A very stinky cap set.
Previously, I wrote a little about YAN levels and their relevance to successful, clean ferments. I left that subject uncertain how nutrient additions should be adjusted based on the YAN level.
It was later in the week that I spoke to John Daume, owner of the The Home Wine, Beer and Cheesemaking Shop in Woodland Hills. He pointed me to the Yeast Nutrient Addition Chart available on his web site (also, here – please note that teaspoon to gram and ounce conversion at the bottom of the first page is my addition; blue – from my phone conversation with John; in red from my calculations after weighing half a teaspoon of SuperFood Plus).
In my previous post, I also asked how one would deal with low YAN as the proportion of low amino acid nitrogen to low ammonia nitrogen varied. John said that one acts on and “treats” the whole YAN value. Nevertheless, I think it’s reasonable to say that if one’s ammonia nitrogen value is disproportionately low, one can ad more DAP (although it should be pointed out that the majority of products like Fermaid K or SuperFood plus is, in fact, DAP).
Yeast Risk Factors. From: Beverage Supply Group catalog. bsgwine.com
Assuming that 10 gallons of must will give me seven gallons of finished wine, I added 1.5 teaspoon of SuperFood Plus before inoculation. I then added another teaspoon as the ferment got stinky. Finally, I added 1.25 teaspoons as the wine reached 15°Bx. This last addition roughly corresponds to the Stage 3 addition for moderate-to-high risk grapes.
Now, the risk factors in the chart above are fairly vague and only help alert the winemaker to potential issues. If you want to know exactly what you’re dealing with and whether you’ll be able to make a non-interventionist wine, check your YAN.
It’s not that expensive:
Places like Baker Wine & Grape Analysis in Paso Robles, can turn around the test in a few hours. This particular lab needs a minimum 50mL sample (drawn at crush, before anything is added to the must), topped and sealed tightly, sent overnight packed with an icepack and a check for $30 ($40 if you want them to break down the YAN to ammonia and aminos). They can send the results by email, if requested.
The alternative is, if you live in or near wine country, to see if a larger winery with its own analyzer (spectrometer) can run this test for you.
The reason I’m spending all this time on this subject (both researching and writing about it), is that I’ve been hit with one of the possible consequences of vinifying low-YAN grapes: a ferociously stinky ferment. The basement smelled as if a sewer pipe had ruptured in there. The stench was so bad, that there was no perky, grapey aromas of a clean Montepulciano ferment.
I’m glad to report that through a combination of temperature control, frequent splashy punch-downs (every two to three hours, while I’m awake) and addition of SuperFood Plus, the smell is dissipating and clean fruit aromas are starting to come through. Hopefully, my frequency of punch-downs strikes the right balance between enough to get the stink out and get oxygen to the yeasts but not so much that it blows off desirable aromatics.
There is no guarantee that I’ll get the wine completely cleaned up before it finishes. In which case, I’ll have to go with the weapon of last resort:
Mercaptan kit.
ADDENDUM:
These are two good pieces about yeast H2S production during fermetation:
“Eliminating formation of hydrogen sulfide by Saccharomyces” – http://www.practicalwinery.com (back-up copy)
“Regulation of Hydrogen Sulfide Liberation in Wine-Producing Saccahromyces cerevisiae Strains by Assimilable Nitrogen” – Applied and Environmental Microbiology (back-up copy)
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