What Is Sashimi or Sushi Grade Fish? The Detailed Guide.

The terms sushi or sashimi grade describe fish or seafood suitable for raw consumption. While the term may seem quite authoritative, as it stands today it is neither defined nor standardized. It is more of a generally accepted marketing term used to help customers select certain ingredients or to promote the sale of certain fishery products.

"There is no standard legal definition of sashimi grade. When you see marine fish labeled as such, it simply means the seller has determined that the fish is probably good for sushi, based on an assessment of bacteria levels, temperature, parasites, appearance, smell, taste, how it’s displayed, and time after being caught. For the consumer, it is a question of whether you can trust the seller." [Sakagami, 2019]

Nick Sakagami

Osakana-Master

Consequently, many commercially available fish or seafood are suitable for the preparation of sushi or sashimi, provided they meet certain quality and safety criteria. With regard to these requirements, exact guidelines and standards exist in many countries. They regulate how fish or seafood must be handled if they are to be consumed raw. In particular, these regulations usually deal with the specifications for maintaining the necessary cold chain, hygiene and the killing of potential parasites that are potentially harmful to humans. Because the preparation of sushi or sashimi is only one of many possible raw dishes, the relevant regulations are therefore less concerned with qualitative (organoleptic) characteristics such as taste, appearance, odor and color than with food safety. Nevertheless, these very characteristics, along with freshness and safety, play a central role in the selection of ingredients for the preparation of sushi and sashimi.

The following paragraphs explain the basic requirements for the general definition of sushi or sashimi grade. Since sushi has long since become a global culinary phenomenon, consumers today usually encounter this term at fishmongers, supermarkets or various online stores. It should be mentioned that the term sushi or sashimi quality generally describes suitability in terms of food regulations and not "quality" in particular. The quality spectrum of suitable and "safe" ingredients therefore ranges from inexpensive mass-produced goods to high-priced top-quality products.

Fish or seafood should be as fresh as possible for the preparation of sushi or sashimi. Ingredients that need to aged for a certain time before they develop their best flavor should also have a high degree of freshness at the beginning of the aging process. In the context of food, the term "freshness" is used as a definition for the condition of an ingredient whose original characteristics are preserved as much as possible. Spoilage is thus an indicator of changes after catch or slaughter. Compared to other food, fish and seafood are highly perishable and therefore require special requirements in their handling and processing.

Raw fish and seafood are among the most sensitive foods from a microbiological and hygienic point of view. The spoilage process is triggered by the action of enzymes, bacteria and chemical reactions. Therefore, the longer the time of death, the more advanced the growth of potential pathogens. Therefore, when using raw ingredients, a certain basic level of germ contamination should always be assumed. As expected, processing and preparation further increases this germ content. This underlines the importance of freshness and the quality of the initial product, because sushi or sashimi is usually consumed raw, without prior (germicidal/bactericidal) heating.

The spoilage process is usually accompanied by a change in the physical characteristics of the raw material. These changes result in deterioration of food quality such as color, texture and taste. While both freezing and refrigeration extend the shelf life of food, objective food quality continues to deteriorate regardless of the preservation method [Dawson et al., 2018]. Therefore, fish and seafood, whether processed into sushi or sashimi or stored, should be as fresh as possible.

The definition of "fresh" or is often colloquially equated with the absence of a freezing treatment. However, freezing fish or seafood does not reduce its freshness, but rather serves to preserve it. However, it remains to be considered that while freezing does extend the shelf life of food, it equally inevitably leads to a degradation of food quality [Dawson et al., 2018]. The physicochemical and biochemical reactions that regulate food deterioration are slowed but not stopped when foods are frozen. During storage, the organoleptic quality gradually deteriorates but does not become objectionable for a long time [Sebranek, 1996]. The temperature at which frozen foods are stored, the length of time they are stored, and the thawing process all play a role in quality loss. Careful management of these processes, including preparation before freezing and thawing, it is possible to provide frozen fish or seafood with a high level of quality [Rahman & Velez-Ruiz, 2007].

Raw consumption of fresh, previously unfrozen fish or seafood carries a risk of being contaminated with viable parasites that may be harmful to humans [Nawa et al., 2005]. Fish or seafood caught in the wild are particularly problematic in their evaluation for potential parasite infection.

Candling or rapid visual inspection on a light table is a common practice in the fish processing industry to detect nematodes. The success rate depends on fillet thickness, size, texture, color, and fish species, and is largely dependent on the training and skills of the inspector. As a result, candling is insufficient to detect the majority of nematodes present in the meat [Llarena-Reino et al., 2012]. Epidemiological data from fishing areas can provide information on the risk of possible parasite infestation [Cipriani, 2018], but are not an absolute guarantee of the absence of parasites in wild fish [EFSA, 2010]. Particularly with regard to raw consumption, it is necessary to ensure that there are no viable parasites in the meat. According to U.S. Food and Drug Administration (FDA) regulations, to kill parasites, the following core temperatures and storage conditions must be met; otherwise, fish or seafood is not safe for raw consumption unless exempt conditions exist [FDA, 2020].

• Freezing at an ambient temperature of -4°F (-20°C) or below until solid. Storing at an ambient temperature of -4°F (-20°C) or below for 7 days; or
• Freezing at an ambient temperature of -31°F (-35°C) or below until solid. Storing at an ambient temperature of -31°F (-35°C) or below for 15 hours; or
• Freezing at an ambient temperature of -31°F (-35°C) or below until solid. Storing at an ambient temperature of -4°F (-20°C) or below for 24 hours.

Most household or domestic freezers are not capable of ensuring a continuous temperature of at least -4°F (-20°C) or below. In addition, the study by [Podolska et al., 2019] shows the importance of the speed of the freezing process and that longer storage times must be considered accordingly. Freezing in household or domestic freezers for the sole purpose of killing parasites should therefore be discouraged [Sanchez-Alonso et al., 2018].

Professionally and industrially frozen fish or seafood, in contrast to freshly caught seafood, have the advantage that they can be stored considerably longer without significant loss of quality. Freezing is one of the most effective forms of food preservation. Microbial growth that cause food spoilage and pathogens are deactivated below of -0.4°F (-18°C). By using industrial flash freezing, food quality degradation is minimized [Iwata et al., 2015]. Fish or seafood that have been preserved by flash freezing immediately after being caught are thus adequate and satisfactory ingredients for the preparation of sushi or sashimi.

All frozen foods are suitable for consumption, as long as they were edible at the time of freezing. Frozen foods have an almost indefinite shelf life in terms of food safety; any expiration date claims generally refer to organoleptic food quality ([FoodFacts, 2020], [Schafer & Driessen, 2018]). Because food quality plays a central role in the preparation of sushi and sashimi, ingredients should not be stored in domestic freezers for an extended period of time. Although the ingredients are still edible, the quality continuously deteriorates as enzymatic and non-enzymatic changes also occur during frozen storage, albeit at a much slower rate [Moharram & Rofael, 1993]. Sushi ingredients that have been previously been frozen should not be frozen again after thawing because pathogens reactivate and begin to grow throughout the thawing process. In terms of food safety, as well as aesthetics and taste, fish or seafood that has been thawed under refrigeration should be prepared and consumed in a timely manner.

Frozen food often has the reputation of being inferior to fresh. From an organoleptic point of view, fresh products that are adequately cooled and consumed in a timely manner have the advantage. Freezing, especially slow freezing, can negatively change the textural qualities of products. However, with flash freezing, these qualities are better preserved, and the differences from a fresh product are very slight to partially imperceptible. The extremely short freezing process during flash freezing ensures that the cell liquid forms only very small ice crystals, so that the cell structures remain intact. The degree of cellular damage is directly related to food quality in terms of taste, texture, nutritional value, and appearance [Goswami, 2001]. Modern processes allow fish and seafood to be preserved without significantly deteriorating their quality or nutritional value.

If fish or seafood has been farmed (aquaculture), the freezing treatment required for raw consumption may be waived under certain conditions. In the case of the requirements for safe raw consumption, for example, the regulations of the European Commission go further than those of the U.S. Food and Drug Administration, which state that [EC 1276/2011]:

1. Use of animals cultured exclusively from embryos.
2. Those animals have been fed exclusively on a diet that cannot contain viable parasites that present a health hazard
3. The rearing of the animals must take place in an environment that is epidemiologically proven to be free of parasites or the farm operator uses officially approved procedures to ensure that no viable parasites are present in the products and therefore do not pose a health hazard, this requirement may be waived.

Farmed fish and seafood raised in land-based tanks or closed recirculating systems are considered safe with respect to the presence of parasites that pose a health risk, provided the above conditions are met [EC 1276/2011].

The U.S. Food and Drug Administration maintains a list of species whose risk of infestation with parasites harmful to humans is considered high, but further recommends an individual assessment of the situation with regard to raw consumption even for low-risk species [FDA, 2020].

"Species of fish not listed with a parasite hazard [...] may have a parasite hazard that has not been identified if these fish are not customarily consumed raw [...], or if the hazard occurs in certain localized harvest areas that are not known commercial sources of fresh fish for the U.S." [FDA, 2020]

U.S. Food and Drug Administration

Fish and Fishery Products Hazards and Controls Guidance, Chapter 5

According to the European Commission, parasite-killing freezing treatment of wild-caught fish or seafood may be not required if epidemiological data indicate that the fishing grounds of origin do not pose a health risk in terms of parasite occurrence, and the competent authority authorises [EC 1276/2011].

Farmed Atlantic salmon (lat. Salmo salar) raised in floating cages (marine aquaculture) has a low probability of parasite infection, according to the European Food Safety Authority (EFSA). Apart from Atlantic salmon, there are insufficient surveillance data for other farmed species. It is therefore not possible for EFSA to currently identify other fish species or seafood from marine aquaculture that do not pose a health risk in terms of the presence of parasites [EFSA, 2010].

Not all fish species are used untreated for the preparation of sushi or sashimi. For example, mackerel, Pacific herring or young sea bream are regularly pickled in an acidic solution of salt, vinegar, soy sauce or other ingredients. A popular Japanese method includes pickling or marinating in a vinegar solution (sujime). Sujime is commonly used to soften bones, enhance flavor and preserve meat. A popular sushi or sashimi ingredient made using this method is shime saba. Marinating may cause an antibacterial effect, but has little effect on potentially present parasites. Although some cooking- or sushi- literature may encourage killing parasites by pickling or marinating [Mouritsen, 2009], studies show that traditional marinades are ineffective and thus are not an adequate alternative to freezing treatment [Sánchez-Monsalvez et al, 2005]. An exception is the traditional German or Danish method of marinating herring fillets. However, this method requires a storage period of at least 5 to 6 weeks in an 8-9% saline solution to ensure that all parasites are killed [Karl et al., 1994]. To reliably kill parasites with a salt and vinegar solution within a short time, the pH would have to be so low that the meat would be almost unpalatable.

As we all know, taste is debatable, but quality is not. For an optimal taste experience when eating sushi or sashimi, the raw ingredients should therefore be of very high quality. Exceptions are fish that have already been dry aged for flavor enhancement. During this controlled aging process, their objective quality characteristics deteriorate, while the taste intensifies.

Whether you prefer fatty fish like salmon or lean fish like sea bass, the better the quality, the tastier the final dish. Therefore, from the consumer's point of view, it is important to be able to distinguish between high quality and lower quality raw ingredients. Likewise, origin and seasonality are important, especially for wild-caught species. Climatic influences and timing of spawning have significant effects on overall physiology, fat content, and thus have a direct impact on taste [Sarower et al., 2012], [Hwang et al., 2000]. Purchase price is not necessarily an indicator of quality or taste. Nevertheless, it is regularly shown that quality and taste are often associated with a higher price. Especially in the case of farmed fish, experience shows that fish from high quality farms, are superior to those from ordinary aquaculture. Especially when the fish are to be processed into sushi or sashimi, those products have the advantage whose breeders rely on low stocking density, careful handling and special slaughtering methods (e.g. ikejime).

Most of the wild fish available in the trade come predominantly from commercial or industrial fisheries. Possible fishing methods range from pole and line to kilometer-long trawls. Basically, any fishing method can be used to provide "sushi" or "sashimi-quality" fish. On the other hand, the fishing method may well be responsible for the difference between top and normal quality [Satomi, 2016]. The more sought-after a species is, the more likely it is that fishing methods will be differentiated in terms of quality, as in the case of tuna.

After you have decided what kind of fish you would like to buy, you need to evaluate the quality of the fresh seafood you have chosen. Whole fish, regardless of the variety, have certain characteristics that indicate freshness.

Unlike whole fish, it is much more difficult to tell how "fresh" fillets are because the number of indicators is significantly reduced. Fillets that have been filleted by hand, if processed properly, are preferable to those from automated and industrial processing. When removing the fish bones by machine, cracks or indentation may be added to the meat. The damage is not only unsightly, but also provides a potential breeding ground for bacteria. Condensation can collect in the cracks, which can promote the growth of bacteria. If filleted pieces are pale and dry or covered with some sort of slimy layer, refrain from using them. Pre-packaged fillets should not contain excessive liquid, which can be an indication of temperature abuse or excessive storage. In addition, the liquid promotes faster spoilage of the fillets.

Fish or seafood used for the preparation of sushi or sashimi must be fresh and should comply with the aforementioned specifications. Both wild-caught marine and freshwater fish must be assumed to be infested with viable parasites that may be of concern to human health. Common methods of detecting possible infestation by parasites, in addition to purely diagnostic laboratory methods, include candeling and visual inspection during filleting. However, these conventional or visual inspection-based methods are error prone and cannot be applied to large species or unprocessed fish or seafood. It is therefore considered unlikely that wild-caught fish without proper anti-parasitic freeze treatment are fundamentally a safe raw ingredient for the preparation of sushi or sashimi. Although traditionalists prefer animals without prior freezing treatment, it is advisable in terms of food safety to subject all wild-caught fish and seafood to industrial flash freezing. High quality processed fish or seafood that has been flash frozen in a timely manner after being caught and properly thawed is comparable to those that have not been frozen. This method should only be dispensed with if it is undoubtedly ensured that the respective ingredient is free from viable humanpatogenic parasites. For those who value fish or seafood that is as fresh as possible and without freezing treatment, fish or seafood from approved aquaculture facilities may be an adequate and safe alternative.