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Red Wine Fermentation

02/22/2012

Your fermentation should become active anywhere from 1-3 days after introducing your yeast to the must. An important factor in determining how long it will take is the temperature of the must.  Yeast‟s rate of metabolism is directly affected by temperature: cold musts start fermenting more slowly, while warm musts get off to a quicker start. Once the fermentation has begun, the yeast will proceed to consume the sugars in the must/juice, producing CO2 (bubbles) and alcohol. During this period, the skins will be carried upwards by yeast produced CO2 and compact into a large mass that will be pushed up and out of contact with the liquid in the must. This floating mass of skins is referred to as the cap. 

Punching the Cap  

This cap needs to be broken-up and re-submerged several times a day. This process is referred to as “punching down the cap”.  Punching the cap protects the wine, aiding with extraction of color and flavor compounds from the skins, along with the dispersal of built-up heat. If the cap is exposed to the air for too long, the surface can dry out and allow the colonization of airborne bacteria.  The most common one is acetobacter, (vinegar bacteria), though pretty much any one will ruin your wine. Since the rising alcohol levels in the fermenting must are high enough to kill airborne bacteria when it washes over them, submerging the skins helps to protect the wine
from spoilage throughout the fermentation. In addition, mixing also promotes contact between the wine and the skins, aiding color and flavor extraction. The more often the cap is punched the greater the extraction of compounds coming from the skins will be. Finally, fermentation generates quite a bit of heat and the cap acts as an insulator. If not broken up, the cap does not allow the excess heat to escape, causing the fermentation to become  too hot.  Try to avoid elevated fermentation temperatures because they antagonize yeast and cause fermentations to stick, as well as produce off flavors and aggressive qualities in the final wine.  
 
*Note: It is important to get all of the lees (the layer of yeast that settles out on the bottom of the fermenter) stirred back up into suspension with every punch-down cycle. You are looking for the must to become pink and creamy. This allows the fermenting wine to expel many negative fermentation odors that are a natural product of fermentation. It also helps to keep the wine from developing sulfur problems. However, it is important to avoid mashing or grinding the seeds as much as possible during the punching as they contain harsher, more astringent tannins and their release could make the final wine more aggressive and unpleasant.  
 
How to Punch the Cap  
MoreWine! offers several models of punches to accommodate a variety of fermenter sizes from 30 gallon plastic food-grade bins to 600 gallon stainless steel tanks. They are made of durable food-grade metal and are easily sanitized and cleaned after each use. Of course, any object made of food-grade material can work as a punch down tool, as long as it can move the skins back into solution and stir the lees. It is a good idea to make sure the material can be sanitized, however. Food grade plastic or stainless steel is great, but wood is not, due to its porosity.

 

Yeast Nutrition During Fermentation  

As the fermentation progresses, the must becomes a more difficult place for the yeast to work in: the alcohol level starts to rise (slowly becoming more and more toxic) and the original nutrients have been depleted. The Go-Ferm addition we made when hydrating our yeast was only designed to get them through the hydration process. Yeast require more nitrogen, amino acids, micro-nutrients, etc. in order to stay healthy during fermentation. When those nutrients are not present in sufficient amounts, yeast produce off flavors (such as Hydrogen Sulfide and VA) and have difficulty finishing fermentations. In order to avoid this scenario, we provide the needed nutrition in the form of a complete specially formulated yeast nutrient that gets added to the must during the fermentation.  
 
That said, hundreds of people have told us:“I never used any nutrient and my wine was fine.” Yes, that can certainly be true. However, by feeding the yeast during fermentation, you can easily avoid the most common problems in winemaking, such as Hydrogen Sulfide (rotten egg smell) or VA (Volatile Acidity) production, stuck ferments, and various other off flavors. Studies have shown that even in wines with no fermentation problems, the ones with the full nutrient supply made better flavors and aromas than the musts utilizing no nutrient additions. Using nutrients is a cheap and easy insurance policy that always makes a positive difference.  
 

Fermaid-K (AD345):                                                                                                                      
To complement your Go-Ferm addition once fermentation has started, we suggest using Fermaid-K, a complete yeast nutrient also made by Lallemand. Fermaid-K is usually applied at the beginning of the fermentation (cap formation) and again at 1/3 sugar depletion (usually an 8-10 ºBrix drop). A double addition supplies the yeast with enough nutrients to maintain a healthy metabolism throughout the fermentation. In a warm starting fermentation, an 8-10 ºBrix drop may take place in the first two days, so be sure to check your ºBrix early on Day 2. Some winemakers choose to add Fermaid-K in smaller amounts on a daily basis, usually starting on day 1. This is also a fine approach. However, yeast will utilize few nutrients after 10% alcohol. (a 15 ºBrix drop) Additions made after 10% alcohol may only serve to feed spoilage organisms. (Note: 1 g/gal Fermaid-k = 25 ppm Nitrogen)
 
DAP (Di-Ammonium Phosphate) (AD330)
DAP is a traditional yeast nutrient that is still widely used. However, DAP is solely a non-organic source of nitrogen – it offers no additional nutrition. DAP should be only considered a supplement to a complete nutrient set when a must is known to have a low nitrogen content*. DAP does make yeast grow and produce more cells, but it does not feed them. A good analogy here would be to say that Fermaid-K is a bowl of fresh fruit salad that is chock full of vitamins, minerals and natural sugars, and DAP is a packet of high fructose corn sugar, offering quick energy but no nutritional value. (*Note: “Yeast Available Nitrogen”, or YAN can be analyzed by a lab and this will tell you how many ppm Nitrogen you have. Ideally you want around 250 ppm Nitrogen in the must at the start of the fermentation. If your Nitrogen is below 250 ppm, you can use DAP to raise the amount up to this level: 1 g/gal DAP = 50 ppm Nitrogen).

If a ferment is suffering from a lack of nutrients and making H2S, there is a deficiency of nutrients available per yeast cell. Adding DAP would not feed them, it would only increase the number of starving cells.  It does not make sense to increase the population in a famine zone. You should use a complete nutrient set instead of DAP to address and avoid H2S problems during fermentation.  
 
If you are using Fermaid K, which contains DAP as one of its ingredients, there should be very little reason to use DAP separately.
 
For complete information on Yeast Nutrients, see our guide to yeast rehydration
 
 
Fermentation Temperature
 
Every winemaker has a theory on what temperature to ferment at.  We have seen great wine fermented from a variety of different temperature schedules. You should pay attention to the temperature. It's definitely a good habit to note the temperature of the must each time you punch down the cap (a good way to do this is to use a floating thermometer (MT400)) for future reference. The actual act of fermentation produces heat and can cause the must to be 10°-15° F higher than the ambient temperature.  
 
A Typical Temperature Schedule  


If you have control over fermentation temperatures, a popular red wine schedule is to start slowly at cooler temperatures, such as the low 60s. Next, gradually allow the must to warm up to the desired temperature as the fermentation gets underway. Starting cold allows water-soluble compounds in the must such as anthocyanins (color) and agreeable tannins extra time to become fully extracted improving the final wine.  
 
During fermentation the temperature is allowed to rise, often reaching 80°-90° F for a brief period of time. Yeast create different compounds at different temperatures.  How high you allow the fermentation temperature to rise or “spike” is often debated. Some winemakers allow it to go into the low 90‟s. However, alcohol toxicity increases as the temperatures rise, so spending too much time in the upper temperature ranges can be damaging to the yeast and they may have difficulty finishing the fermentation. We recommend limiting the spike to the mid to upper 70‟s for safety‟s sake. Most winemakers agree that a temperature range of 70°-85° F is acceptable.  
 
Controlling Temperature  

There are two main methods of temperature control, both with advantages and disadvantages.  The most serious home hobbyist purchases a small glycol cooling  system such as our GLY100 which can precisely dial in temperatures. They work by circulating cold water or water/glycol mix through a jacket around the tank or a cooling snake/cooling plate submerged in the fermenting must.  The only problem with these systems is that they're relatively expensive.  They provide piece of mind, but at a price.  The second method only involves investing in some plastic jugs. To use, freeze the jugs, then pull them out of the freezer when the must gets too hot. Sanitize the jugs and float them in the must, stirring until the temperature drops to where you want it to be. Keep in mind that you might want two sets of jugs, one for the must and onefor the next round. In general, the “hot” portion of the ferment only lasts for a few days, and life will soon return to normal. However, if you happen to live in a very warm climate or will have warm ambient temperatures when you will be fermenting, you may want to speak with us about your options for a dedicated temperature control system. 

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