**1. Introduction**

In ancient times, soap was produced with rancid oils and animal fat waste, involuntarily creating a circular economy with the requalification of products no longer used for human nutrition [1].

In recent times, the production of soaps, defined by law as cosmetic products, is regulated by the European Union [2]. The regulation determines and limits the substances to be used for the saponification processes (Regulation (EC) No. 1223/2009 article 14–17 [2]) and indirectly determines the chemical, physical, and mechanical treatments to obtain adequate raw materials for the cosmetic sector. Exhausted oils and fats, dangerous for human nutrition, are necessarily treated to eliminate all toxic and dangerous components such as heavy metals, microplastics, peroxides, alkyl esters, and suspended particles [3,4].

Companies that produce soaps buy large quantities of regenerated oils and fats, adding chemical compounds such as surfactants, parabens, silicones, and sulphates. These companies contribute to the recycling of regenerated oils and fats but add pollutants to improve certain products' characteristics [5,6].

Often, artisanal companies use edible oils, such as olive oil, for obtaining natural and high-quality products. These soaps are obtained from food and not from food waste [7–9].

**Citation:** Ferracane, A.; Tropea, A.; Salafia, F. Production and Maturation of Soaps with Non-Edible Fermented Olive Oil and Comparison with Classic Olive Oil Soaps. *Fermentation* **2021**, *7*, 245. https://doi.org/ 10.3390/fermentation7040245

Academic Editor: Diomi Mamma

Received: 30 September 2021 Accepted: 27 October 2021 Published: 29 October 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Scientific studies report the recycling of olive production waste, such as vegetation water, pomace, and plant parts of the tree, but there are relatively few studies in the literature on the recycling of damaged and overripe non-edible olives [10–13].

The authors were focused on the use of non-edible drupes (food waste) for the production of high-quality soaps through natural fermentation processes.

Non-edible olives are drupes with defects that develop negative and irreversible chemical, physical, and organoleptic alterations. Producers of fine oils eliminate these olives to obtain an excellent quality of the final product oils [14]. Furthermore, these drupes cannot be marketed because they do not have the minimum requirements defined by the European Community [15].

Non-edible olives are therefore used as fodder, natural fertilizer, and for the production of energy biomass [11,13].

The aim of this study was to produce and evaluate the different ripening stages of soaps produced with non-edible fermented olive oil (NEFOO soap) considering three parameters: pH, color, and solubility. The results obtained were compared with those obtained from soaps produced with extra virgin olive oil (EVOO soap).
