Wine Talk

Snooth User: juls31

Fermentation failure

Posted by juls31, Jan 8, 2016.

I am not a winemaker and know little about winemaking but I just wonder what could be the main reasons of fermentation failure.

Replies

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Reply by outthere, Jan 8, 2016.

The question is too vague. We need more details. It's akin to asking what causes a cough.

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Reply by juls31, Jan 11, 2016.

I have been hearing of wine fermentation which has been completed in five days though fermentation generally takes about four our six weeks , this will lead to fermentation failure if unnoticed. Is that true? how could it be possible?

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Reply by outthere, Jan 11, 2016.

Primary fermentation usually happens over the course of a week but notice I said "usually." Sometimes getting the last 3-4% of RS to ferment can stall and take a few weeks but that's the exception rather than the rule. Problems occur when winemakers are not paying attention and if they aren't paying close attention during fermentation they are not doing their job. Brix and pH readings should be taken twice a day during this time. Once in barrel things still need to be watched over to be sure primary fermentation completes and malolactic fermentation occurs. If something goes unnoticed it is because of poor/lax winemaking.

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Reply by juls31, Jan 12, 2016.

Some people said that it is due to the hydrometer scales which are often confusing but I do not really agree with that. Hydrometer is a very useful tool for winemakers meaning that it will never fool or am I wrong saying so?

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Reply by JonDerry, Jan 12, 2016.

Listened to an IDTT (I'll Drink To That) podcast recently featuring John Kongsgaard. He had an interesting technique for fermentations, supposedly similar to the Burgundian model in the 80's, with no inoculation, the wait being about a week before fermenting begins, and he explained how sometimes the malo will start before the alcoholic fermentation is complete, so both the bacteria and yeast are competing for nutrients.

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Reply by Richard Foxall, Jan 12, 2016.

Google "stuck fermentation" and you can learn everything you would ever want to know about it.  A hygrometer is something that measures sugar content by measuring specific gravity of the grape juice, to simplify.  There are three systems commonly in use--Brix in US, Baume in France, Oechsle in German speaking countries.  By themselves, the scales have no impact on fermentation--any more than using metric or British units have any impact on whether your furniture fits through the doorway.  They are just measuring systems.

Short answer is that contamination, inadequate nitrogen (in the must), insufficient amount/vigor of the yeast, improper temperature (heat kills the yeast, cold makes it inactive) account for nearly all stuck fermentation.  There are also yeasts that cannot survive if alcohol reaches a certain level--this is now a problem when riper fruit is used, but it's somewhat less common. 

Kongsgaard doesn't have a "technique," he's doing what wineries used to do all the time and all the ones who use "native yeast without inoculation" do.  It's relatively common for MLF and primary to happen at the same time, but more common for primary to happen first.  However, there's not that much worry that they compete for the same nutrients:  If malo only relied on the sugars yeast used, how could it happen in dry wines with no RS?  Turns out that the bacteria can consume pentoses, which yeast cannot.  Yeast can use sucrose, which 45% of MLF bacteria cannot.  So they compete for only fructose and glucose.  I would think that MLF and primary together might reduce ETOH in some of these overripe grapes, but the downside, if MLF bacteria outcompeted, would be too much lactic acid, which can be a fault, too. 


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