Turning a juice into wine is a remarkably simple process. Just add some yeast to some juice and boom... wine. Just leave some fresh pressed juice sitting out too long, boom... wine. For the most part, juice wants to become wine. It is a part in the natural decomposition cycle. Where things get tricky is when you want to turn that juice into great wine.
As a beginner, it is tough to figure out what parts of the process are important and what are not. When a wine goes sideways, it is tricky to diagnose where things went wrong and usually "must not have cleaned the equipment good enough" is the go-to answer when in reality, this is rarely the case. Here are some common mistakes made by new winemakers that can result in a lower quality or outright bad wine.
1. Racking and Racking and Racking
A common misconception is that the secret of a crystal clear wine is to rack it as many times as humanly possible. I remember this advice when I first started, and probably racked that first wine four or five times for no good reason.
Racking is a relatively oxidative process. Each time you rack the wine, you are exposing the wine to oxygen that can react with the delicate fruit aromas and bind with the free SO2 that you have worked so hard to preserve. To maintain adequate SO2 levels and offset the oxygen exposure, camden tablets or potassium metabisulfite is added to replace the 15-20ppm of free SO2 that will bind in the process. With each racking and SO2 addition, the bound SO2 is increasing, further contributing to the loss of fruit and aroma in the wine.
A wine will clear up without repeated racking, and normally without the help of any fining agents. There are a few good reasons to rack, however. If a wine gets a little reductive just after fermentation (rotten egg/sulfur smell or musty), a little air can react with the hydrogen sulfide and resolve the problem. Another reason to rack is if the lees begin to pile up too high in the carboy. The lees contain fruit pulp, yeast cells, and the occasional spoilage bacteria. If the lees are 3/8 inch deep or less, there is no reason to rack off of them. If they become too deep, it is a good idea to rack off the lees to reduce the risk of spoilage or byproducts of stressed yeast cells. Another good reason to rack is to pull the wine off of the oak if it seems to be at a level that you are happy with.
The main take away though... don't rack if you don't need to. For more tips on when to rack, checkout this article.
2. Minimizing Oxygen Exposure Too Soon in the Process
A healthy fermentation needs a little oxygen to stay balanced. Yeast cells have two main modes of action when dealing with glucose; anaerobic and aerobic respiration.
The first mode, anaerobic respiration is alcoholic fermentation as we know it. The yeast cells take in sugar in the absence of oxygen and create CO2 and ethanol. This process is great, but does not allow the yeast to restore energy to stay healthy and can ultimately result in a stressed fermentation giving off stinky hydrogen sulfide.
The second mode is aerobic respiration, where yeast takes in glucose in the presence of oxygen and creates water and CO2. Aerobic respiration allows the yeast to restore energy and helps promote budding. This helps increase your yeast cell count and assures a nice youthful population of yeast.
You don't need to get crazy with the air exposure... just don't get crazy about preventing it at the stage of active fermentation. I usually ferment with a loose towel or sheet over the bucket or barrel and churn the wine up one to three times a day. Red wine naturally gets churned in the punch down process. Wines that are not fermented on the skins can also benefit greatly from a daily stir. To aid in churning up the wine or punching down, checkout these awesome tools.
3. NOT minimizing Oxygen Exposure Later in the Process
When the air loving and microbially competitive yeast are all but gone, it is time to start really being careful about oxygen exposure. Leaving a carboy partially full is a recipe for disaster, even if you do not ever remove the airlock. When the wine enters the aging period after primary fermentation it is important to top up to the neck of the carboy. A topped up wine has very little surface area and gas volume compared to the large volume of liquid, greatly reducing the speed that a wine can absorb oxygen.
Why is oxygen such a concern now? Unlike beer, wine is never sterilized completely. Aerobic bacteria like acetobacter are lying dormant, waiting for a little oxygen so they can get to work in converting your ethanol into pungent acetic acid, or nutty acetaldehyde which can later reduce into ethyl acetate having a distinct nail polish remover smell. To prevent this from happening, we need to create an unfriendly environment for these bacteria. The first step is to minimize oxygen contact as the wine enters aging, and the yeast are not there to grab up the oxygen molecules. Wines high in tannin, like skin fermented Cabernet Sauvignon will have naturally higher antioxidant properties but as time goes on, reactive tannin will bind up, and become less available to scavenge oxygen. Wines high in acid (Low pH) like a dry Riesling from the north are naturally a little more unfriendly to our unwanted bacteria but they are not invincible. To assure that the spoilage microorganisms cannot take hold, we need to maintain adequate free SO2 levels in addition to minimizing oxygen contact. Here you can learn a lot more about how to maintain free SO2 levels.
4. Confusing Potassium Sorbate with Potassium Metabisulfite
Potassium sorbate helps to stabilize a wine that is going to be bottled with residual sugar. Potassium metabisulfite is your source of Sulfur Dioxide (SO2) and is your main defense against spoilage microorganisms and oxidation but has little effect at deterring wine yeast.
In a wine kit, potassium sorbate and potassium metabisulfite come in little packets on top of the juice concentrate. The packets are nearly indistinguishable and the names are similar, making them easy to mix up.
It is common to add potassium metabisulfite (SO2) before fermentation to suppress bacteria (though this is not necessary in a kit wine). Wine yeast has a high tolerance to SO2, and can get a head start against other bacteria assuring that it dominates the fermentation. Once established, wine yeast creates ethanol and CO2, making it even more difficult for other bacteria to get off the ground.
Potassium sorbate coats the yeast cells, restricting the ability to bud and multiply. While this does not kill the yeast, it will severely stress the fermentation and make it extremely difficult to finish. Potassium sorbate should NEVER be added before fermentation but it seems to be a very common mix up. I get an email about once a month about the accidental addition of potassium sorbate pre-fermentation. With a massive yeast starter, you may be able to get through the fermentation in the presence of potassium sorbate but it will certainly be a struggle.
The ideal way to use potassium sorbate is to wait until the wine is crystal clear, indicating a very low yeast cell count. Rack the wine off of any lees, and mix in the potassium sorbate. Make sure the potassium sorbate is fresh and not from years past. Once added, you can back-sweeten the wine or bring a cold crashed (intentionally stalled) wine back up to temperature. Learn more about sweetening wine here.
5. Blaming Bad Wine on Cleanliness
The danger in blaming a bad wine on poor cleanliness, is that you are usually not getting to the root cause of the problem and are likely to repeat. Because wine is not sterilized and is fermented fresh off the vineyard, the bad bacteria that could cause problems are already there. No amount of cleaning of equipment will eliminate the bacteria from the juice or grapes.
Good winemaking is about learning how to best manage the bad bacteria. Early on, you may choose to sulfite with about 50ppm of free SO2 to hold back any unwanted microorganisms from the vineyard, the tractor, the crate, or the pickers hands. You may choose to feed the yeast with Fermaid K or Diammonium Phosphate (DAP) early and cut them off later in the fermentation to create a wine that is absent of nutrients for the little critters to feed on. Additionally, maintaining proper SO2 levels relative to the wines pH during aging will all but eliminate the risk of microbial spoilage. Smelling the wine daily during the active fermentation will help catch hydrogen sulfide or acetic acid before it becomes a problem. Selecting good healthy and properly ripened fruit can go a long ways in creating an excellent wine. Here are some common wine flaws and faults and their causes.
We have all probably made at least one of these mistakes but have hopefully learned from them and moved on. If you have any big mistakes that you have seen or done yourself, please mention in the comments!