1. Introduction

Louis Pasteur discussed the issue of fermentation [1,2]. He obviously suspected—and, in some cases, he knew—that fermentative processes are diverse and complicated. Indeed, although modern science recognizes more than one type of fermentation, a general definition should define fermentation as a biochemical process through which most microorganisms decompose carbohydrates to produce energy under anaerobic conditions [3,4,5]. According to Pasteur, “Fermentation is life in the absence of oxygen” [1]. In this somewhat obscure and phenomenological term, various types of fermentation are included, such as yeast fermentation, lactic acid fermentation, butyric acid fermentation, propionic acid fermentation and acetic acid fermentation. The diversity of the phenomenon leads to a variety of end products, which include CO_2, ethanol, organic acids and other organic molecules. It is many of these products that make fermentation so useful and interesting both to science and industry [3,4,5,6,7].

The process of carbohydrate decomposition creates a flow of protons and electrons. In aerobic conditions, the final receptor is oxygen (respiration), andin anaerobic conditions, the final receptors are other organic molecules, such as pyruvate or acetyl CoA (fermentation). Fermentation yields much less energy than respiration. The progressive oxidation of sugars involves the transfer of hydrogen ions from intermediate products in the pathway to the final receptor. The Embden–Meyerhof–Parnas pathway (EMP) is utilized in most cases to decompose glucose to pyruvate (homofermentive strains). The Entner–Doudoroff pathway decomposes lactose molecules, while the heterofermentive strains decompose pentoses and other sugars through the phosphoacetylase pathway. The end products depend on the substrate as well as the microorganism species and strain (Figure 1 and Table 1). Different species and different genera have different capacities of fermentation [3,6,7]. For example, E. coli has limited fermentation capacities regarding the variety of end products as compared to lactic acid bacteria (LAB). On the other hand, beneficial fermentation properties can be engineered. By inserting a lactic acid dehydrogenase gene from a bovine muscle, Saccharomyces cerevisiae can produce lactic acid in levels similar tothose of LAB [8].

Microorganisms and carbohydrates are abundant in nature and fermentation occurs in every anaerobic environment. It follows that it is not a question of “if’ but a question of “when” and “how” early humans discovered and harvested the benefits of fermentations in the domain of food and beverage. Near Lake Neuchatel in Switzerland, archaeologists discovered the remains of cheese manufacturing from 6000 BCE [9]. Homer refers to Cyclops Polyphemus as a cheese producer, while in many cultures, such as the Mongols, the Tuareg, the Bedouin, the Tibetans many central Africa tribes and Amazon natives, among others, strong evidence exists of fermented curds production in the antiquity [10,11]. Bread is depicted in ancient Egypt scrolls aging from 2700–2500 BCE. In the third century CE, 72 kinds of bread were listed in Athens [11]. Finally, wine must have been “invented” somewhere between the Black Sea and the Caucasus mountains from 6000 to 3500 BCE. Apparently, someone accidentally left crashed grapes in a container and tasted them much later [12,13,14]. A similar theory is presented for beer brewery, but in this case, meshed cereals with water were left the container [15]. In ancient Egypt, the kneading and baking facilities were beside the beer breweries, obviously both using Saccharomyces cerevisiae [15,16].

This entry is adapted from the peer-reviewed paper 10.3390/foods10010069