Why my wine fermentation produces vinegar?

Oxygen is considered the principal enemy of wine fermentation process. Ethanol production by yeasts is carried out under anaerobic conditions in the presence of natural sugars such as glucose, sucrose and fructose; however if oxygen enters to the fermentation system, an oxidizing condition is generated. According to organic chemistry, ethanol is transformed in acetic acid following the reaction:

Ethanol + Oxygen (Air) => Acetic Acid

(C2H5OH) + O2 => CH3COOH

Acetic acid is undesirable byproduct due to its unpleasant smell as well as its repulsive taste.

In order to avoid the Acetic acid formation during the fermentation process an oxygen (or air) limiting is desirable. To do this, it is highly recommended the use of check valves in the gas exhaust of fementer, if it is not possible a simple silicone or plastic pipe immersed in water or lime solution is useful to control the inlet or air.

WINE MAKING STEPS No 2

Level II: Must preparation

The fruits are harvested both by hand and with motorized harvesters. However, harvesting by hand is more recommended. Avoid an exposure to air and temperatures up to 27 ºC.

A plastic material is recommended for fruit handle. Fermentation vessel should be made of plastic or glass too.

After harvest, fill the fermentation vessel with approximately 1/3 of fruit and complete the total volume with water and others additives such as sugar and organic acids for pH adjust.

Sugar concentration before fermentation should be 200 g per liter of must, however it is a free variable defined by the winemaker. A white sugar must be used for all winemade production. Remember: final colour is the key for a good selling and wine acceptance.

Some authors recommend the use of sulphites for oxygen control during anaerobic fermentation; however my experience in this field shows that sulphites could promote the wine degradation by the formation of sulphur compounds. So do not use them.

Yeast is rehydrated under warm water (28ºC) for 1 hour, prepare a stock solution of 1g yeast per liter and add a 10% of total must volume to the fermentation. For example if the most volume is 2000 mL a 200 mL of yeast solution is required.

Once you add the yeast solution to the must the fermentation has started.

Level III. The heavy machine … The Fermenter

Fermenter design has vital importance for winemaking process. All the fruit transformation occurs here and the success of final product is obtained here. Fermenter is practically a closed vessel, at the top is inserted a rubber pipe for gas exhaust (CO2), remember, in order to make your process safely is obligatory to control the vessel pressure. Really a fermenter is simple to design and build, plastic and glass materials are recommended.

Fermenter fill volume is normally 80% of total capacity.

It could be washed by using a diluted NaOH solution