends to occur in oxygen poor environments. When the environment is oxygen rich the hydrogen does not bind with the sulfur

 

[Maylar]

From what I've read, the need for oxygen exists only at the stage before active fermentation starts - typically about 24 hrs after pitch. With mead, we generally whip the must up pretty well just by mixing in the honey, so O2 is present by default. In my own process I like to oxygenate the must with an O2 tank and wand, at pitch and at 24 hrs, no later. But lack of O2 isn't a primary cause of H2S, it's lack of nutrients (nitrogen) that does that.

Yeast need nitrogen and if it's not there they will break down some amino acids and extract nitrogen from them. A byproduct of that process is H2S. In my own experience, the only time I've had rhino farts is when I didn't add enough DAP at the start of a cider batch.

 

[bernardsmith]

I agree that a lack of nutrients is also a possible problem but the OP had added more than 5 g of Fermaid O.
Adding O2 before pitching the yeast even if you pump in O2 from a cylinder is not likely to provide anything like sufficient oxygen. (see Yeast by White and Zainasheff, pps 79-84)