Sunday, January 30, 2011

Part 1: Practical Chemistry for Natural Vinegar

Abe V Rotor

Vinegar (vin egar) means sour wine. In chemistry it really is. The general formula is, first, wine is produced, then vinegar, and lastly, nata de coco.

Sucrose/Glucose  Ethyl Alcohol  Acetic Acid Nata de Coco

Now let us substitute the three items.

Sugar/Fruit  Wine  Vinegar  Nata de Coco

We can see that vinegar is not a direct, but a secondary product of fermentation. Sugar is fermented into wine first, then the wine undergoes oxidation. In organic chemistry this is illustrated as follows:

Step 1- Fermentation

C6 H12 06  4C2 H5 OH + 2CO2
Cane/Fruit Sugar Zymase (Yeast) Ethanol or Wine Carbon Dioxide gas

Step 2 – Oxidation

C2 H5OH + O2  CH3COOH + H20
Ethanol or Wine Oxygen Acetobacter aceti Acetic Acid or Vinegar Water

This basic knowledge in chemistry is the key to the success in wine making as well as in vinegar manufacture. The first step (fermentation) will indicate that our culture is proceeding properly if wine odor is detected. At this point, we know that the sugar is being converted into ethanol or wine. We should not be bothered if we do not detect vinegar odor immediately.

In the second step, we detect both wine and vinegar odor several days from the start of fermentation. Why is this so? Because we allow the two processes – fermentation and oxidation – to take place simultaneously. As soon as sugar is converted into ethyl alcohol by yeast action (Saccharomyces), this product is immediately converted into acetic acid through oxidation and by the action of the vinegar bacteria complex (Acetobacter aceti).

Sukang Iloko

Sugarcane juice is placed in the jar and is allowed to ferment for a week. The local practice is that no commercial yeast is used because wild yeast is ubiquitous, which means that yeast cells are found everywhere – in the air, in the cane, flowers, ripe fruits, yellowing leaves, or carried by fruit flies (Drosophila).

Fruit flies are very small, hovering on overripe fruits. They carry yeast cells and other fermenting fungi and bacteria. The yeast cells initiate fermentation as they rapidly multiply in the first week. There are thousands in one milliliter of the fermenting material. It is also during this time that the production of ethyl alcohol reaches its peak of up to 13 percent by volume. This yeast population later drops, decimated by own product, ethanol,which is toxic to them. This can be explained by the principle of autotoxicity. Meanwhile, Acetobacter and other fermenters increase their own activities by taking the process of oxidation and acetification.

If oxidation of the alcohol is controlled during this time, the end product is wine. Since there is no antiseptic procedure followed in preventing oxidation, and entry and subsequent multiplication of Acetobacter complex causes the intermediate product to become a mixture of wine and vinegar. As oxidation and acetification (acetic acid or vinegar formation) continues. In another week or so, practically all the alcohol produced will become acetic acid.

After this, the young vinegar begins to age with time, the quality of natural vinegar improves. During aging process, the residual sugar undergoes a secondary fermentation by other fermenters, causing it to become acetic acid. Ageing, aside from making the vinegar mellow, increases its acidity. This is the opposite of “artificial” (glacial acetic acid) vinegar that is sold in markets cheaply.

Natural vinegar, other than sukang iloko, comes from nipa, coconut, cashew, pineapple, mango, banana, and chico. Basically, the process is the same.

Quality Determinants

The difference in taste and other qualities may be traced to the following factors:

1. Raw material (the source of sugar) used.
2. Amount of sugar in the material or substrate. Ten to 15 percent is preferred.
3. Availability and rate of yeast cell reproduction and other fermenters.
Commercial yeast is added for faster fermentation, while inoculation of vinegar mother liquor helps acetification.
4. Temperature and initial acidity or pH. (Raised temperature and acidity
enhance faster reaction).
5. Presence or absence of contaminants. Arrest bacterial decay which give a trace of rotting odor. Too much fleshy fruit and low sugar level in the substrate are often the cause of this problem.
6. Ageing time. This is from three to six months for commercial vinegar, one year for the premium.
7. “Green thumb” and sixth sense. (Skill and good management)


No comments: