Ah yes, the mid-ferment stall . . . so common, yet always a bit of a heart-stopper. When fermentation slows or stops around 5 °Brix, it’s usually a sign your yeast are running out of steam. Stress accumulates as alcohol rises, temperatures fluctuate, nutrients deplete, or the pH creeps outside the comfort zone. The yeast may have started out strong but are now fatigued and struggling to finish the job.
Red wines like Syrah are especially prone to this because they often ferment hot and fast early on, then cool as the sugars drop and fermentation slows. It’s easy for a must to quietly drift from 80 °F (27 °C) to 65 °F (18 °C) without noticing, and this change is enough to cause some strains to stall — especially if they’re already under pressure from high alcohol or low nutrients. This is one reason many winemakers keep an eye not just on sugar and temperature, but also on the nitrogen content of the must before fermentation starts.
Nutrient depletion is a major cause of sluggish ferments. If your grapes were low in yeast assimilable nitrogen (YAN), and you didn’t supplement early on with a complete nutrient blend, the yeast may have simply run out of fuel. It’s especially important when using strains known for high fermentation vigor as these can have high nutrient demands. Rehydration nutrients can help yeast build healthy cell walls right out of the gate. Later, staged additions of Fermaid K or Nutriferm Advance (Enartis) during fermentation can prevent crash-outs by feeding the yeast exactly when they need it most.
There’s also alcohol toxicity to consider. Many Syrah musts start around 25–26 °Brix, which puts your final alcohol near 15% if it ferments to dryness. Not all yeast strains are built for that. Some will stall naturally around 14% unless you’ve selected one with high alcohol tolerance. For future ferments, you might explore robust strains like Uvaferm 43 (Lallemand), Fermol Premier Cru (AEB), or EC-1118 (Lalvin/Scott Labs), all of which are known for strong performance under challenging conditions.
Your pH could also be playing a role. If the must pH is too high — say, above 3.8 — yeast can behave sluggishly, and spoilage microbes may become more competitive. If you haven’t already, check your pH and consider a tartaric acid addition to bring it down closer to 3.6–3.7, giving the yeast a more favorable environment and improving microbial stability.
Since your fermentation has been stalled at 5 °Brix for several days, and warming and nutrient additions haven’t restarted it, you may need to consider building a yeast starter to re-inoculate. This isn’t something to do hastily. You’ll want to use a strong, alcohol-tolerant strain like the ones mentioned earlier, hydrate it carefully with Go-Ferm, then gradually acclimate it to your wine’s alcohol by adding small portions of the stuck wine over time. Once the culture is bubbling and fully adapted, you can add it back into the full batch.
Rather than outline every detail here, I recommend reading the previous WineMaker article “Restart Stuck Fermentations” by Bob Peak. It offers excellent step-by-step guidance, including how to build and scale a starter culture properly.
Looking ahead to your next vintage, prevention is key. Before inoculating, consider testing your must’s YAN and pH. Choose a yeast strain appropriate to your Brix and desired wine style. Always rehydrate dry yeast with nutrients to support healthy cell development and stagger your nutrient additions to give the yeast what they need when they need it. Daily Brix readings (two or even three times a day during the peak of fermentation) and temperature tracking will help you catch slowdowns before they become full-blown stalls.
Stuck fermentations are frustrating, but they’re also one of those winemaking moments where you gain a lot of practical knowledge fast. With the right tools and a bit of patience, I hope your Syrah finds its way to dryness — and that you gain confidence for whatever challenges next year’s harvest brings.
