Losses of actually edible food occur wherever food is produced or processed, mainly at the beginning of the value- adding chains. Typical examples of this are slaughterhouse waste, and poor raw materials that lack quality or food safety. Food waste, on the other hand, tends to occur at the end of the supply chain, for example because the best-before date has passed, too much has been bought, the food was not prepared properly in the kitchen, the fish dish did not turn out as expected, or was simply forgotten in the refrigerator. There are many different reasons why a food product finishes up in the bin but each individual case represents a waste of valuable resources. Reducing food losses and waste improves food security for many people, reduces the ecological footprint of food production and, in the overall balance, also lowers production costs. Although much of the data available on this problem is based only on estimates, the extent of global food waste is alarming. An FAO study has calculated that an inconceivable 1.3 billion tons of food are lost every year, which corresponds to nearly 2,500 tons per minute (!). This quantity would probably be enough to completely eradicate world hunger. And not only that: more complete use of resources would also slow down the permanent growth spiral in production, remove the basis for land speculation, and probably lower food prices. The World Bank has calculated that reducing losses is ultimately “more cost-effective and environmentally sustainable” than increasing production by the same amount. Given this significance, it is not surprising that Goal 12 of the UN Sustainable Development Goals (SDG) aims to halve global food waste at retail and consumer level by 2030. In order to quantify more accurately the progress achieved in this area, the FAO and the UN Environment Programme (UN Environment) have developed a new evaluation method. The Food Loss Index (FLI) shows how much food is lost in production or in the supply chain before it reaches the retail trade. The Food Waste Index (FWI), on the other hand, reflects the amount that is wasted by retailers and consumers. In the past, losses and waste were calculated only by quantity, not by economic value. Since this can lead to misinterpretations the FAO now also includes in its calculations the products’ economic value. Based on the new calculation method it is now assumed that nearly 14% of all food worldwide is lost after harvest or catch before it reaches the trade sector. However, losses vary considerably not only within the different commodity groups and at the individual stages of the supply chain but also by region, and this makes any generalisations difficult. But one thing is clear: we consumers have a central role to play in reducing food waste. At least in Western countries, where the rampant “throw-away mentality” of some consumers is responsible for almost two thirds of food waste.
Some fishes offer much more than just fillets
In globalised markets many products travel long distances before they are consumed. A large number of players are involved in ensuring that our fish is caught or produced, processed and refined, cooled, packed and transported in an appropriate manner before it finally arrives on the supermarket shelf. Although the fish industry already makes good use of many fish by-products the FAO’s SOFIA Report 2020 states that an estimated 35% of global fish supply is still lost annually during fishing and aquaculture. This includes, above all, heads, intestines, skin, bones and scales that occur when fish is processed for human consumption. Much of this quantity is used to produce fishmeal but many by-products actually have greater potential and could be used for higher quality products. A first step towards more complete utilisation of fish would be for processors, cooks and consumers to realise that fish does not only consist of fillets or loins. It would ease the pressure on high-demand fish species if all parts of the fish were actually used and new creative ideas for exploitation were developed. There are various reasons why a relatively large share of fish is lost. In recent times, for example, more fish has been processed via gutting and filleting to convenience products, which inevitably results in more waste. Gastronomy and catering require carefully calibrated products where exact weights can only be achieved from a natural product like fish through additional trimming. In some tropical countries, infrastructures are not sufficiently developed, the network of roads and tracks is in poor condition, and the electricity supply is unstable. This makes it more difficult to cool the fish and lengthens transport times, which in turn leads to quality losses and high after-harvest losses. Admittedly, it will never be possible to completely avoid waste in the fish industry, especially since slaughter yields vary depending on the species, age and body shape. The average edible fillet content of demersal species is estimated at 43% (fluctuating between 30% for redfish and 50% for hake) and of pelagic species such as herring not much higher at around 53%. Body part Share in % Head 25 Backbone 17 Fins and ribs 12 Skin 4 Fillet (skinned) 42 Total 100 Share by weight of cod body parts (relative to the gutted fish) It is therefore in the interest of every fish processor to use slaughterhouse waste as wisely and profitably as possible, bearing in mind that waste disposal often involves additional costs. One way to make more complete use of the raw fish is to remove the residual muscle meat from the bone. This can be done by chemical or mechanical means. The result is a type of minced fish meat that can be used for various products, for example fish fingers, fishcakes and burgers, fish balls, fish sausages and other restructured products. In Scandinavia, fish cakes and fish puddings are popular, while in Japan and other Asian countries the fish mince is more commonly used for surimi, kamaboko or fermented sauce products. Decisive for the intended use is the fish mince quality, and this depends on various factors. Chemical extraction methods allow higher yields, but the resulting minced fish is of inferior quality. Mechanical methods using separators, in which a circulating belt presses the fish slaughter waste against a rotating perforated drum, are therefore usually preferred.
The search for alternative uses has long since begun
An important step towards better utilisation of raw materials is to achieve high slaughter yields, i.e. by minimising waste and making the best possible use of the available material. Currently, the waste is mainly processed into fish meal which is then used in animal feed for aquaculture and agriculture. According to the FAO’s SOFIA Report 2020 the share of byproducts such as offal, carcasses and trimmings in global fishmeal production was between 25 and 35%, depending on the region. In Southeast Asia and other areas of the world fish of inferior quality, so called “trash fish”, is often fed directly to crustaceans and fish in aquaculture or to livestock, mainly pigs and chickens. Other uses include fish silage and fish protein hydrolysates, which can be used as animal feed or as fertiliser on arable crops. Considerable quantities of fish waste are also needed as bait in fishing, for example in lobster and crawfish fishing and pole-and-line fishing for skipjack. Mink farms are also among the traditional purchasers of slaughterhouse waste, but due to increasing bans on fur farming these have little future. On the other hand, demand is rising from specialized maggot farms that use proteincontaining waste as a substrate for insects, especially the black soldier fly. Whereas fly maggots used to be sold to anglers primarily as bait, a lucrative new market is now developing in the aquaculture sector. Fish waste has a very high value potential because it contains valuable minerals, enzymes, flavourings and pigments that can be used in food production and are also needed in agriculture, aquaculture and the pharmaceutical industry. In the laboratories of the pharmaceutical industry, for example, some bioactive molecules that have been isolated from marine sponges, bryozoans and cnidarians are believed to cure cancer. After their discovery, however, these molecules are usually chemically synthesized to preserve the natural stocks of marine organisms. It is possible that individual species such as sponges could soon be produced in aquaculture, however. The list of marine by-products that can be extracted from what we still often call seafood waste is growing constantly. It ranges from fish leather and glue, pharmaceuticals, cosmetics and fine chemicals to pigments, collagen, gelatine and pearl essence. The demand for gelatine made from fish skins increased worldwide following the outbreak of bovine spongiform encephalopathy (BSE), especially as it is more likely to meet some religious requirements (halal, kosher). Shells of shrimps and many other crustaceans are increasingly used to produce chitin and chitosan, which are used for water treatment and in cosmetics, food and beverages, agrochemicals, pharmaceuticals and toiletries. Pigments such as carotenoids and astaxanthin can also be extracted from such crustacean waste. Apart from the fat and vitamin-rich liver of cod (cod liver, cod liver oil), these internal organs are unfortunately hardly used today. The nutrient-rich liver spoils quickly and has to be processed under strict hygiene conditions as soon as possible after the catch which is not easy on long fishing trips. In addition, the liver is often infested with parasites or contaminated with harmful substances that accumulate in the stored fat. In many western countries the tongues and cheeks of some fish species remain largely unused despite the fact that their removal could well be worthwhile: tongues and cheeks are regionally traded at similar prices as the fillets. The main reason for doing without this „extra business“ is often the high price that has to be paid for this work which requires a certain amount of experience. In Norway, the removal of cod tongues is a traditional holiday job for school children, who use it to supplement their pocket money. The most important market for salted and fermented cod heads is Nigeria, where these products are considered delicacies. In Iceland dried fish heads are often preserved in milk or whey before preparation and then eaten as a delicacy. Shark-finning, the removal of the fins of sharks has been rightly banned in many countries. Following this cruel step the sharks are then thrown back into the sea, alive but unable to swim and so helpless. Not everywhere, however, is the ban adhered to. Especially in Asia it is sometimes violated because shark fins are said to have a medicinal healing effect and are in great demand.
Unusual niche products can be worthwhile
Among the classic uses for fish waste and less sought-after fish species are fish soups, fish stocks, bouillons and fish sauces. Fermented fish sauces, which are an indispensable part of the food culture in many Asian countries, have been part of the culinary landscape since ancient times. Garum, also called liquamen, was practically the standard spice in Roman cuisine and was used for both savoury and sweet dishes. French chefs use about a dozen Mediterranean species as a basis for Provençal bouillabaisse, in addition to crustaceans and shellfish, especially small and therefore less sought-after fish such as scorpionfish and John Dory, gurnards, monkfish, conger eel, red mullet, whiting and various perch species. If they are too small to be cut into attractive fillets including them in the famous soup is an extremely worthwhile alternative. Mussel shells, which are obtained during extraction of pure mussel flesh, are often ground and used as an aggregate in road construction. Some producers even provide the material free of charge to avoid paying waste disposal fees. In some parts of the world the shells are burned at temperatures above 800°C to produce high-quality shell limestone, which is used as mortar and is very hard. This practice was also common in Europe until about 1900, but was then increasingly replaced by cement. Shell limestone is also used as a feed additive for chickens which need a lot of calcium to form egg shells, and as a fertilizer. mk