What Causes Wine to Go Bad During Winemaking?

What Causes Wine to Go Bad During Winemaking?

What Causes Wine to Go Bad During Winemaking?

You've made your wine and it tastes like antifreeze (don't ask us how we know what that tastes like, the college years are a little blurry). What went wrong? You followed all the directions correctly, you included all the ingredients from the recipe, why does it taste so awful? Below are some of the possibilities. Don't be discouraged though. Keep your chin up and try again. That's part of the fun of making wine!

DEGASSING - Removal of residual carbon dioxide gas is very important. The failure to do this will result in the clarifying agent suspended or floating to the surface, thereby rendering it ineffective. The metabisulfite1 must be added prior to degassing to prevent oxidation2. Making your wine in a carboy3 will facilitate both mixing and degassing as it can be laid on its side and rolled vigorously.

STERILIZATION - Clean equipment is a necessity, and your siphon tubing should be food grade plastic. Also check for scratches or damage before each use. Periodically replace tubing.

SPLASHING - Another major cause of oxidation. Make sure that your siphon hose reaches the bottom of your container when racking or filling. (Always fill from the bottom up).

WOODY - Aroma of wood. Wood-aging wine for too long can also cause it to go bad.

SMELL/TASTE MOLDY - Negligence in upkeep of barrels or use of moldy corks can spoil your entire project.

STUCK FERMENTATION - The wine has stopped fermenting before reaching ~ 0.998 specific gravity4. This could be due to a number of reasons. In most cases you can restart it with a yeast starter as follows:

  • Pull approximately 1/2 gallon of your must5, add 1 packet of yeast energizer and 1 packet of Champagne yeast, mix and place in a warm area. Vigorous fermentation will occur in about 8 - 16 hours. Then you should add it to your original must.

RACKING - The operation of transferring a liquid from one container to another, leaving sediment behind. One of the main reasons for racking your wine is to get it off the lees6 or yeast sediment. This prevents the dreaded yeast taste in your wine.

SEDIMENT IN BOTTLES - If potassium sorbate is introduced to the must before fermentation is completed and a yeast cell has started to bud, it will not kill it but it will only slow down the completion of budding, which is the major cause of re-fermentation in the bottle. A wine hydrometer reading of the specific gravity at 0.998 will prevent this from happening.

CORKINESS - An unpleasant flavor and bouquet in a wine that was spoiled with a defective cork, the outside air was allowed to enter the bottle. Be sure to use a quality cork like Premium VS1.

SPECIFIC GRAVITY READING - The specific gravity reading at racking time will tell you if your wine is fermenting properly. This reading will tell you when the fermenting stage is complete and to proceed to the next step.

Specific gravity readings should always be taken at 15C and degassed to get a proper reading.

UNSANITARY EQUIPMENT - Equipment must be clean. The importance of this cannot be overemphasized. Vessels that have not been properly cleaned or rinsed could result in a soapy taste.


1. METABISULFITES: A Type of sulfite used in wine making. Sulfites occur naturally to some degree in all wines. In the winemaking process, sulfites are often added to cease fermentation, and can also be used as a preservative at many different points in the winemaking process. Sulfites prevent grape juice from being converted to vinegar and began getting an unfair reputation after laws in the late 1980's demanding winemakers to label all ingredients of their wine on the bottle, even those that were naturally occurring and not added to the wine.

2. OXIDATION: When exposed to air, wine is said to have undergone oxidation. This can compromise the taste of the wine. Avoid exposing wine to oxygen at all times. After opening a bottle, wine stoppers can be used to slow the oxidation rate.

3. CARBOY: A large rounded bottle, usually plastic or glass, which comes to a narrowed neck, often protected by a frame of some type. In winemaking, these are often used to contain the must during secondary fermentation. The thin neck makes it easier to pour the must with minimum oxidation, and the shape lends itself to being easily shaken.

4. SPECIFIC GRAVITY: the ratio of the density of a liquid, solid, or gas, compared to the density of a standard liquid, solid or gas. The standard for liquids and solids is water. Therefore, specific gravity in winemaking tells us how dense your must is compared to water.

5. MUST: the pressed juice used in winemaking before or during the process of fermentation. Typically, this is grape juice, but other fruits are used to make wine on occasion.

6. LEES: deposits of inactive, dead yeast or leftover yeast and residuals remaining after the fermentation and/or aging process.

Winemaking is not an easy hobby by any means, but enjoying the fruits of your labor is reward enough for most winemakers. Trial and error is the best method to perfect your own particular methods. Don't forget about winemaking etiquette! Share your wine with friends and family. Wine has been bringing people together for thousands and thousands of years. If someone gives you a bottle of their homemade wine, there are a number of unique wine gifts to show your appreciation. Wine charms, books, and wined themed candles are just a few fantastic gifts for wine lovers available right here on The Tipsy Grape.