By Eric R. Mentzer
This is my David Letterman approach to helping you avoid having a fermentation failure. The following list is the top 10 reasons for having a slow or non-existing fermentation. They are listed in order from most common to least common.
1. The Fermentation Temperature is too Hot or Too Cold:
Wine yeast like to ferment between 70-75 degrees Fahrenheit--72 degrees being ideal. Fermentations that are too cool may become very sluggish and quite often will not ferment at all. Fermentations that are too warm can perform poorly as well. And in extreme cases--85 degrees and above--the wine yeast cells may become damaged, inhibiting their ability to ferment.
It is also important to note here that fermentations that are too warm are more hospitable to the growth of unwanted micro-organisms. This could result in off-flavors in your wine and in extreme cases complete spoilage.
Having a consistent temperature throughout the fermentation is important as well. Room temperatures that fluctuate on a daily bases can play havoc on a yeast's ability to ferment. Simply put, the more the room temperature fluctuates, the more likely you are to have a problem fermentation.
Avoid trying to ferment your wine in places such as detached garages, attics or spare bedrooms where the room temperature can easily be ignored or not controlled at all.
If your house has a basem*nt, it is usually one of the better places to ferment your wine. Basem*nts typically maintain a temperature that is more constant than the rest of the house.
However in the winter months, basem*nts can become too cool. If this becomes the case, a mild heat source such as a nearby light bulb may be enough to solve the problem. Also try to keep your fermentation vessels up off the cold basem*nt floor. Instead, keep your fermentation vessels elevated on a table or shelf.
One way to keep a handle on your fermentation temperature is to use a thermometer. If you are using a pail as a fermentation vessel, you can use a floating thermometer directly in the wine. Just lift it out when you want to take a reading, otherwise it stays in the juice.
Or, you can use a crystal strip thermometer which sticks to the outside of the fermentation vessel. The temperature illuminates by what appears to be magic. Just a quick glance and you are able to tell the temperature of your fermentation.
2. Adding Too Much Sugar:
Yeast needs sugar to produce alcohol, but too much of a good thing can be bad. When sugar concentration levels are too high, the sugars stops acting as a food source for the yeast and When a fermentation occurs what is really happening is the wine yeast is consuming sugar and turning it into alcohol. So the amount of sugar that is available to the wine yeast controls how much alcohol that can be made. But contrary to reason, it is possible to have too much sugar in a fermentation.
If the sugar concentration level of the must becomes too high at any given point--either at the beginning or during the fermentation--it starts to have an inhibiting effect on the yeast's ability to produce alcohol. In other words, the higher sugar concentration starts to act as a preservative effecting the fermentation in a negative way.
Before you add sugar to a batch, it is necessary to know how much sugar is already being provided by the fruit. This can vary dramatically from one fruit to the next. For example, in the case of most California grown grapes, no sugar is required at all to produce a wine with a reasonable level of alcohol--say 10 to 13 percent--but when making berry wines a considerable amount of sugar is required to obtain those same levels.
If you have a good wine recipe from a reliable source, such as a wine making book, you can normally depend on the amount of sugar the recipe is calling for. Or certainly if you are following directions that were provided with wine making kits, your sugar level should be no issue whatsoever, just follow the directions.
But if you have a recipe from a questionable source or you are going it alone, it is strongly recommended that you control your sugar levels with the aid of a wine hydrometer, or find a reliable, trusted recipe.
A wine hydrometer can tell you how much sugar is already in the must as well has how much sugar to add to end up with a potential alcohol level that is desirable.
It does this with a scale that is called "Potential Alcohol." The more sugar that is in the must, the higher the percentage reading will be on the Potential Alcohol scale.
For more information about the hydrometer and its use, see the following article on our web site: "Getting To Know Your Hydrometer."
At the beginning of fermentation, having a "Potential Alcohol" reading higher than 13% will usually interfere with the yeast's ability to start fermenting. Realize that most all wines you buy commercially are between 10% and 13%, so this is really no big issue.
But there are some of you out there--and you know who you are--that seek to drive the alcohol as high as possible. This is okay, but it is necessary to feed some of the sugar throughout the fermentation instead of adding all of it to the must up front.
By feeding sugar in this way you will be able to achieve higher alcohol without getting your sugar concentration levels too high. You are giving some of the original sugars time to turn into alcohol. This in turn will make room for the additional sugars you are feeding.
If you do not feed sugar in this way when attempting to achieve higher alcohol levels, you will be setting yourself up for potential fermentation problems.
3. Improper Yeast Starting Method:
Many packets of wine yeast instruct the user to re-hydrate the wine yeast in warm water for a few minutes before using it. Re-hydration is just a fancy word for moistening the wine yeast.
When following these directions perfectly there are no problems, but quite often we run into situations where the winemaker's water temperature that was used for re-hydration was just a little too warm or the wine yeast was left in the water for too long.
The recommended temperature on the packets of wine yeast we have seen is 95 to 105 degrees F. for about 15 minutes. Believe me when I say these directions give little room for error. For every minute the wine yeast stays a 105 degrees a small portion of the yeast cells are being destroyed. If the water is just a little hotter, say 115 degrees, then the yeast cells are being destroyed at an alarming rate.
So what this means to the home wine maker is that if they rehydrate their wine yeast at too warm of a temperature, or if they keep the wine yeast in the warm water for a longer period of time then recommended, the cell count may become too low to support a proper fermentation.
When preparing the water for re-hydration I recommend always verifying the water's temperature with a wine making thermometer before adding the wine yeast, as well as tracking the amount of time the wine yeast is to be in the water.
Secondly, I also recommend that you shoot for a temperature no higher than 90 degrees and keeping the wine yeast in this water for no longer than 10 minutes. The 90 degree temperature for 10 minutes is plenty to complete the re-hydration process and will result in the destruction of less yeast cells.
To be more frank, if the re-hydration process was skipped entirely it would not be of great detriment to the wine. The yeast would simply take a little longer to start fermenting. Basically this means instead of seeing the first signs of activity in 2 to 4 hour, without re-hydration it might take 4 to 8 hours.
4. Sealing Up the Fermenter After Adding Sulfites:
Most wine making recipes instruct the winemaker to add sulfites such as Sodium Bisulfite or Campden Tablets to a starting must. These sulfites are added to the juice 24 hours before adding the wine yeast as a sterilizing process. The sulfites are released into the juice destroying any molds or other contaminants that may be present, wild yeast included. This allows the winemaker to start his fermentation off with a clean slate, so to speak.
Once the sulfur has been added to the juice, it slowly starts to dissipate into the air in the form of a gas and eventually all goes away. This process usually takes between 18 and 24 hours. After the 24 hour waiting period, the winemaker can then safely add fresh, domesticated wine yeast without fear of it being destroyed by the sulfites.
It is important during this 24 hour waiting period that the juice is allowed to breath. That is, to allow the sulfites to escape. The fermentation container should not be sealed up or even fitted with a wine airlock, but rather, it should be covered only with a very thin towel, at best. This is simply to keep foreign matter from getting into the juice.
If the sulfites are not allowed to dissipate into the air during the 24 hour waiting period, then it is highly likely that most of the wine yeast will be destroyed when it is later added to the juice. The result is a fermentation that is very sluggish or one that will not start at all.
5. Using an Airlock During the Primary Fermentation:
During the first few days of a fermentation, the wine yeast is in a multiplying stage. It is devoting a significant portion of its energy to reproducing itself. On average, the wine yeast will multiply itself to around 100 to 200 times the amount of wine yeast you originally put in the must.
This is known as the "Primary Fermentation." Later, once the yeast has fully created the number of cells needed, it will then devote most all of its energy to creating alcohol. This is known as the "Secondary Fermentation."
The cell reproduction stage is necessary to successfully sustain a healthy, vigorous fermentation. If the wine yeast does not multiply successfully then the remainder of the fermentation will become sluggish and drawn out, and in many cases the wine yeast will give out completely before it has completed the task placed before it.
For the wine yeast to be able to multiply itself to its fullest ability, it needs air during the primary fermentation. Using a Wine Airlock during this time seals the fermentation from much need air, in effect, suffocating the wine yeast and putting a damper on its reproductive activity.
Instead of using a Wine Airlock during the Primary Fermentation, simply cover the container with a thin towel, cheese cloth or something similar. You can secure it by tying it down with a string to make sure it doesn't get knocked or blown off. By doing this you will allow the wine yeast to get all the air it needs without allowing bugs and other little nasties from getting in the mix.
After about 4 to 6 days of fermentation the wine yeast will go into its slower, secondary fermentation. This is the time when the wine airlock should be used. The air is no longer needed, and in fact, is a detriment to the must at that point.
6. Lack of Nutrients:
Having sufficient nutrients in a must is an integral part of any successful wine fermentation. Without nutrients the wine yeast is unable to perform to its fullest ability. The result is a wine fermentation that is sluggish and quite often, one that will stop altogether--before the fermentation is complete.
The typical nutrient-deficient fermentation will usually struggle along with some success for the first few days and then seemingly hit a brick wall, ceasing all but an insignificant amount of activity. This scenario occurs primarily because the wine yeast is able to consume the simplest sugars that are available without much nutritional need. But as the simple sugars are used up and the preserving effects of alcohol starts to increase, the wine yeast cells end up simply "meeting their match".
Another reason the wine yeast will stop in mid-fermentation, is that the little amount of nutrients that were available to the wine yeast are now gone. The wine yeast actually consumes them, leaving the must that was just short on nutrients, now with next to no nutrients at all.
When making wine from grape juice, either fresh or packaged, nutritional needs are easily met by simply adding what is known to home winemakers as "Yeast Nutrient" or "DAP" which stand for Di-Ammonium Phosphate.
There are two reasons why nutritional needs are fully met so easily when fermenting wine from grapes. The first being that wine yeast are specifically developed with grape juice in mind. The various strains of wine yeast are actually developed in a grape juice environment so as to acclimate them to grape juice. The result is wine yeast strains that are very happy with the set of nutrients that grape juices typically provide.
The second reason is that when making with grape juice, very seldom is the juice diluted with water. So the nutrients from the grape juice are at full strength as well. Even when making wines from concentrated grape juices, this holds true. The concentrates when diluted back to their original volume, contain a same wealth of nutrition as they did before being processed.
The only thing you can really do to improve the set of nutrients in these grape juices is to add "Yeast Nutrient," as mentioned earlier. This product adds both nitrogen and phosphorus to a fermentation. You can kind of think of it as adding fertilizer to your wine yeast.
Unfortunately, when making wines with most other fruits the plot thickens a little. When making wines from berries, plums and the like, having ample nutrition in the right balance for the wine yeast is a significant issue that needs to be addressed.
With these types of wines, the nutrients that are naturally provided by the fruit may not be of the balance or type that wine yeast needs to perform to their maximum ability. Also with these wines, the juice almost always needs to be diluted significantly with water and sugar. This in turn dilutes the various vitamins, proteins and minerals as well.
When making these types of wines a more well rounded set of nutrients is required. One that not only provides more nitrogen and phosphorus in a simple form such as Yeast Nutrient, but one that also provides proteins, minerals and vitamins in a proper balance. Such is the case with "Yeast Energizer."
Yeast Energizer is designed specifically for nutritionally aiding the fermentation of everything from berries to bananas. It contains a blend of nutrients that helps to fill the nutritional voids that some recipes can create.
One way to know if Yeast Energizer is needed in a wine you are making is by giving it a simple test. Ask yourself, "how close is the produce I am using to a grape?" The closer the produce is to a grape, the less likely you will need to use Yeast Energizer. For example, a currant wine is much less likely to require Yeast Energizer than say, watermelon wine.
Another way to know is by simply following a recipe. Most recipes will indicate if "Yeast Nutrient" or "Yeast Energizer" is required. There really is no reason to second guess a wine recipe that indicates a specific type of nutrient. Just the fact that the wine recipe calls for a nutrient of any kind, usually means that it is probably from a sound source.
As a final note, there are some produces that put a tremendous strain on the yeasts' ability to ferment. Some of these would be things like honey, dandelions and vegetables. With these types of produces, nutrients may be plentiful, but they are not of the kind wine yeast need. When fermenting these types of musts, I recommend not only using Yeast Energizer, but also using something called "Ghostex" along with it. Ghostex enhances the yeasts' ability to multiply itself. This gives the yeast a fighting edge when it comes to completing a fermentation.
7. Fermentation is Already Done:
In a twisted way, you may not be getting a fermentation because the fermentation has already completed. Many beginners ask, "how could this be?" It's almost like experiencing an unbelievable magic trick. "How did my wine do that?" But, after checking the wine with a hydrometer, the truth becomes clear. The juice fermented, and you didn't even know it.
Relax, its really not your fault. And, there's really no problem, anyway. Most wine making directions you run across will lead you to believe that all fermentations will take anywhere from 4 to 6 weeks. But in reality, if the conditions are right, a fermentation can complete in as little as seven days. Yes, that's right "seven days." I personally know of fermentations that have completed in as little as five days, but this is far more rare.
The only real way to know where you stand with your fermentation's progress is to take a hydrometer reading. The hydrometer has the final say as to what has actually happened. If you take a hydrometer reading and you discover that the Specific Gravity is 0.998 or less, well then, yes, the wine is done fermenting. If this is the case, there is really nothing else for you to do other than continue on with rest of the directions ahead of schedule.
Many first-time winemakers will get the notion that they should add more sugar if there fermentation completes quickly. If you have added the correct amount of sugar at the beginning of fermentation, this would not be the right thing to do.
Just because a fermentation only lasted a week or so, does not mean the wine has any less alcohol than a fermentation that took 2 months. Time does not control the amount of alcohol made, the amount of sugar available to the wine yeast does. Adding more sugar at this point will only complicate the situation.
For example, if your starting hydrometer reading indicates that you have enough sugar in the must to produce 12 percent alcohol, you will have 12 percent alcohol once all those sugars are fermented, regardless of the amount of time it takes. And, you will know when all those sugars have been fermented by the fact that the hydrometer reads 0.998 or less on the Specific Gravity Scale.
Many beginners ask, "why does this happen?" The fact of the matter is, there are many reasons why a fermentation might go fast or slow. There are an endless number of variables that can come into play when dealing with Mother Nature. But having said this, a large percentage of the time it is temperature related.
All things being the same, musts that are 75 degrees F. or higher will ferment much faster than a must that is 70 degrees F. or less. The amount of wine yeast that is pitched into the must can make a difference. Two packs of wine yeast will ferment the same juice, not twice as fast, but faster that one pack of yeast will.
If the yeast is pre-started ahead of time, this can influence the rate of fermentation as well. Not only does pre-starting the wine yeast allow the yeast cells to hit the juice with their feet running, so to speak, but it also allows the yeast to multiply in number, ahead of time, which could contribute to having an explosive fermentation.
Having a fast fermentation is neither a good thing or bad thing. But the reasons that caused it to ferment fast may be bad. For example, if you had a fast fermentation that was caused by warmer temperatures, this could be bad. Having too warm of fermenting temperature will also facilitate the growth of unwanted micro-organisms, which may give the wine an off-flavor. But, if you had a fast fermentation because you pre-started your wine yeast, then no harm is done.
Having said this, there is really no advantages to having a fast fermentation in of itself. Of course you get to bottle your wine sooner with a faster fermentation, but I know of no studies that have indicated "fast" is better or worse than "slow".
8. Yeast Has Reached its Limits:
One thing that must be understood when making wine is that alcohol is a preservative. By definition, a preservative is something that helps a perishable to remain in its current state--to not change, but remain as is. How this translates to wine making is that the alcohol itself can be the reason a must is no longer fermenting.
Musts that are just beginning fermentation and are still at lower levels of alcohol concentration, say 5 percent, do not experience much problem hosting a fermentation. But, as a must's alcohol level rises, one will usually begin to notice a slowing of the fermentation activity. This slowing is primarily due to the increased preserving effects the rising alcohol is having on the must.
And, as the alcohol level continues to rise throughout the latter part of the fermentation, 10-12-14 percent, the fermentation becomes slower and slower until it simply can no longer overcome the increasing effects of the alcohol.
To put an analogy to this, if you have ever seen a tractor pull, you can think of a fermentation as a single pull. It takes off with little hesitation, but as it grinds on further and further and the resistance from the weighted trailer becomes greater and greater, there comes a point when the wine yeast can't pull any more and it simply has to shut down.
And, it will shut down regardless of how much sugar may be left in the must. So, it is possible for a must to have more sugar than the wine yeast can turn into alcohol, resulting in a wine with significant alcohol but way too much sugar to be drinkable.
Using a hydrometer is the key to knowing how much sugar can be safely added to a wine recipe. By using a hydrometer you can add the correct amount of sugar to a wine recipe to shoot for a specific alcohol level that is reasonable and achievable.
Expect wine yeasts to produce up to 12-13 percent alcohol with minimal effort, this is assuming that all other environmental conditions for the yeast are optimal, such as: temperature, nutrients, and so on. Anything beyond 13 percent, you're on your own.
If you want to experiment with producing higher alcohol wines beyond 13 percent, you will want to carefully read the article, "Making High Alcohol Wines" listed below.
9. Using Distilled Water:
Using bottled water when making your wine is fine, and in some cases preferred, depending upon what's in your tap water. But, not all bottled waters are the same. Some bottled waters have been distilled and that's a bad thing for winemakers. When choosing bottled water for wine making be sure that it is labeled as spring water, mineral water or some kind of drinking water and not labeled as distilled water.
Using distilled water can cause big problems for the unsuspecting winemaker. There are two reasons for this. The first being distilled water has had all of the excess or "free" oxygen removed from it. The second reason is that distilled water has no minerals either. Both of these conditions are direct results of the distilling process and both conditions have inhibiting effects on a fermentation.
During the primary fermentation the wine yeast need an ample supply of oxygen in the must to allow them to freely reproduce themselves. The yeast has the monumental task of multiplying themselves to around 100 to 150 times during the primary fermentation. If the yeast are not given enough oxygen to multiply successfully, then the result will be a sluggish fermentation that can drag out for several additional weeks.
Having no minerals in the water affects the fermentation in a negative way as well. Minerals are a significant portion of the nutritional meal that is required by the yeast to perform at their best. Different minerals effect the wine yeast in different ways, but in general, minerals increase the yeast's ability to metabolize or consume sugar. Without a supply of minerals you have yeast that consume sugar at a slower pace.
10. Yeast is too Old:
If you have a must that has started fermenting very slowly or hardly at all, one of the many things you need to ask yourself is, how long have you had the wine yeast, and how was it being stored during that time.
Wine yeast is a living organism that has a limited life-span just as any other living thing would. When you purchase yeast it comes conveniently packaged in a suspended, freeze-dried state. When the dried wine yeast is put in a liquid it rejuvenates itself back to its original, natural state.
While the wine yeast is in freeze-dried form it can become old, however it does not do so all at once, but rather, slowly over time. The average 5 gram package of dried wine yeast contains roughly 150 billion yeast cells. More than enough to produce a healthy, vigorous fermentation in a 5 or 6 gallon batch. Even 75 billion active yeast cells would be more than sufficient to ignite a very active fermentation.
A portion of these cells die every year, every month, and even every day. If you store your packets of wine yeast at room temperature, it will be active enough to use for at least 1 year. If your yeast is being stored above 80 degrees F., then its useful life-span will be shortened accordingly.
If you store your yeast in the refrigerator, your yeast will be fine for at least two years. It is important to note here though that you should never store your yeast in the freezer. The cell walls of the yeast actually become damaged from the effects of freezer-burn.
So, the whole point here is to be aware of the age of yeast packets you have on hand. Understand that these packets of wine yeast will not be usable forever and may be one of many possible reasons for having a fermentation that will not start.
I hope this helps you out. There are many more potential reasons why a fermentation won't start, but in my experience these 10 reasons cover over 95 percent of the situations we run across. Also, realize that it may be a combination of more than one of the above.
