Fermentation is one of the oldest forms of food preservation. This technique requires little energy and can improve the nutritional qualities of the product. The fermentation process can also facilitate the digestion of the food.
Som literally means acid in Laotian. In this section, we are interested in the fermentation process which converts sugars into acids by the intervention of lactic acid bacteria: lacto fermentation. It is customary to add rice to the preparation to increase the amount of sugar needed for the fermentation.
Lactic acid bacteria are naturally found in food and are microaerophilic i.e. they require little oxygen for their metabolic activity. The transformation reaction of sugars into acids takes place without the addition of oxygen, sometimes with the release of carbon dioxide and the production of other organic acids. The preparations are either firmly packed or immersed in a liquid and usually stored in an airtight container away from light. The limited amount of oxygen and light avoids the alteration of the color and consistency of the food.
The production of acid lowers the pH level and inhibits the development of microorganisms responsible for the putrefaction process. Some bacteria can be highly pathogenic. Among the most dangerous, we can mention Clostridium botulinum, a botulism agent. Most preparations are considered to no longer contain unwanted bacteria if their pH level is lower than 4.6 (ref Battock and Wong). Salt also favors lactic acid bacteria to the detriment of others. To limit the risk of contamination, we advise you to work with very clean utensils and to wear gloves. Make sure to use fresh, good quality, well-washed ingredients.
The final product will tell you if the fermentation is successful. The preparation must be free from mold and foul odors, such as ammonia. It must have a pleasant and tangy taste.
Som is a side dish. The recipes are calibrated to cook small portions. The fermentation time is given as an indication. The level of acidity will depend on the temperature of the room. Once the desired acidity has been reached, the preparation can generally be kept for a few days in the refrigerator. The cold slows down the fermentation without stopping it.
For lovers of the umami taste, we recommend adding glutamate just before serving, i.e. after fermentation.