The multiplicity of halal standards: a case study of application to slaughterhouses

Food products suitable for Muslim consumers should be halal certified, particularly when their origins or production processes are doubtful. However, there is a multiplicity of halal standards. This situation may generate confusion, particularly for producers in Western countries who would like to certify their products in order to export them to Islamic countries. This study analyzed the reasons underlying the multiplicity of standards and reviewed the attempts of harmonization over time. Then, the case study of application to slaughterhouses was considered, by comparing four different halal standards (namely GSO 993:2015, OIC/SMIIC 1:2019, HAS 23103:2012, and MS 1500: 2019) representative of different geographic areas. Animal stunning was critically examined, comparing tradition with modernity. The study evidenced that the basic requirements related to slaughtering are common to all the halal standards considered, but several differences occur in more specific details. Only a close collaboration between the authorities of all the countries involved in issuing halal certifications will lead to a homogeneous regulatory framework with unified certification and accreditation procedures, increasingly required in a globalized market.


Introduction
Religions and customary beliefs contribute to, and strongly influence, food habits, particularly through food laws imposing or prohibiting the consumption of certain food products. Religion is therefore a fundamental component of the dietary culture that communities develop as it typically symbolizes its heritage and the sociocultural aspects of its ethnicity [1]. Islam is no exception to this, only permitting for the consumption of clean, safe, and fully lawful food and beverages that adhere to Islamic rules. Such food and beverages are named halal, which is the Arabic word for "lawful", "permissible", "approved", and "legal", with the opposite being haram, which means "forbidden".
With 1.8 billion Muslim consumers worldwide [2], the global Muslim spend on food and beverages accounted for $1.4 trillion in 2018 and is expected to reach $2.0 trillion by 2024. According to the 2019/2020 Report on the State of the Global Islamic Economy (SGIE), the 57 countries of the Organisation of Islamic Cooperation (OIC) imported $184 billion in halal food and beverages, with intra-OIC trade accounting for $34 billion [2].
Muslim awareness for halal products has increased in recent years. According to a survey carried out in 2016, 96% of Muslim travelers considered halal food to be critical, 85% rated halal food at the facility around them as important, and 81% rated having no alcoholic drinks at restaurants/food outlets as important [3]. This high level of awareness is due to the availability of apps which link consumers to halal products/restaurants, as well as to the development of halal hubs [2]. Moreover, the halal market is not constrained to Muslim countries alone: the highest halal food expenditure per capita is in European and North American Muslim minority countries [4]. Therefore, the halal markets of Western countries are also worthy of attention.
Food products suitable for Muslim consumers should be halal certified, particularly when their origins or production processes are doubtful. However, there is a multiplicity of halal standards. While standardization would seem to suggest regularity and homogeneity, with a reduction in diversity, a multiplicity in the world of standards has emerged with globalization [5], particularly for those standards that have a strong cultural and geographical basis linked to ethno-religious factors, such as halal. This situation may generate confusion, particularly for producers in Western countries who would like to certify their products as halal in order to be able to export them to Islamic countries.
Therefore, this research aimed at (i) reviewing the basic principles on how food technologists certify food products or raw materials as halal, (ii) analyzing the attempts of halal standard harmonization over time, and (iii) comparing the application of four different halal standards established in different geographical areas. The case study of slaughterhouses was considered, with critical considerations on animal stunning between tradition and modernity.

Sources for halal precepts and schools of Islamic thought
The primary sources for halal precepts are the Quran and the Sunnah of the Prophet (the traditions of the Prophet, set forth in the hadith) but, with the evolution of legislation in Islamic history, secondary sources have been added over time. Indeed, when the primary source does not provide an adequate answer to the question, Islamic judges along with religious scholars (ulama) intervene to solve the issue in three different ways: (i) by looking at similar situations or principles (qiyas, i.e., reasoning by analogy), (ii) by independent critical reasoning (ijtihád), and (iii) by consensus of commentators on a controversial point of the law (ijmá) [6,7].
By the end of the 11th century, Muslim scholars were focused on developing thorough methodologies in order to clarify and understand every aspect of the Islamic law, the shari'ah, composed of the sum of laws, orders, faith, and acts given to mankind via the Prophet. Later, these methodologies became known as "school of Islamic thought" (mazahb or madhab) within the Muslim jurisprudence (fiqh) [8]. A wide cultural variation in early Muslim jurisprudence occurred, but four jurists of Sunni Islam emerged: Abu Hanifa al-No'man bin Thabit, Abu 'Abd-Allah Malik bin Anas, Mohammad ibn Idris al-Shafi'i, and Ahmad bin Hanbal. Named after their leading interpreter, four juridical schools were established: Hanafi, Maliki, Shafi'i, and Hanbali, with a different geographical distribution [9,10]. The followers of the Hanafi school are mostly prominent in Turkey, Pakistan, Afghanistan, Muslim region of China, and states of the former Soviet Union; the Maliki school is concentrated in North Africa, northern Nigeria, and Arabian Gulf States; followers of the Shafi'i school are found in Palestine, Lebanon, part of Egypt, Iraq, Yemen, Malaysia, and Indonesia; the Hanbali school has most of its followers in Saudi Arabia [10]. In the Shia branch of Islam, meanwhile, other schools of law were established, such as Ismaaili, Jaafari, and Zaaidi, but they are much less represented than the Sunni schools [11].

Halal precepts in the food sector
For non-Muslims, the word halal is usually associated with the food that Muslims are allowed to eat. The halal precepts related to food are defined in the Quran verses 2:168, 2:172, and 2:173.
Food hygiene measures vary from one country to another, and also depend on the availability of resources; the situation was more difficult in the past, but food hygiene standards are still low today in some areas of the world. Dietary prohibitions dictated by religious laws helped to reduce mortality rates and to limit the spread of endemic diseases in various populations. The halal precepts concerning food predominantly focus on the following issues: ban on toxic substances and blood, slaughter methods, and permitted and prohibited animals. Therefore, the term halal was primarily linked to meat, but starting from the 1990s, the application of halal principles has been set out in greater detail, covering 6 different food categories (Table 1) [12]. In 1997, the FAO and the WHO drafted general guidelines for the use of the term halal, recognizing halal food in a broader sense than related only to meat [13].
Muslims are prohibited to consume alcohol, as indicted clearly in the Quran surah 5:90. Alcohol in halal food refers to ethanol: therefore, all fermented or distilled alcoholic drinks, which alter the consciousness, are forbidden. Many halal standards allow alcohol if its concentration in the finished product is less than 0.1%, when the source of alcohol is not from khamr (fermented or distilled beverage) [14]. An interesting case is vinegar. Despite deriving from wine, which is haram, vinegar is halal because alcohol is converted to acetic acid. This chemical conversion, which removes the impure nature of a forbidden substance by producing a different one, is named istihala [14].
Regarding the permitted and prohibited animals, the meat of domesticated animals with split hooves, such as goats, camels, buffaloes, sheep and cattle, is allowed. From the bird category, chicken, ducks, turkeys, pigeons, and sparrows are all allowed. In contrast, the meat of swine (Quran, 6: 121), boars, and carnivorous animals including birds of prey (eagles, ospreys, and falcons) is prohibited, for "the eating of all fanged beasts of prey, and all the birds having talons" is forbidden (Sahih Muslim, 821-875 AD) [15]. All Muslims can eat fish with scales. Some groups do not accept fish without scales such as catfish [16]. There are significant differences when it comes to seafood such as mollusks and crustaceans, depending on the religious school [14]. Animals that live both on land and water such as crocodiles, seals, and frogs are all forbidden.
As for the slaughter, the Islamic shari'ah defines the specific conditions for the prescribed method of ritual slaughtering (described in detail later in this review), named dhabiḥah or zabiha, which means "slaughtered animal". To meet the halal requirements, meat has to derive from the permitted animal species, and must be slaughtered by a Muslim, nominating Allah's name while slaughtering (Quran, 6: 118). The neck has to be cut by a sharp knife, to allow for the rapid and full draining of blood, while ensuring the quickest possible death of the animal.
There are three methods of slaughtering according to Muslim jurisprudence (fiqh). The first is al-Zabh, which is for domestic animals such as cows, sheep, chickens, geese, and ducks. The second is al-Nahr, for longnecked animals, such as camels and horses, cutting the throat between the start of the neck and the chest. The third is al-Aqr, causing a wound by an arrow or sharp tool in any part of the body of a wild animal which is out of control or animals that fall in a well [17].
According to the Hanafi school, slaughtering must be carried out by a sharp knife from the front of the neck by cutting the trachea (halqum), the esophagus (marii), and both the carotid arteries and jugular veins (wadajain), or at least one of the jugulars. According to the Maliki school, the trachea and both the carotid arteries and jugular veins must all be cut, while cutting the esophagus is not essential.
For Shafi'i and Hanbali, meanwhile, cutting the trachea and the esophagus is required, without specifying anything about the carotids and jugulars (whose cut is recommended according to Sunnah). Cutting the head of the animal is disliked (makrooh) [17].
Muslims are also prohibited from consuming blood (Quran 6: 121). Ingredients and additives derived from blood, such as albumin, are haram. A combination of prohibited ingredients (pork and blood) occurs in some traditional food products where pig blood is the main ingredient, such as the Italian dessert known as "sanguinaccio" [18], "black pudding" in the UK and Ireland, and the Vietnamese dish known as "tiet canh".

Halal certification procedure
Halal food is produced according to Islamic law but should also comply with Hazard Analysis Critical Control Points (HACCP) and Good Manufacturing practices (GMP). The certification body must have the technical competence to assure that religious requirements and food safety standards are both met. Any food product can be subjected to halal certification, including processing aids. For example, activated carbon, used in the food industry as a clarifying agent [19], has a source that is not exclusively vegetable-based, which means that it is not always halal: therefore, the certifier must be an expert in the field of food technology in order to undergo a correct halal compliance check.
The key point in certifying a food product is to ensure its suitability for the selected halal standard, by following a conceptual model that can be defined as "Source-Composition-Manufacturing" (SCM), shown in Fig. 1. According to this model, the main food source has to be clearly identified in order to verify whether it is vegetable, animal, microbial, chemical, synthetic or biotechnological [14]. Then, the composition has to be considered to verify if each critical ingredient, additive, adjuvant, or processing aid, holds a halal certification. For the non-critical ingredients, a halal statement filled out by the supplier/producer is sufficient, as illustrated in Fig. 2 for the cheese industry for example. Lastly, the manufacturing facilities have to be inspected to assess if the production lines are solely dedicated to halal products or if their use is shared with non-certified ones. In the latter case, the criticality of the non-certified food products for which the line is used must also be checked. For example, being produced exclusively by mechanical means, without any chemical intervention, nor the addition of processing aids or preservatives, extra virgin olive oil (EVOO) can be considered "naturally halal" [4]. EVOO is, therefore, a product without criticalities, and the production line does not need to be sanitized in a halal specific way during the production of EVOO.
The previous concepts can also be applied to rennet, used in the dairy industry for enzymatic coagulation of milk. Coagulation is a processing phase associated with a halal critical control point (halal CCP) (Fig. 2). Rennet, in fact, is generally obtained from a young animal's stomach (usually a calf) or, alternatively, from a microbial source [14,20]. In order to certify the halal suitability of rennet, the food technologist has to check its source. This criticality remains high because porcine rennet was used in some cheeses in the past, and is still used today in the production of the Italian "Pecorino di Farindola" [21]. Besides, even if the source is a permitted animal, it must be halal slaughtered to be acceptable. Meanwhile, if rennet comes from a microbial source, produced through the transcription of bovine chymosin genes [22], the halal certifier should check the substrate used for microbial growth, as it may contain proteins or other materials of animal origin. The substrate also has to be checked for the commercial starters used for fermentation (halal CCP). Therefore, fermentation is another processing phase associated with a halal CCP, and initial commercial producers must be halal certified (Fig. 2).
Furthermore, rennet composition has to be accurately checked to verify the conformity of all additives and adjuvants used to produce it. Chemicals might be used to release enzymes from tissues: such chemicals have to be halal approved. Some additives might be used for the Fig. 1 Diagrammatic representation for the source-composition-manufacturing (SCM) conceptual model, used to assess the conformity of a food product to halal standards. The first step consists in identifying the main source of the food product: vegetable, animal, microbial, chemical synthetic, or biotechnological. The second step consists in checking the composition, to classify ingredients, additives, adjuvants, and processing aids as critical and non-critical for the halal status. The third step consists in inspecting the manufacturing facilities to assess if the production lines are solely dedicated to halal food products or their use is shared with non-certified ones. In the latter case, the production line has to be sanitized before the halal production standardization of rennet, such as emulsifiers and preservatives, in order to increase its shelf life. These additives too must be halal [14]. A similar situation occurs for lipase and colorants used for some cheeses, which again must be halal certified. Salts and acids, however, are not in any way linked to animal sources; therefore, a halal statement is sufficient.
As for the production lines (i.e., the "manufacturing" step of the SCM conceptual model), they must be halal and thoroughly cleaned, for generally speaking, the manufacturers of animal enzymes keep various animal sources on their premises. Therefore, a halal-approved cleaning procedure is required to avoid any risk of cross-contamination. It is also important to check that the first production site of the food product, has been halal certified. When food companies buy the product in bulk and just pack it, then, the halal audit must also be performed where the production takes place, i.e., the producer should be subject to checks, as well as the packing company. The food technologist should also determine the final use of an ingredient, defining whether it is intended for direct consumption or not, whether it is a semi-finished or finished product, in order to determine the technical documents necessary to ensure compliance with halal requirements.

Halal standards in different geographic areas
Over time, and spreading far and wide from its initial center of origin, several different traditions have emerged within Islam which, while maintaining the unity of believers, at the same time caused a certain diversification. The spread of Islam was accompanied by a cultural transfer from the areas of origin, but met with the juxtaposition of local culture, which led to distinctive characteristics [23].
In Southeastern Asia, the presence of Islam was recorded as early as the seventh century A.D., with a more significant spread starting from the end of the thirteenth century [23,24]. There are also sources of evidence that point toan Arabic origin, though via the Persian and Indian coasts, thanks to feasible sea routes. Indeed, maritime trading links existed between Southeastern Asia and Southern India, where there was a significant Muslim presence [24].
Southeastern Asian countries, such as Malaysia and Indonesia, with large but not exclusive Muslim populations, were the first to develop halal standards and certification procedures, in order to ensure that the Muslim consumers would trust and accept food produced in these countries by non-Muslim manufacturers [4]. the halal certification process of cheese, according to the criticality of ingredients/additives/adjuvants. Fermentation and enzymatic coagulation both represent a halal critical control point (halal CCP) because these processing steps involve the use of ingredients or adjuvants that are considered critical for the halal status. All the ingredients, additives and adjuvants required at each processing step have to be accompanied by a halal certificate, if they are critical (such as commercial microbial starters, rennet, colorants and lipase) or simply by a halal statement if they are not critical (such as acids and salts) Nowadays, the Muslim population in Malaysia is around 61% [25], and around 87% in Indonesia [26]. With much of the food produced by the non-Muslim Chinese community, the need for halal verification was of paramount importance in these countries. The establishment of halal standards was therefore promoted by the government to guarantee manufacturers' compliance with halal rules.
In the areas where Islam originated, meanwhile, the almost entirely Muslim populations who resided there, traditionally held the view that food was naturally halal, without the need of specific certification procedures. Later on however, the increase of food imports changed this situation, and so Muslim-majority countries also developed their own halal standard [4].
The regulatory frameworks in the halal sector are therefore somewhat complex, as they vary from one geographic area to another. The differences between the Islamic schools originated in the early Islamic era, and are much more complicated nowadays in a wider geographic perspective and in a globalized world. The regulation of the halal market is still evolving. Different halal standards have been established among different countries and, sometimes even within each country, due to the presence of several issuing organizations and authorities.
Consequently, there is currently no consensus on a single halal standard. This generates uncertainty for producers, who may not know exactly which authority to consult in order to get their product certified for the selected market. In addition, another consequence of the multiplicity of halal standards is that producers from either non-Muslim countries, or from Muslim countries where a different standard is recognized, are required to obtain additional halal certifications according to each geographic area where they intend to export. Therefore, a global halal standard would be very much welcomed by the food industry. Last but not least, the multiplicity of standards (and consequently the multiplicity of different halal marks to be included in the food label) causes confusion among consumers too and might decrease their overall trust in certifications.
The LPPOM MUI is an Indonesian institution aimed at carrying out halal certification processes in the sector of foods, drugs, and cosmetics. The LPPOM, whose members are qualified in chemistry, biochemistry, food science and technology, and agro-industry, was established in 1989 to assist MUI as a halal certifying body in Indonesia, the biggest market of halal food products in Asia [33]. To get the halal certificate, a company must implement a halal assurance system that ensures the continuity of halal production processes during the validity period of the certificate [34].
The MS 1500 standard, first issued in 2000, obtained its third revision in 2019. This standard provides practical guidance for the food industry on the preparation and handling of halal food in Malaysia. The halal certification is issued by a federal authority, specifically by a religious department of the government, the JAKIM. The Malaysian standards have been considered as a model for halal certification by the Codex Alimentarius Commission [34] and have been used as the basis of halal standards in many other countries [6].
The GSO, established in 2001 and having operated since 2004, has the national departments for standards and specifications of the Arab Gulf states (Saudi Arabia, Qatar, Kuwait, Oman, Bahrain, United Arab Emirates), among its members. One of GSO's main functions is to issue Gulf Standards/Technical halal regulations through specialized technical committees (TCs) [35].
It has to be considered that each National Standardization Body in GSO member countries is obliged to adopt the GSO standards, eliminating any conflicting national standards. Therefore, GSO Standards become the national standards in all the Arab Gulf countries [35].
In the case of importing meat and meat products (or other food products) in any of the Arab Gulf countries, the halal certificate accompanying these products must be checked by the consulate of the importer country. The check is fundamental to verify that the issuer of the certificate is accredited by the concerned agencies, according to the requirements mentioned in the GSO standard. Such certificate shall reflect that slaughtering and production have been done as prescribed by the GSO standard and in accordance with national laws and regulations. Meat and meat products must have a food grade stamp affixed by the issuer of the certificate or by an Islamic center or institution, so that it cannot be counterfeited [31].
The OIC is an alliance of countries in which Islam plays a significant role, including countries where Islam is the state religion, those in which Muslims represent the majority of the population, and those in which Muslims are only a minority but play a significant role for the country. In the latter category are countries such as Uganda, Benin, Togo, Mozambique, the Ivory Coast, Gabon, Cameroon, Suriname, and Guyana. The OIC has General requirements for halal food currently 56 member countries (Fig. 4), spread over four continents, primarily in North Africa, Middle East, and Central Asia [36]. The 10 biggest food markets in the OIC countries are: Egypt, Saudi Arabia, Iran, Iraq, Turkey, Pakistan, Bangladesh, Nigeria, Algeria, and Indonesia [4]. Under the OIC, the designated organization for the development of standards is the SMIIC, established in 2010. The OIC/SMIIC has the objective of providing a unified framework whereby all the OIC member states use the same standards and methodologies for certification, accreditation, and laboratory services, in order to facilitate commercial exchanges [37]. Various other bodies actively collaborate with SMII C, such as the Emirates Standards and Metrology Authority (ESMA) and the Turkish Accreditation Agency. However, the OIC/SMIIC standards may not be recognized by the member countries that had already issued and adopted their own halal food standard, such as Indonesia and Malaysia.

Attempts to harmonize the halal standards
Several attempts have been made to harmonize the existing halal standards, along with their certification and accreditation procedures. However, although these attempts should be duly credited with conceiving the idea of a transnational cooperative organization, no unification has yet been achieved because of the very reason that several of these organizations (named, depending on each individual case, "council", "forum", or "alliance") have been constituted. There is still a long way to go to achieve a unified halal standard. The idea of establishing a reliable system for the harmonization of standards among Islamic states can be traced back to the 1st Meeting of the Economic and Commercial Cooperation Standing Committee (COM-CEC) of OIC in 1984 [38]. The Standardization Experts Group for Islamic States (SEG) was established in 1985 for this purpose, and its work led to the approval of the SMIIC Statute at the 14th COMCEC Meeting in 1998 [38].
The World Halal Food Council (WHFC), founded in 1999 upon the initiative of the LPPOM MUI, represented another attempt to harmonize the halal market, with the aim of defining a global halal standard [39]. In 2011, around 20 halal certifying bodies around the world had joined the WHFC [39]. The establishment of a Minimum Core Standard including a number of basic issues (such as pork and alcohol prohibition) was suggested, with specific additional requirements applied to each individual country [40]. The WHFC is currently still working on controversial topics pertaining halal dietary laws.
During the 2006 World Halal Forum, a similar attempt was made by establishing the International Halal Integrity (IHI) Alliance, an international association aimed at the development of a global halal standard to uphold the integrity of the halal industry [40].
The harmonization of the accreditation practices in the halal sector worldwide was also considered. A step forward in this direction was the establishment, of the International Halal Accreditation Forum (IHAF) in 2016, a network of halal accreditation bodies (HABs) [41]. Accreditation of halal certification bodies (HCBs) is a fundamental step in ensuring their reliability and objectivity during the certifying process. Acting as both a certifier and an accreditation agency may, in fact, lead to Fig. 4 Map of the 56 countries members of the Organization of Islamic Cooperation (OIC) (from WorldData.info, https://www.worlddata.info/ alliances/oic-organization-of-islamic-cooperation.php). The OIC is a worldwide organization of Islamic countries, with the main objective of promoting socio-cultural and economic cooperation among them. The majority of member countries is located in North Africa, Middle East, and Central Asia, but there are also a few members from South America (Suriname and Guyana) and Europe (Albania) conflicts of interest. However, a number of HCBs have not fully embraced the concept of accreditation and operate as unofficial HABs [4]. The first meeting of IHAF was attended by 10 constituent members including several western countries, such as Australia, New Zealand, the UK, the USA, and Spain [41]. The number of members then increased to 27 HABs, operating both in the OIC member countries and in non-Islamic countries [41].
A case study: comparison of different halal standards applied to slaughterhouses Dhabiḥah are techniques that are acceptable in the halal slaughtering of all permitted animals and birds. The basic requirements related to slaughtering are common to all the major halal standards. For example, the size of the knife used for slaughtering should be proportionate to the neck, and there should be as little back and forth strokes as possible. The slaughterer must be trained to minimize damage to the skin and carcass while cutting the front of the neck, in order to sever the jugular and carotid, esophagus, and trachea, without reaching the nerves and bones [14]. However, some aspects of slaughtering may vary according to the halal standard considered [42]. For example, the requirements related to slaughtering according to the GSO 993:2015 [31], OIC/ SMIIC 1:2019 [32], HAS 23103:2012 [28], and MS 1500: 2019 [30] halal standards, listed in Table 3, show several differences. Even the Codex Alimentarius Commission, when defining the general guidelines for the use of the term halal, recognized that "there may be minor differences in opinion in the interpretation of lawful and unlawful animals and in the slaughter act, according to the different Islamic schools of thought" [13]. Therefore, slaughterhouses looking to obtain a halal certificate for their meat products have to fulfill specific requirements depending on the standard they choose to adhere which, in turn, depends on the specific geographic area where the products are to be marketed.
According to MS 1500:2009 [30] and HAS 23103:2012 [28] standards, the location of the manufacturing site must be separated from pig farms. The HAS 23103:2012 standard specifies that the closest pig farm, if present, must be at least 5 km from the halal premises [28]. Due to the high concentration of pig farms in Europe compared to the countries where these standards were set up, it may be difficult to fulfill these requirements for slaughterhouses in Western countries, not to mention that most of them usually slaughter pigs as well as other animals. On the other hand, the OIC/SMIIC 1:2019 standard states that the slaughtering site must be dedicated exclusively to halal animals and halal slaughter [32], whereas the GSO 993:2015 standard does not mention any specific requirement regarding the location of the manufacturing site [31].
Slaughtering tools must cut by sharpness of their edge, and not by weight or pressure, but this point is considered only by GSO 993:2015 [31] and OIC/SMIIC 1:2019 [32]. All the considered halal standards agree that the halal and non-halal animals shall not be slaughtered on the same production line. Halal food must not come into direct contact with tools or food products that are non-halal, for these are considered a contaminant. Specific procedures (i.e., "ritual cleaning", described in the next paragraph) are required by the OIC/SMIIC 1:2019 [32], MS 1500:2009 [30], and HAS 23103:2012 [28] standards to convert all production lines or tools that have come into contact with contaminants (najis) to halal status. The GSO 993:2015 standard, meanwhile, considers the general (not ritual) cleaning rules as sufficient and does not require the conversion process to be repeated on a continual basis [31].
There are three categories of najis, which vary in severity, with the more extreme najis being considered particularly serious by Islamic law (Table 4). In case of severe najis, appropriate cleansing (called samak or dibagh) must be done, which involves 7 steps of washing including one with water mixed with soil/clay [30]. These requirements are somewhat difficult to apply in European slaughterhouses, where personnel are not familiar with the halal precepts. Furthermore, the use of clay or soil may well be rejected by the HACCP internal quality control. With the purpose of facilitating halal cleansing, the use of a cleaning product containing soil is permitted [28,30,32], and liquid clay-based products which can be used as ritual detergents are widely sold and marketed in Indonesia [43]. The particle size of clay must be small in order to avoid damaging equipment surfaces [44]. The ritual cleansing by using clay is an example of qiyās (analogical reasoning) based on the following procedure mentioned in Sunnah: "The purification of the utensil belonging to any one of you, after it is licked by a dog, lies in washing it seven times, using sand for the first time" (Sahih Muslim, 821-875 AD).
It should be noted that the ritual cleansing procedure imposed by three of the four standards examined, namely OIC/SMIIC 1:2019, HAS 23103:2012, and MS 1500:2009, is the procedure defined by the Shafi'i school, without taking into account other fiqh schools, such as the Hanafi and the Maliki, who consider washing it seven times with running water without clay or soil [17] sufficient, or the Hanbali school, which recognizes a detergent, namely "soap", as an equivalent substitute to clay/soil [17], this being an approach that is more practically applicable to today's modern lifestyle. Slaughtering site, tools, utensils, devices, machinery The slaughterhouse productive site shall be effectively segregated and well insulated from pig farms or their processing activities to prevent contamination through personnel and equipment × × The closest pig farm, if present, has to be distant at least 5 km from the halal premises × The slaughtering site shall be dedicated only to halal animals and halal slaughter ×

Permitted animals
Halal animals × × × × The animal must be alive or deemed to be alive before slaughtered × × × × The animal must be healthy (approved by a veterinary authority) and the principles of animal welfare must be respected × × × ×

Stunning
Stunning must not kill or cause a permanent physical injury to the animal × × × × Stunning should be made only to reduce animal pain and make slaughtering easier × × × × The stunned animal should be alive or deemed to be alive before slaughtering starts × × × × The veterinary authority must supervise the stunning process × × Stunning tools must be free from any non-halal material × × × × Stunning should follow specific instructions in terms of intensity (stunning type, duration, voltage, and position of stunner) Stunning tools must be calibrated and validated periodically by the competent authority × × × The only permitted stunning methods for bovines are electrical or pneumatic percussive stunning (non-penetrative captive bolt stunning, ax/hammer, or air blowing) The only permitted stunning method for poultry is electrical stunning (water-bath stunning) × × Stunning should be avoided except for violently resisting animals ×

Stunning operator
The stunning operator must be skilled and pass the training conducted by halal certification bodies or other competent authorities ×

Slaughtering
Right before slaughtering the animals, the slaughterer shall utter "In the name of Allah" (tasmiyah "Bismillah") and he shall not mention any name other than Allah, otherwise this will make meat non-halal The slaughter act shall be done intentionally and in the name of Allah × × The slaughter act shall sever the trachea (halqum), esophagus (mari) and both the carotid arteries and two jugular veins (wadajain) to enhance the bleeding and death of the animals. The bleeding shall be spontaneous and complete Regarding the permitted animals, there are no differences among the standards considered: animals must be healthy, alive (or deemed to be alive) prior to the slaughtering act, and from permitted species.
Regarding pre-slaughter stunning, aimed at inducing unconsciousness in order to minimize the pain associated with slaughter [45], the major halal standards permit stunning but do not encourage it. Stunning is permissible as long as the animals and poultry do not

Halal supervisor
The supervisor shall be minimum 18 years old × × The supervisor shall practice Islam as a good Muslim × × The supervisor shall pass a training by halal certification body or competent authority × × The supervisor shall ensure that the stunning process (if any) does not cause permanent physical injury or death; that the slaughtering process meets the halal requirements; that the animals are dead before further handling; that non-halal products are not mixed with halal products, either in chiller, deboning room, cold storage, and transportation; that appropriate records of all the activities are kept × × There must be an adequate number of supervisors per day, adjusted with the number of animals being slaughtered × × The supervisor is responsible for the effectiveness of the halal internal control system ×

Halal head checker
The halal head checker must be a practicing Muslim and technically competent × The halal head checker must be trained and supervised by a halal certification body × The halal head checker must verify the halal carcass status by examining the level of damage × × The halal head checker must assess the skull damage after stunning and record for any noncompliance carcass × ×

Halal checker
The halal checker shall be minimum 18 years old × The halal checker shall be healthy and mentally sound, as proven by medical record × The halal checker shall practice Islam as a good Muslim × The halal checker must be trained and supervised by a halal certification body × The halal checker must check all the activities related with stunning and/or slaughtering × die instantly as a result of stunning itself. Stunning should therefore be "reversible", i.e., non-lethal [46]. Stunning should be performed at a certain degree of intensity approved by health and Islamic authorities. There are several means and methods of stunning used for different animals and poultry species. In particular, two of the examined halal standards accept electrical stunning (water-bath stunning) for poultry and mechanical stunning (pneumatic percussive stunning and non-penetrative captive bolt stunning) for other animals [28,30,32]. Stunning is an effective method to ensure the animal avoids feeling pain, but some studies claim that it has adverse effects on carcass, meat quality, and public health [47,48]. In contrast, other studies [49,50] found that the physicochemical and quality properties of goat meat from electrically stunned animals were comparable to those of animals slaughtered without stunning. Moreover, no differences in bleeding were observed comparing stunned sheeps with non-stunned ones [51].
At a European level, a number of regulations have been implemented over the years to protect the welfare of animals during slaughter. This issue was given importance for the first time in 1974 with the 74/577/EEC Directive [52], setting out measures for animal protection at the time of slaughtering or killing. This framework was further developed by the 88/306/EEC Directive [53], and the 93/119/EC Directive [54], the latter repealed by the Council Regulation (EC) 1099/2009 [55].
The first measure introduced was aimed at ensuring that animal death was as rapid as possible after stunning, in order to avoid any cruelty to animals [52]. Art. 3 of EC Reg. 1099/2009 [55] reiterates that animals shall be spared any avoidable pain, distress, or suffering during their killing and related operations. Stunning, which causes animals to be unconscious, should last until they are slaughtered, thus avoiding any unnecessary suffering.
Pre-slaughter stunning, however, has divided the opinion of scholars within the Muslim community [56,57]. Many scholars in the UK, for example, consider reversible electrical stunning to be compatible with halal slaughter [56], but many people will not accept meat from stunned animals [57]. In general, all forms of stunning and unconsciousness of animals are disliked because the severity of stunning might kill the animals before bleeding, which is unacceptable for halal. The issue of stunning for religious slaughtering is well known and even EU rules are on board with this. According to the Council Regulation (EC) 1099/2009 (art. 4.4) [55], in the case of animals subjected to particular slaughtering methods prescribed by religious rites, stunning is not obligatory, provided that the slaughter takes place in a slaughterhouse. Some countries, however, such as Sweden, Norway, Iceland, Denmark, and Slovenia prohibit any ritual slaughtering without stunning [58].
According to OIC/SMIIC 1:2019 [32] stunning and concussion (loss of consciousness) should be avoided except for animals who are violently resistant. MS 1500: 2009 [30] does not recommend stunning but, if it has to be carried out, specific conditions are set by this standard. HAS 23103:2012 [28] allows for stunning, specifying that its sole objective is to ease the slaughter process and minimize animal pain.
The four halal standards set out guidelines on the intensity and duration of stunning to ensure that animals remain alive during and after stunning. If animals die before slaughtering, they shall be deemed as fatally beaten (mawqouza) and, therefore, considered haram. With regards to this, however, it should be considered that the verse 05.03 of Surat Al-Maeda (the table) states that "Forbidden to you (for food) are: Al-Maitah (the dead animals), blood, the flesh of swine, that on which Allâh's Name has not been mentioned while slaughtering, the strangled, the (Mawqouza) dead through beating, the Remove the contaminant and wash seven times with running water, one of which shall be with water mixed with soil. The first wash shall clear the najs. The water from first cleaning shall not remain behind and the successive wash shall be counted as the second wash. The amount of soil used is just enough to make a suspension.
dead through falling from a height, that which had been killed by (the goring of) horns, and the devoured of wild beasts, unless you are able to slaughter it". According to this verse, the specification "unless you are able to slaughter it" poses an exception, i.e., the case of a freshly dead animal (who has died in front of the person). This point should therefore encourage revision of the current opinion about stunning, i.e., even in cases that make the animal die, provided that the slaughtering process is completed within few minutes from stunning and complies with the requirements on bleeding, the animal can still be consumed. EU legal framework, specifically 64/ 433/EEC Directive [59], 93/119/EC Directive [54], and EC Reg. 1099/2009 [55] also states how bleeding must be complete and operations of stunning, shakling, hoisting, and bleeding must be carried out consecutively on one animal before carrying out any of them on another animal. This situation is similar to that of animals hunted by means of trained animals: in verse 05.04 of Surat Al-Maeda; it is stated that you must still pronounce the name of Allah over these hunted animals, even though, in many cases, the prey is already dead. The most important issue is that the animal is healthy, not rotten or diseased, and immediately slaughtered, as mentioned in the hadith "If you shoot with your arrow and (the Prey) goes out of your sight and you find it (later on), then eat if it has not gone rotten" (Sahih Muslim, 821-875 AD). Slaughter is designed to remove all blood from the carcass by a complete bleeding process. There are several factors which are responsible for bleeding efficiency after slaughtering, such as the physical state of the animal before slaughter, the stunning method, and the interval between stunning and bleeding. During Islamic slaughter, it is very important to maintain the connection between the brain and the rest of the body via the spinal cord, by ensuring the prevention of neck separation, in order to send the nerve signals and hormonal alerts needed to complete the bleeding process [14].
Regarding the slaughterman, all the considered standards require this person to be Muslim, with the exception of GSO 993:2015 [31], which also allows Jews and Christians to fill this role. In the past, Muslims living in Europe did not question the halal status of meat, even slaughtered after stunning, because they regarded meat slaughtered by Christians and Jews, i.e., "People of the Book", as halal [60]. The HCBs should keep a record of the names of the halal slaughterers (muthakeen) and supervisors, and a record of the supervision procedures [6]. The roles of the halal supervisor and head checker are only specified in the HAS 23103:2012 [28] and MS 1500:2019 [30] standards. The role of the halal checker is only stated in the MS 1500:2019 standard [30].

Conclusion
The growing demand for halal products motivates manufacturers to comply with halal standards, in view of potential commercial benefits. Halal certifications, however, are released by a number of bodies which may differ in the requirements imposed, as shown in the case study of slaughterhouses. Therefore, a specific halal certification is not recognized worldwide. The implementation of a harmonized monitoring system and establishment of a unified global halal standard would facilitate trade and increase the confidence of both producers and consumers. This study evidences that several attempts have been made to harmonize the existing halal standards. However, no unification has been achieved so far, and further efforts by standardization organizations are still needed to overcome this challenge. Only close collaboration between authorities from all the different countries involved in issuing halal certifications can lead to a homogeneous regulatory framework with unified certification and accreditation procedures, increasingly required in a globalized market.