H2S Smell followed by loss of color in Cab and Syrah

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Aug 30, 2017
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I made two wines last Fall from some CA Cabernet and Syrah grapes. I added some DAP and Fermaid to both musts at the outset, and again about 3 days into the fermentation. I kept the buckets in my cellar which was about 55F at the time. The fermentations of both wines were extremely robust, to the point of spilling over the buckets despite have broken each wine out into two buckets to leave room for foaming. About 5 days in, I started to smell H2S even though I was punching down the cap 3 times a day. I have been doing hard splashes when I rack the wine to try to blow off the H2S, but, I have also noticed that the color of these supposedly deep red wine is a very light red. On the last racking, I noticed what looked like red acid crystals formed on the sides and especially at the bottom of the carboy. It is as though all the color fell out of the wine, and that the acid levels were high enough to fall out of solution in my cool cellar. The wine still smells a little sulfury, and has a slightly bitter taste. This happened to two separate wines from grapes bought on different dates, but from the same supplier. Is there some sort of infection that caused this? Should I throw this wine out?


Senior Member
Jun 10, 2015
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South Louisiana
Sounds like multiple issues.

1. Cool fermentations are poor at extracting color and tannins, and tannin helps retain the color
2. H2S is a result of stress on the yeast, you may not have used enough nutrients
3. Sounds like wine diamonds precipitating out of your wine

This year, try fermenting big reds at a higher temp, mine start at 75 and are allowed to spike to 90. Use some enzymes like Lallzyme EX-V to break down your grapes, and fermenting tannins or oak chips to help bind color. Try to get the YAN on your must to determine the correct amount of nutrients to use, or select a yeast that produces no H2S.

Hard to diagnose a lot more without a lot of info, but it’d be nice to know what yeast you used, what and how much nutrients, what other additives were used, what your processing schedule was (ferment, press, rack off of gross lees, MLF, etc.), and what your numbers were, BRIX, pH, TA, etc. at start and finish.

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