Drying in food and non-food agro-industrial products is a unitary operation of great importance both at a business level and at an academic and research level, since the sectors of application are quite broad, such as fruit, flowers, grains, meat, dairy, spices, and dyes. It is also an operation before many size reduction operations, increasing the useful life of the products by eliminating the highest available water content and therefore reducing costs in product transportation freight. Among various types of drying such as microwave, hot air, and some hybrid systems (Cuccurullo et al., 2019), drying by forced convection is the most used in this unitary operation due to the benefits of cost and time drying, but despite the abovementioned, the affectations on the nutritional and organoleptic characteristics to which the products are submitted are quite high, which have taken to the innovation in other more efficient techniques and conserve better the nutritional and organoleptic characteristics of these products. Among the most efficient techniques are freeze drying (FD), far-infrared radiation drying (FIRD), heat pump drying (HPD), hot-air drying (HAD), and hot air combined instant controlled pressure drop drying (DIC). Some of these techniques have been well-studied, but other more emerging techniques such as far-infrared drying have not had as much theory published, so this article seeks to answer the following questions: Which raw materials are subjected to far-infrared drying? What are the mathematical models used in the application of far-infrared? To answer the two questions posed, this document consists of four phases. In the first phase, a theoretical framework is presented that relates the main concepts or definitions about the unitary operation of far-infrared drying. In the second phase, the methodology is explained with emphasis on the search equation used in Scopus. In the third phase, the results are explained in terms of countries of origin of publications, type of journal, time series of the articles and topics, raw materials evaluated in the articles, and the mathematical models. The last phase contains a discussion and an analysis of patents and contributions that will give answers to the questions raised as the main axis of this article.

Among the most important challenges at present worldwide is the conservation of food, mainly fruits, and vegetables, which a great loss occurs in the post-harvest process. One of the alternatives that offer better results in conservation is drying, one of the oldest techniques (Cheng et al., 2019), which is one of the methods that allow the separation of water from a solid (Ocon and Tojo, 1977) and consists of reducing the moisture content to a safe level where deterioration by microbial conditions can be significantly minimized (Cheng et al., 2019).

The drying is usually by evaporation in a gaseous stream, and the most commonly used gas for the drying application is air (Zartha and Palacio, 2011). This treatment can extend the shelf life of these products with great success (Wu et al., 2019), making them more acceptable for marketing or further use (Valiente and Tlacatzin, 1991). Currently, dry products are well-received by both consumers and transporters because the dry product facilitates transport and storage reducing costs (Wu et al., 2019). In the last decades, different drying techniques have been developed or implemented among which are HAD, FD, microwave drying, and infrared drying (Wu et al., 2019).

HAD is a process in which food is exposed to a flow of hot air. This process has no special requirements for expensive equipment and is commonly used because of its low process costs; however, this process has low energy utilization efficiency. Hot-air-dried products can reach a shelf life of ~1 year (Wang, 2019). But the long drying time causes a significant decrease in the quality of the final product (Zhao et al., 2019).

Freeze-dried food is considered the benchmark of high-quality dry products, which could preserve as much as possible several original properties of fresh materials such as appearance and nutrients (Zhao et al., 2019).

Microwave drying allows the food material to be placed in an electromagnetic field where, due to the friction and collision of the water particles, its temperature is increased and the process of water evaporation is accelerated (Wang, 2019). This method is compared to forced convection drying with hot air; microwave drying has a shorter drying time, has higher energy efficiency, and improves properties such as aroma, color, and rehydration, along with nutritional properties (Leanerts et al., 2018).

One of the drying methods that has gained great relevance in recent years at an industrial level is infrared drying, which years ago did not appear as an option for the industry, but due to the research on this type of drying that has been carried out and the advantages it has over other drying methods, it has begun to be implemented.

Infrared drying is based on electromagnetic radiation. Compared to other drying media, especially HAD, infrared produces savings in energy consumption, which is an important step toward conserving available energy sources (EL-Mesery et al., 2019). In similar conditions, infrared drying has great advantages over traditional air drying. Studies have shown that infrared has an effective moisture diffusivity and a higher thermal sensitivity than air drying (Wu et al., 2019).

In the industry, there are three types of infrared drying (far-, near-, and medium-infrared drying), of which the most emerging has been the far-infrared drying. This can be widely implemented in the food industry, as it can be used to dry a wide variety of agricultural products. This type of drying has several advantages if compared to traditional drying, ranging from efficient heating of products and excellent energy efficiency to a high quality of dry products because this type of drying does not allow the organoleptic and chemical characteristics of the products to be lost.

Several studies determined that drying of agricultural material through far-infrared is one of the most efficient, since the heating that takes place in it manages to promote the rate of dehydration of the products and also helps to improve the quality of these. This type of drying is very versatile, since it can be used alone or as a complement to other operations (Liu et al., 2019).

Infrared drying is quite practical due to its uniform heat distribution, fast drying speed, and simplicity of the equipment. Among the infrared technologies, FIRD was found to be more suitable for food processing, as most food components could absorb radioactive energy in the far-infrared region (Zhao et al., 2019).

Infrared radiation has become an alternative technique for food drying because the equipment required for this process is versatile and simple, which allows faster heating and therefore reduces drying times. Infrared drying works when the infrared radiation penetrates the material, and it is converted into heat energy and thus removes water more evenly. Infrared drying allows a more uniform distribution of heat than convection drying, and therefore, a higher-quality product is obtained (Rashid et al., 2019).

To obtain good results in the reading, the work was divided into four stages as follows:

These stages can also be seen in Figure 1.

To achieve a good analysis, first, the information found in the articles was organized, and to determine better results, graphs were created representing the results obtained. The graphs were created with the information of the countries that made the publications, the magazines in charge of publishing the articles, the main keywords found in each article, the most used technologies, and the products to which they are applied in that technology. Also, to determine the level of impact of the journals in which the articles were published, with the quartile in which each journal is located, a graph was made. It should be noted that there are four quartiles (Q1, Q2, Q3, and Q4) for the most important journals, in which the journals located in Q1 are those that have the greatest impact. The results obtained can be seen in Figures 2–6 and Table 1.

In Figure 2, the characterization of the technologies related to the unitary drying operation found in the articles evaluated can be seen, which amounts to 10 technologies, in which infrared drying is identified as the technology with the highest number of articles that refer to it, being ~28 articles, while the technology that appears in the lowest number of articles is drying by visible spectroscopy mentioned in two articles. But in this case, although the infrared drying is the most studied, it is not emerging. There are reports of its application from more than 10 years ago, which is why it is discarded, and far-infrared drying is selected, which was studied in five articles of the year 2019 and 2020, which shows that it is an emerging technology that brings multiple positive effects in the drying of agro-industrial products, leaving it in an advantage over the other technologies.

After knowing the different technologies, the products worked in all the articles were identified, and Table 1 is created in which the author, the product that this author investigated, and the purpose of this investigation are shown. This table is made to extend a little more information about the products and the purpose of these for each author, besides that it is possible to understand more widely the discussion that is later on.

Taking into account that the drying process is a very important operation for the conservation of food and the quality of the final product, which leads to innovate in new drying processes or evaluate the different technologies that exist to determine which is the most appropriate, taking into account the type of product and the process to which it will be submitted after the drying to ensure the higher performance of the product and longer duration, that is why in Figure 3, we can see which are the countries that have most evaluated the drying technologies applied to raw materials, China being the country with the highest percentage of publications of articles with 34%, followed by Iran, which had a participation of 11%, and the United States, with 8% of publications. We can also find to Colombia with a participation of 2% and 19 other countries that made publications of the drying technologies.

Figure 4 shows a compilation of the journals publishing the articles studied, in which 21 journals are reported, among which food science and technology, food process engineering, and food chemistry present the three first places concerning a greater number of publications of articles with a percentage of publications of 11, 7, and 6, respectively.

Keywords are an important part of an article, since just by reading them, we can deduce the subject of the article as well as make it easier to find the articles in the databases. For this reason, Figure 5 shows a compilation of keywords of the articles evaluated, giving a total of 18 keywords being infrared drying, drying, and infrared radiation Surface, the frequent keywords, participating in 14, 11, and 10 articles respectively.

In Figure 6, we can see the classification of the quartile of the magazines that published the articles of the drying technologies. This allows us to evaluate the importance of the magazines within their area, which is divided into four quartiles, classified from highest impact to lowest impact (Cheng et al., 2019), with those in Q1 having the greatest impact on the scientific community. In this case, we have 70% of journals in Q1, 25% in Q2, and finally 5% in Q3.

Journals that publish scholarly articles have a different focus each, although they may be in the same area each focusing on something different, some may generalize the topic while others zoom in and reduce the information further, making it more accurate and focused on some specific topics. In the research, in general, it was found that all the magazines talk, mostly, about topics focused on food, technologies, innovation, engineering, and research.

The journal in which more publications were found in the “food science and technology” followed by the “food process engineering,” both journals focused on a food field, one in science and technology and the other in engineering processes. These journals seek to publish progress on these issues, and to determine the progress, the best option is to compare it with what already exists or with other techniques to determine which is the most effective, and this is as several authors express it, as Carvalho et al. (2019); Wang (2019); and Fu et al. (2019), among others who made comparisons between different methods of drying and comparison between the product by applying the treatment and without applying it.

This is what these journals are looking for—to publish the improvements that have been found by different researchers worldwide, to improve access to information, and to generate benefits for the readers who are carrying out their research. The journals also have an impact level that is determined by the quartile SCImago in which it is located, the quartile what it looks for is to locate the publication in a journal according to its level of importance and impact, achieving this way that the publications are ordered so that the readers can facilitate their search of information (COLCIENCIAS, 2018), taking into account the previous thing and that the quartiles are Q1, Q2, Q3, and Q4, where Q1 is composed of the journals with the greatest impact, the current review is based on 70% of publications in Q1 journals, which suggests that the articles used for the study have a great impact among readers of research-related topics.

The research focused on the reading of publications on drying especially with the infrared technique, that is why in the search of keywords exposed by the authors of the publications, the main ones that are found are “infrared drying,” “drying,” “infrared radiation surface,” and some of the different products that are applied to the drying. The keywords are important because they allow the reader to identify which is the central topic of the article you are reading. This is why if the research was based on the search for infrared drying information, the most keywords found were related to these topics. Some of the authors who mention the most repeated keywords in the articles are Rashid et al. (2019), Daniel and Onwude (2019), Khampakool et al. (2019), and Borda-Yepes et al. (2019), among others.

They in their publications gave reason for the advances they have achieved with this drying technique compared to other techniques and with the improvement in the retention of the nutritional compounds of the products. Based on the above, it was possible to identify more easily the issues related to the research.

It was possible to identify drying as one of the most useful techniques for food preservation and that infrared drying was entering as a promising emerging technique for this treatment, and effectively, as expressed by the different authors, it was possible to identify what the drying process consisted of and how infrared is a technique that is well-implemented and with the respective adjustments can be effective in preserving fruit or food.

Drying is an operation that not only allows us to remove moisture from a product but also helps to make studies on the properties of these easier. In addition to combining new techniques such as far-infrared radiation, traditional drying methods better preserved the characteristics of these products.

Far-infrared drying aims to be one of the most widely used drying techniques in the future due to the benefits it brings such as low energy consumption and other features such as sensory quality, rehydration ability, and high nutrient retention that it provides to the final product.

Over time, the most effective way of preserving food has been studied, starting with sun drying and evolving into much more sophisticated techniques where the control of multiple variables is fundamental to guarantee the integral preservation of products—both their physicochemical and their organoleptic properties. This review of these technologies allows us to identify far-infrared drying as a very efficient drying technique that allows the dehydration of agro-industrial products with less physical–chemical impact.

A common factor that could be found from the articles was the application of this infrared drying technique in fruits and vegetables with high water content, such as kiwi, chives, and mushroom varieties. These articles based their studies on optimizing the technique by varying drying times, temperatures, pressures, even sometimes combining different drying techniques—all to preserve the organoleptic characteristics of the product, avoiding damage to thermolabile compounds and obtaining a dry food of very good quality, performance, and characteristics.

Drying is an operation that has accompanied human beings from their beginnings. This one is in almost all the industries, from the nourishing industry, for the elaboration of kinds of milk, in the dust, coffee, sugar, or dry fruits, until the no nourishing industry like the chemistry, this is an operation like the man has come evolving with time, obtaining several advances, like more optimal equipment to dry certain products, with more capacity and less power expense or equipment that maintains all the characteristics of the product that one of the most important factors today at the time of carrying out the drying process.

The articles presented in the paper are recent in 2019 and 2020 and give a basis for two things: a comparison is being made between traditional drying techniques, exposed by different authors, and a modern technique, exposed by the authors of recent studies on drying, and in turn that the information found, mainly on quality, is very current, being important to bring the technique to the practical exercise.

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.