Five Steps to a Successful Fermentation: A Beginners Guide

Yeast is designed by nature to ferment fruit juice, especially grape juice. Yeast enjoys the acidic medium, the plentiful sugar and the nutrients that are within the grape berry. So, why is it so hard to start and complete a successful fermentation? Perhaps it’s because yeast is not interested in creating “great” wine or the wine you have in mind when you, with great expectation, add that packet of yeast into your juice. Yeasts just want to have fun!

The trick to great wine is first and foremost to have a clean and complete fermentation. In order to develop and maintain the fermentation, yeast must be stewarded through stages in the life of a fermentation, from birth, early days and eventual death. To become a successful winemaker, you must master this process. It seems overly obvious, but quality wine is really made in your fermenter. So, ignore the mechanics of fermentation at your peril. This article will discuss the five steps to start, maintain and finish a fermentation.

Rehydration

Rehydration is not as simple as it seems. Opening the yeast packet and chucking the dry yeast into the juice will not get you a stress-free fermentation, nor possibly any fermentation at all. Most yeast is sold freeze dried. This dry powder is not ready to start a fermentation from the packet. The individual yeast cells must be “re-born” and must be allowed to mature enough to withstand the hardships of a high acid and high sugar medium. As part of this process the baby yeast cells develop a protective membrane around the yeast cell. The best way to prepare the yeast is to use warm distilled water and a yeast starter such as Go Ferm, or similar product on the market. Allow the yeast to develop over the time listed on the yeast packet, about 13 to 15 minutes.

Once this time is passed you can use it to inoculate your juice or must, if the juice is ready. But I like to make a starter batch using a small amount (a tablespoon or so) of un-sulfated apple juice as I get the must or juice ready for inoculation. Allow the yeast to be exposed to oxygen, as that will also be needed by the yeast to reproduce. After an hour or so, you may notice the starter batch to begin producing bubbles. That is a good sign.

Inoculation

Your yeast is ready to go, but your juice or must may not be ready to ferment. This is one reason I like to create a yeast starter, as it gives me time to attend to this important step. If you have obtained juice, it may be kept in a very cold holding tank to clarify and store. It will also be sulfated to keep it free from unwanted fermentation or from spoilage bacteria. You will want to know how much sulfite has been added, as it deters fermentation. Usually it’s a manageable amount at 50 PPM. That lessens quickly in sulfated juice and should be no problem to your fermentation. If it’s significantly more than that, you may want to rack the juice to lower the free SO2.

Very cold juice from a storage tank could kill, reduce the number of yeast cells, or otherwise hinder your yeast. It would be like throwing a baby into an ice bath. Wait until the juice warms up to room temperature before adding it to the juice or must.

This is also the time to check and adjust your sugar levels and acid levels. You must know your initial sugar level to determine the wine’s final alcohol level. Adjusting sugar levels up or down must occur before fermentation. Acid levels can be adjusted after fermentation, but it’s easier to do major acid adjustments early. Tartaric acid can be integrated into the must. To reduce acid levels after fermentation, use potassium carbonate as calcium carbonate takes a very long time to settle out.

If you are considering using a malolactic bacteria addition to reduce malic acid to the softer lactic acid you may co-inoculate with your fermentation yeast. Many winemakers choose to add the bacteria after completion of the sugar fermentation, some with sugar fermentation.  If co-inoculating, you must do so after one day of fermentation and no later. If not at that time, then wait for fermentation to finish. This avoids the two fighting for nutrients and creating a stuck (stopped) fermentation for both sugar and malic acid. Use a malic activation starter and specifically designed malic bacteria nutrient. Sugar fermentation nutrient will be discussed below.

Maintain & Monitor

Once you have inoculated the juice and fermentation has begun, it’s important to monitor the fermentation on a daily basis, especially monitoring the sugar level. The yeast will need some added nutrient at some point. Without the added nutrient, the yeast may start to cannibalize other yeast cells to provide the nitrogen needed to replicate. This can lead to stinky wine which smells like rotten eggs.

A balanced approach to fermentation nutrition is recommended. Adding too much nutrient too early can cause the yeast replication to explode using up all the nutrients in the must. This causes fermentation to stop. It’s like using up all the oxygen in a room. The standard approach  to add additional nutrient is after one third of the sugar is depleted. DAP (pure nitrogen) can be used, but a balanced nutrient product, such as Fermaid K or Fermaid O (organic) is recommended. This gives the yeast an opportunity to grow in a measured way, rather than the yeast bingeing on nitrogen, a bit like a sugar high. It’s like waiting 5 or 6 hours after lunch to have dinner, when you would naturally be hungry.

My approach to adding nutrient is a little different. The standard approach assumes there is enough nitrogen in the must to sustain a beginning fermentation. Professional winemakers know exactly how much assumable usable nitrogen is in the juice or must and add additional nitrogen if deficient. This nitrogen is called YAN. Most of us amateur winemakers do not know the YAN content in the must. My practice is to divide the nutrient addition into two parts, one half at inoculation and the balance at one third reduction in sugar.  

After a few days, the fermentation should be roiling, with lots of bubbles and yeast foam. It’s about that time when the sugar is one third depleted. I like to use an open container for my reds and whites alike. This allows for active stirring adding plenty of oxygen for the yeast. It also encourages aroma production and helps keep the fermentation proceeding without any off aromas.

Open containers also allow you to properly monitor the ongoing fermentation, chiefly by smell. At this stage your nose is the most important tool you have. Smell the fermentation deeply and regularly, checking for off aromas. If there are “off” aromas, stir or rack the must to oxygenate the must. Also add any un-added nutrients. If you have added your full dose of nutrient, then consider adding a small amount of DAP. This is one of the times I would use the unbalanced nitrogen in DAP.

Protect Aromas

I find frequent stirring, encourages stronger and more plentiful aromas. Stirring also protects the aromas by not allowing bad or stinky aromas to develop in the wine. I believe, it may also add a small amount of creaminess into the wine like a mini bâttonage. Bâttonage is a post-fermentation method of encouraging the yeast to add to the flavor of the wine, usually white wine, by frequent stirring of the finished yeast.

Also, consider at what temperature you would like to ferment the juice or must. Red grapes are often fermented at a warm to hot temperature to extract the most color and flavor from the skins. White aromatic wines will retain more of their aromas if fermented at a cool to cold temperature. Your choice of yeast is also important here, as you want a yeast that can handle either the hot or cold temperatures needed.

Finishing the Fermentation

After a week or more, the fermentation will finish up. The bubbling will slow and the yeast will start to settle to the bottom of the container. Check for sugar depletion by using a hydrometer. A refractometer will not be accurate where alcohol is  mixed in with sugar, nor will a hydrometer be fully accurate either. But you will know that the fermentation is finished when the hydrometer measuring bulb drops straight to the bottom of the measuring tube and is below 1 at .999. If you are close to these numbers, you can still finish the fermentation under airlock.

If the fermentation still shows some sugar, but looks like it has slowed or stopped, then you may have the beginnings of a stuck fermentation. This is another time I use DAP. Yeast find it more difficult to ferment any remaining sugar because of the higher alcohol content in the now new wine. Although the yeast makes the alcohol, they are not immune to its sterilizing effect. A small addition of DAP with a splash racking may give it extra energy to finish the fermentation. I don’t know why, but this is especially true when there is significant added sugar to fresh juice or juice that comes from a concentrate.

When your hydrometer confirms that all the sugar is gone from the juice, it is now wine. If you wish to add malolactic bacteria, a second malolactic fermentation (MLF) can occur. Do not add sulfate, and follow the procedure to revive the malolactic bacteria and add the specialized nutrition for MLF. The wine must be room temperature and any remaning sulfate below 10 PPM. Sulfate will hinder this fermentation.

When all fermentation is completed, the wine now can age. Sulfate is now strongly recommended to keep out unwanted spoilage microbes and prevent browning in white wine, and red for that matter. Fining for clarity or faults and final acid balancing can be performed.

Don’t be in a rush to remove the yeast from your carboys. The dead yeast can help clean up any faults and can add to the flavor through bâttonage. But unless stirred frequently, the yeast probably shouldn’t stay in the carboy through the lengthy aging process. It may harbor unwanted microbes. After a few months rack them off. And be sure to thank them for all their hard work!

The first step in making an excellent wine is a good, clean fermentation. Don’t let the yeast have too much candy, or sulk if they don’t feel loved and certainly don’t let them have strangers over to party in your wine. The secret to a good fermentation is that yeast just want to have fun!