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Wine taking too long to ferment?

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tacomaguy20

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I bought a Juice Bucket of Cabernet and I had it in the primary for a week. Transferred into carboy at 1.006 Specific gravity and in the carboy it's been steadily bubbling but it's been going slow. It's now been just over 4 weeks in the secondary (5 total). It bubbles once every 9 minutes or so. The original fermentation started really early and strong but it's slowed considerably. I haven't tested the gravity again because I wanted to wait for it to finish and didn't want to expose it to more oxygen unnecessarily considering it's got a lot of head space. Was going to rack into a smaller carboy once it stopped. I figure I should just be patient and wait but thought I'd ask the pros. Anybody got any thoughts on this?
 

tacomaguy20

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It will release bubbles for ages. THat isn't fermentation, it's just CO2 coming out of solution. The only way to know your status is to use your hydrometer. I'll bet yours is long complete.
But wouldn't the C02 just escape the wine (displace it) and stay in the carboy's headspace? I assumed the yeast was still going because I thought there needed to be an increase in C02 and the increase in pressure would cause the airlock to bubble. Is that not accurate?
 

NorCal

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The bubbles are due to CO2. The question is if it is currently being generated by the yeast or simply coming out of solution. Without a hydrometer reading and seeing the SG continue to drop, you don’t know for sure. However due to the info you provided, the thought is that fermentation has completed. The remnant CO2 will protect the wine from oxidation, but I would be concerned about other microbial pressure that could spoil the wine without adding SO2 at this point and most likely racking.
 

tacomaguy20

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The bubbles are due to CO2. The question is if it is currently being generated by the yeast or simply coming out of solution. Without a hydrometer reading and seeing the SG continue to drop, you don’t know for sure. However due to the info you provided, the thought is that fermentation has completed. The remnant CO2 will protect the wine from oxidation, but I would be concerned about other microbial pressure that could spoil the wine without adding SO2 at this point and most likely racking.
Okay I'll check it. I just never realized the airlock could still bubble after fermentation had stopped.
 

tacomaguy20

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Okay SG is 1.003 now so I doubt it's done. My other juice bucket of cab (from the same source) fermented dry to .994. The smell is a little harsh but it tastes okay.
 

Booty Juice

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It's moving in the right direction.

I'd rack and SO2 into your long term bulk-aging vessel with minimal head space and proceed per your normal methods.
 

tacomaguy20

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It's moving in the right direction.

I'd rack and SO2 into your long term bulk-aging vessel with minimal head space and proceed per your normal methods.
Wouldn't the S02 make this slow fermentation even worse since the yeast is already having a hard time. I was thinking of adding nutrient to get the yeast going again?
 

Booty Juice

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That's a logical next step.

For me, I don't worry about slow ferments. I've pressed and carboy'd up to 1.020 and always gone dry eventually - but I also use minimal SO2.

Depending on how concerned you are about a bit of RS - another option would be to wait few days or a week and check the SG again before adding nutrients.

If you're wine isn't stinky, I don't see that you a big problem - but I'd get it into a minimal-head-space vessel ASAP.
 

tacomaguy20

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That's a logical next step.

For me, I don't worry about slow ferments. I've pressed and carboy'd up to 1.020 and always gone dry eventually - but I also use minimal SO2.

Depending on how concerned you are about a bit of RS - another option would be to wait few days or a week and check the SG again before adding nutrients.

If you're wine isn't stinky, I don't see that you a big problem - but I'd get it into a minimal-head-space vessel ASAP.
Okay, thank you. I was also told by another member that once I have it in my long term storage vessel I should rerack every 3 months and add S02. Is that what you do?
 

NorCal

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It has gone from 1.006 to 1.003 in 4 weeks.....that is very slow. If it were mine, I’d be concerned about spoilage. If it was good clean fruit and you have no off smells now, you could make an argument to let it keep going. You don’t want to add any more nutrient at this point, as you will be providing food for other organisms which can spoil the wine.
 

Booty Juice

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It has gone from 1.006 to 1.003 in 4 weeks.....that is very slow. If it were mine, I’d be concerned about spoilage. If it was good clean fruit and you have no off smells now, you could make an argument to let it keep going. You don’t want to add any more nutrient at this point, as you will be providing food for other organisms which can spoil the wine.
GOOD ADVICE
 

winemaker81

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How much sediment is there? If it's more than a dusting, rack off it. Gross lees contains fruit solids which start decomposition when it drops.

I learned something new today -- fermentation is always anaerobic. I've been told for years that fermentation in an open container is aerobic while a closed container is anaerobic.

Fermentation (yeast eating sugar) is anaerobic. However, the yeast needs oxygen to reproduce, which is why primary fermentation is normally done in open containers. @JohnT wrote a good summary some years back. A quick search turned up several sites that explained in a lot more detail (including the chemistry). However, John's summary is solid and is digestible by folks who (like me) have no interest in revisiting high school chemistry.

Contrary to popular belief, exposure to air during fermentation is not a bad thing. If it was, we'd be fermenting in closed containers. Post-fermentation is a completely different situation, although brief exposure to the air is no where near the danger that prolonged exposure is. This is why we reduce head space as much as feasible.

Racking the wine may introduce enough oxygen to kick start fermentation. Also, put the fermenter some place warm, e.g., 75 to 80 F.
 

sour_grapes

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Fermentation (yeast eating sugar) is anaerobic. However, the yeast needs oxygen to reproduce, which is why primary fermentation is normally done in open containers. @JohnT wrote a good summary some years back. A quick search turned up several sites that explained in a lot more detail (including the chemistry). However, John's summary is solid and is digestible by folks who (like me) have no interest in revisiting high school chemistry.
WADR, I don't think John's summary is the winner in that thread. I would pay more attention to @spaniel.
 

sour_grapes

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Thanks, I'll review the entire thread.
I should say that I care little about the small semantics question regarding what exactly is meant by an anaerobic fermentation. (I have always used the term the way that John did.) But the part of the discussion that I regard positively concerns when the Crabtree effect is present, and under what conditions the yeast respire aerobically vs. anaerobically.
 

BI81

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Hopefully no one takes this as an attempt to step on their toes... for whatever reason this appears to be a touchy topic.

I’m currently taking a wine production course as part of the UC Davis Certificate program and we had a fairly lengthy review on alcoholic fermentation about a month ago...so I do find the subject interesting and would like to attempt to clarify @winemaker81 post above.

Chemically fermentation is a form of metabolism that differs from respiration in that it doesn’t require molecular oxygen. As @spaniel posted MOST organisms prefer respiration because it is much more efficient. However, S. Cerevisiae & O. Oeni are unique in that they prefer fermentative metabolism, even in the presence of oxygen.

S. Cerevisiae can generate as many ATP/sec as are normally generated by respiration. They’re also osmo-tolerant and can multiply many times without oxygen.

With all of that being said, small (trace) amounts of oxygen favor synthesis of sterols, fatty acids and nicotinic acid. All of which are required for proper yeast cell membrane function. Under normal circumstances oxidation from stemming and crushing is adequate.

(Ronald Jackson, 2020, “Wine Science Principles and Applications, Fifth Edition”, 494-525)
 

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