# Spontaneous and Controlled Fermentation Tests in Industrial Table Olives Production
## 1 Introduction  
Olives, the fruits of _Olea europaea_ L. tree, have a high content of phenolic substances. These substances make them inedible due to the strong bitter taste. However, they become ready for consumption after an adequate transformation process. Once processed, table olives are widely used as appetizers or as an ingredient for culinary recipes. Table olives are the most well-known fermented food in the Mediterranean region, and their consumption is increasing year by year worldwide. However, despite their diffusion, production in certain cases is still craft-based [1, 2, 3].  
The debitering processes applied to table olives are many and different, and each has its own peculiarities aimed at obtaining a highly palatable and appreciated product, consumption of which is spreading throughout the world thanks to the popularity of the\"Mediterranean Diet\". The most common methods of debittering are the \"Castelvetrano\" and the \"Sevillan\" styles, which use NaOH for total or partial hydrolysis of phenolic substances, and the \"Greek/natural\" style, which uses epicarp resident microflora for phenol hydrolysis. [1,4]. Among the different debittering methods, the one that most attracts research is the \"natural\" method, as it enriches the sensory characteristics of the original fruit. This method involves immersion in NaCl brine after harvesting, during which time the olives begin a fermentation as a result of the spontaneous resident microflora of the epicarp. The fermentation usually lasts for several months (about 7 to 8, or even more) [1,5,6]. These microorganisms debitter the olives by hydrolysing the complex phenols glucosides responsible for the bitter taste (mainly Oleuropein and Ligtsroside) into simple phenols (mainly Hydroxyrosol and Tyrosol). In doing so, they enrich the product with aromatic substances [7,8]. This fermentation process is also affected by the concentration of NaCl in brine, and by pH, acid concentration, temperature, and other factors that can affect positively or negatively affect the process [9]. Moreover, the diversity of microbial and fungal species on the epicarp means that \"natural\" fermentations are never identical and, therefore, this method of preparation still represents a source of uncertainty regarding the characteristics of the finished product [3]. Over the years, several \"lab-scale\" experimental tests have been successfully carried out with starter cultures of selected microorganisms [10,11,12,13,14,15,16]. However, after review of the literature, there is little evidence of data obtained at an industrial level. We decided to perform tests on large quantities and under the same operating conditions as commercial/industrial processes in order to monitor the progress of the spontaneous fermentation from a chemical-physical and microbiological point of view inside an industrial facility and to verify the effectiveness of some starters in a guided fermentation.  
The choice to carry out \"field\" tests was dictated by the need to understand the processes that are commonly carried out by commercial producers and then to monitor the progress of the various components characterizing the evolution of the product. In this way, we aim to help companies obtain a product with constant and reproducible chemical-physical and sensory characteristics and to prevent the onset of anomalous fermentations.