Some of the most flavourful and highly appreciated foodstuffs in many cultures around the world owe their deliciousness to taste compounds developed during fermentation and ageing processes, either by use of yeast, bacteria, moulds, and enzymes or combinations hereof (Mouritsen and Styrbæk, 2014). Fermented products are often considered an integral part of a food culture (Katz, 2012). Well-known examples include fermented milk (cheeses, sour-milk products), fermented beans (soy sauce, miso, nattō, douchi, furu), fermented grapes, fruit, berries, and grains (wine, beer, cider, brandy, bread), fermented vegetables (sauerkraut, kimchi, tsukemono), fermented leaves (tea), fermented fish (katsuobushi, fish- and shellfish sauces, Swedish surströmming), and fermented meats (sausages, hams). In most cases, the liking of fermented foodstuff requires adaptation and in some cases it is an acquired taste.

In the classical culinary triangle proposed by Lévy-Strauss (1983), the raw foodstuff can be changed either by cooking (temperature) into edible foodstuff or by microbiological degradation into rotten and inedible stuff. ‘The ‘cooked’ and ‘the rotten’ then represent culture and nature, respectively. However, the borderline between ‘the cooked’ (prepared) and ‘the rotten’ is not sharp, and different cultures as well as cultures at different times have varying perceptions regarding what is considered edible and what is not. Moreover this ‘culinary borderland’ is a flexibly boundary that is constantly subject to negotiation and reinterpretation (Højlund et al., 2014). Manipulating and mastering fermentation processes is a way to navigate this borderland. As pointed out by Vilgis (2013), by considering fermentation and long-time cooking as a desirably way to degrade proteins and carbohydrates in prepared food, in much the same way as spontaneous degradation in undesirable putrefaction, the borderland between ‘the cooked’ and ‘the rotten’ tends to vanish.

Fermentation releases a range of flavourful taste compounds and aroma substances. Often a repulsive smell can overpower the desire to taste the fermented foodstuff. In many cases the fermentation processes produce a bounty of nutritional elements that are more easily digestible and provide for enhanced bioavailability in the gastrointestinal system. At the same time, properly conducted fermentation leads to preservation and prolonged lifetime of the prepared foodstuff, e.g., via dehydration or production of alcohol and lactic acid that suppress undesired fungal and bacterial growth as well as putrefaction.

In some cases, enzymatically facilitated low-temperature Maillard reactions during the fermentation may release additional flavourful browning products (Nursten, 2005), as is well known, e.g., from soy sauce and black garlic, although the process at low temperatures takes very long time.

The success of a fermentation process applied to foodstuffs is from the point of view of microbiology a delicate balance involving the risks of cross-contamination, wild fermentation outcompeting culturing, and growth of unwanted and potentially hazardous, poisonous fungal and bacterial cultures (Katz, 2012). Cultured fermentation typically requires good measures of cleanliness, temperature control, possible sterilization, and the use of starter cultures. High levels of salt (sodium chloride) and low pH are the most important parameters suppressing the growth of undesired microorganisms and leading way to the degradation of proteins, carbohydrates and nucleic acids.

There is a significant difference in the approaches used to ferment plant matter and meat from animals (Katz, 2012). Plants and foodstuff derived from plants contain large amounts of carbohydrates and sugars that are rapidly turned over by lactic bacteria and yeasts, producing alcohol and lactic acid, which suppress the growth of potentially hazardous bacteria and fungi. In contrast, meat and fish contain very little carbohydrates. Milk as an animal derived product is an exception that is readily susceptible to lactic fermentation. Fermentation of meat can be a risky business due to pathogenic microorganisms that may produce dangerous toxins, in particular when these organisms get access to the interior of the meat that in the living state is sterile.

Fermentation of meat therefore usually involves pre-treatment by salt and application of drying or smoking techniques. In the case of fish, halotolerant visceral enzymes along with various aerobic and anaerobic salt-loving bacteria are able to ferment the pre-treated flesh and prevent putrefying bacteria to get into action. In this case, it is basically a principle of establishing conditions that selects the desirable bacterial and fungal cultures.

Whereas there is a substantial literature about fermentation of plants and plant materials (Katz, 2012), meat (Ockerman and Basu, 2008), as well as fish (Lopetcharat et al., 2007), there is very little published in the scientific literature about insects and in particular fermented insects as foodstuff (van Huis et al., 2014). In the present paper we describe an experimental attempt to produce a gastronomically acceptable fermented sauce from grasshoppers and wax moth larvae and deliver some of the first chemical analysis of insects sauces, combined with the first detailed sensory analysis of them. In the context of the Western cuisine, the particular combination of fermentation and insects represent an ultimate example of the challenging and less edible corner of Lévy-Strauss’ culinary triangle.

In this paper we shall focus on the flavour of the fermented sauces, in particular from taste components derived from proteins and nucleic acids. Being large molecules, proteins and nucleic acids have no taste of their own since they cannot be detected by the taste receptors. Only when broken down into smaller constituents, in particular free amino acids and free nucleotides, respectively, can they stimulate appropriate taste receptors, such as the umami receptor (Mouritsen and Khandelia, 2012). In certain cases, small peptides can also elicit taste, e.g., kokumi taste by the tripeptide glutathione (Maruyama et al., 2012; Kuroda et al., 2012). During fermentation, the proteins and nucleic acids in the raw materials are subject to degradation, and large amounts of free amino acids and nucleotides can potentially be formed. However, the temporal evolution of the contents of these compounds is often highly complex and may be non-monotonic because the produced free nucleotides and amino acids may be consumed at a later stage in the fermentation process, which is the case in beer production. Similarly, high levels of free inosinate in fresh fish may be diminished by postmortem autolytic decay and vanish almost completely during fermentation of fish sauces leading way to less-well tasting compounds, such as inosine or hypoxanthine (Gill, 1990).

Free glutamate and free nucleotides, in particular inosinate, guanylate, and adenylate, enter a unique synergic relation due to an allosteric action on the T1R1/T1R3 umami receptor (Zhang et al., 2008; Mouritsen and Khandelia, 2012). Being highly non-linear, this synergy implies that small amounts of one component, e.g., inosinate, can enhance the sensory perception of glutamate manifold (Yamaguchi and Ninomiya, 2000). This pairing of food items is hence based on a scientific principle in contrast to the claimed food pairing principle based on chemical identity, a principle that proven to be based on culture rather than a scientific principle (Ahn et al., 2011). The proposal of umami as a fifth basic taste (Ikeda, 2002) was based on the finding of large amounts of free glutamate in the brown algae konbu used for production of the Japanese soup stock dashi (Ninomiya, 1998;

Yoshida, 1998). The synergetic action and the umami-pairing principle in traditional dashi are mediated by inosinate from a fish product, katsuobushi, and in vegetarian shōjin dashi by guanylate from dried shiitake. The umami-pairing principle behind the delicious flavour of dashi is the same that is operative in the well-known combinations of foodstuff in the Western cuisine, e.g., eggs-bacon, cheese-ham, and vegetables-meat (Mouritsen et al., 2012; Mouritsen and Styrbæk, 2014).

Only few types of foodstuffs, most prominently sun ripe tomatoes and nori (from the red macroalga species Pyropia spp.) can alone account for both components in umami synergy, and therefore at least two different ingredients are required. However in many cases, due to the non-linear synergetic action, one of the ingredients can be added in small amounts, e.g., a drop of fish sauce or soy sauce, a bit of anchovy paste, a stench of tomato paste, a crumble of Parmesan, or bit of blueskim cheese.

In principle one would have thought that fermented fish sauces could provide both glutamate and inosinate, because fresh fish like mackerel, anchovies, and sardines contain large amount of inosinate and the subsequent fermentation might produce plenty of glutamate.

However, inosinate is quickly broken down enzymatically soon after the fish is dead (Gill, 1990), and very special preparation techniques, e.g., as perfected in the production of katsuobushi (skipjack tuna) and niboshi (sardines), have to be invoked in order to conserve the inosinate. Alternatively the fish could be cooked, dried, and marinated immediately after catching (Maga, 1983), e.g., for producing anchovy paste. In both cases, however, the proteolytic enzymes that could produce glutamate during subsequent fermentation would be inactivated, rendering a product with only little free glutamate. Hence it appears that fermented fish sauces would foremost be glutamate providers.

Whereas there is a wide range of fermented molluscs (e.g., fermented squid) and shellfish (e.g., shrimp paste and original oyster sauce) sauces in Southeast Asia, fish sauces of various origins are undoubtedly some of the most prevalent popular fermented products in the world cuisine, not least in Asia (Lapsongphon et al., 2015). There is rich cultural history behind fermented fish and shellfish products and how they have developed into modern condiments like soy sauce, English sauce, and ketchup products that no longer contain fish (Mouritsen and Styrbæk, 2014). Although these modern products can contain large contents of free glutamate, traditional fish sauces generally dwarf them.

Seafood, it be fish, shellfish, molluscs, or seaweeds, are known to be good sources of umami-tasting compounds (Komata, 1990) and therefore also a good starting point for producing fermented sauces with a very high potential for umami. Fish is a natural and readily available source for producing fermented sauces (Lopetcharat et al., 2007) because fish contain aggressive endogenous enzymes, e.g., in viscera, such as proteases and nucleases that digest proteins and nucleic acids, respectively. The most important contributor to umami in fish sauces is free glutamate. The content of free glutamate can be very large, close to 1400 mg per 100 g in Japanese ishiri and the Vietnamese nuoc mam tom cha, or a little more than in soy sauce (Yoshida, 1998). In contrast, fish sauces seem to contain very little free nucleotides (Park et al., 2001, Funatsu, 2000a; b). Fish sauces are generally produced with high levels of salt, all the way up to 25%, which is considerably more than the 14–18% found in soy sauce (Yoshida, 1998). The combination of umami compounds and salt works synergistically to enhance the saltiness of fish sauce. The less salty fish sauces typically lead to more flavourful products, since the salt tends to limit the enzymatic activity (Lopetcharat et al., 2007). Similarly, the addition of soy sauce to different foods has been demonstrated to be able to reduce the total salt in some prepared foods with 17–50% without noticeable loss of saltiness (Goh et al., 2011; Kremer et al., 2009).

The outline of the remaining part of the paper is as follows. Since our experimentation with fermented sauces naturally writes itself into the grand tradition of ancient fish sauces, we first briefly review and revisit the tradition of the Roman fish sauce garum and offer a few comments about modern East Asian fish sauces for the sake of later comparison. We then describe our experiments with fermenting sauces of fish, insects, game, and peas, leaving technical details, methods of sensory evaluation, and recipes to the “Materials and Methods” section.

In the first “Result” section we present the result of the chemical analyses of the various fermented sauces, including a series of commercial fish sauces. In the second “Result” section, we describe the results of the sensory evaluation of the various sauces.

Penultimately, the results obtained are discussed in “Discussion” and some comments are offered regarding the gastronomic potential of the fermented sauces, specifically with respect to eliciting umami taste and how this correlates with the chemical composition. The paper is closed  by “Conclusion” and “Discussion” sections.