Course:FNH200/Projects/2026/Tai O shrimp paste

Shrimp paste (Chinese: 蝦膏 / 蝦醬; Jyutping: haa1 gou1 / haa1 zoeng3) is a salt-fermented condiment used throughout Cantonese cuisine, produced from small planktonic shrimp of the genus Acetes and salt alone. This article concerns the variety made in Tai O, a stilt-house village on Lantau Island, Hong Kong, where production has fallen from roughly ten factories in the 1960s to approximately two today.

The product is of interest to food science because it is a low-acid, high-protein food that is shelf-stable at ambient temperature despite receiving no thermal process, no refrigeration and no added preservative. Its stability rests almost entirely on the reduction of water activity by salting and sun-drying.

Shrimp paste spread on bamboo trays for sun-drying in Tai O. Image by Nicolas Petit for Zolima CityMag).

History and cultural significance

Tai O developed as a fishing and salt-producing settlement, and shrimp paste emerged as a means for the Tanka boat-dwelling community to preserve a seasonal krill catch using locally produced sea salt.

The industry peaked in the mid-twentieth century. Around ten factories operated in Tai O in the 1960s, and the nearby settlement of Ma Wan produced tens of thousands of kilograms annually; Ma Wan's factories are now derelict, and press reporting indicates approximately two producers remain active in Tai O. The oldest surviving business, Cheng Cheung Hing, was founded in 1920 and is in its third generation of family ownership. Shrimp-paste making was included in Hong Kong's first intangible cultural heritage inventory of 480 items, announced in June 2014.

The product reached Canada through migration. Tai O paste was exported to Chinatowns in London, San Francisco and Vancouver, with Taishanese immigrant communities in North America forming a significant market, particularly for steamed minced pork cakes seasoned with salted shrimp.

Production

Acetes krill are washed, mixed with coarse salt, ground to a paste, fermented in open vats for approximately one to two months, then spread thinly on bamboo trays and sun-dried, with the trays turned regularly before the paste is reground and packed.

The drying stage follows standard dehydration principles. Spreading the paste thinly maximises the surface-area-to-volume ratio, while ambient temperature and air movement drive moisture removal and high humidity slows it. Because producers cannot control the weather, they compensate using the only variable available to them: one Tai O maker has described adding several extra pounds of salt when rain is forecast, then blending that batch with a fair-weather batch to even out the final flavour. The same producer reports that his family reduced the recipe's salt level in the late 1990s following public health reporting on sodium.

Fermentation is spontaneous rather than inoculated. No starter culture is added, and the microbial population derives from the shrimp and the salt themselves. Sequencing studies of comparable Asian shrimp pastes identify the halophilic lactic acid bacterium Tetragenococcus as a dominant genus, alongside other salt-tolerant taxa.

Preservation science

Water activity as the controlling hurdle

Published analyses of comparable Southeast Asian shrimp pastes report water activity between 0.63 and 0.74, with salt at roughly 13–17 g per 100 g. Most bacteria require a water activity above approximately 0.90 and most moulds above approximately 0.80; only halophilic bacteria, xerophilic moulds and osmophilic yeasts grow below 0.75. Shrimp paste therefore sits below the threshold for the great majority of spoilage and pathogenic organisms while remaining hospitable to the halotolerant population that carries out the fermentation.

Two hurdles act in combination: salt binds free water osmotically, and sun-drying removes water directly. Neither destroys microorganisms. Salting and dehydration suppress microbial growth rather than eliminate it, so surviving organisms remain viable and can resume activity if the product is rehydrated or diluted.

A low-acid food without a thermal process

Shrimp paste has a pH of approximately 6.8–7.7. It is therefore a low-acid food, well above the pH 4.6 boundary that separates foods in which Clostridium botulinum cannot grow from those requiring a full sterilising process. Shelf-stable low-acid foods are normally made safe by thermal processing. Shrimp paste substitutes a single non-thermal hurdle for that entire process, which is why the salt concentration is not a matter of taste alone.

Flavour and colour development

Endogenous shrimp proteases and enzymes from halophilic bacteria hydrolyse muscle protein into peptides and free amino acids. Liberated glutamate produces the paste's umami intensity, and the accumulating free amino acids also supply reactants for non-enzymatic browning during the long, warm maturation, contributing to the characteristic purple-brown colour.

Safety and nutritional considerations

Biogenic amines. The proteolysis that generates flavour also supplies substrate for bacterial decarboxylases, producing biogenic amines including histamine, cadaverine and putrescine. Studies of Chinese shrimp pastes have found levels not consistently within recommended limits, against a suggested reference threshold of 50 mg/kg for histamine in fish. Biogenic amines are heat-stable, so cooking does not remove them. The evidence is not uniform: a study of Acetes paste fermented at 5–15% salt for 30 days detected no histamine and very low total plate counts, indicating that adequate salt and sufficient fermentation time can control amine formation effectively.

Sodium. At 13–17% salt the product is high in sodium. Low-salt reformulation is an active research area, complicated by the fact that reducing salt alters the microbial community on which the preservation system depends.

Additives. Traditional Tai O paste contains no substance added for preservation, colour or texture, and so falls outside the regulatory definition of a food containing additives. Its stability is a consequence of processing alone.

Comparison with salted fish. A related product of the same villages shows that traditional salt preservation is not uniformly benign. Chinese-style salted fish is classified by the IARC as a Group 1 carcinogen on the basis of its association with nasopharyngeal carcinoma, with N-nitroso compounds as the proposed mechanism. This classification applies to salted fish and has not been extended to shrimp paste.

Regulation of imported shrimp paste in Canada

Canadian oversight is divided between two statutes. Composition and labelling standards fall under the Food and Drugs Act and its regulations, administered by Health Canada. Crustaceans are a priority allergen and must be declared either by common name in the list of ingredients or in a "Contains" statement immediately following it. Because Acetes krill are the sole protein source, this declaration cannot be omitted.

Enforcement and import control fall under the Safe Food for Canadians Act and its regulations, administered by the Canadian Food Inspection Agency. Importers of fish and seafood require a Safe Food for Canadians licence, a written preventive control plan and traceability records, and CFIA seafood surveillance samples for chemical residues, microbiological contamination, allergens and additives.

The below picture is an example of a commercially available shrimp paste product sold in Canada. The label identifies fermented shrimp and salt as ingredients and provides nutrition and product information. This product is not Tai O shrimp paste and is included only as an example of Canadian retail labelling.

Back label of a commercially available shrimp paste sold in Canada, showing the ingredient list and the crustacean allergen declaration required under the Food and Drug Regulations.

Decline and competing pressures

Hong Kong prohibited trawling, including shrimp trawling, in its waters under the Fisheries Protection Ordinance (Cap. 171) with effect from 31 December 2012, across approximately 1,700 km² of territorial waters.

The measure has documented ecological benefits: post-ban surveys recorded large increases in predatory crab densities in both eastern and western Hong Kong waters. It also removed the local krill supply. At least one Tai O producer responded by relocating early-stage production to Yangjiang and Taishan in Guangdong while retaining final processing in Tai O, prompting commentary on whether a paste made from non-local shrimp and processed largely off-site remains a Hong Kong product.

Cheaper factory-made paste from mainland China and Southeast Asia has displaced Tai O producers in their home market while keeping the condiment affordable and widely available. Reporting attributes the remaining decline chiefly to an absence of successors willing to enter the trade.

Proposed final examination question

Question: Tai O shrimp paste has a pH of approximately 6.8–7.7, contains no preservative other than salt, and is never heat-processed, yet it remains shelf-stable at ambient temperature for years. Which option best explains this?

A. The paste is an acid food, so Clostridium botulinum cannot grow in it and no further preservation is needed.

B. Salting and sun-drying reduce water activity below the level most microorganisms require, substituting for the thermal process a low-acid food would normally need.

C. Fermentation generates enough lactic acid to render the paste commercially sterile, destroying the microorganisms present.

D. Sun-drying heats the paste sufficiently to inactivate vegetative cells and spores, achieving the same result as commercial sterilization.

Correct answer: B

Explanation: At pH 6.8–7.7 the paste is a low-acid food, above the pH 4.6 boundary, so option A misstates the pH. Salting and sun-drying lower water activity to roughly 0.63–0.74, below the level required by most spoilage organisms and vegetative pathogens, leaving only halophilic and halotolerant organisms able to grow. Options C and D share a single misconception: that the preservation step destroys the microbial population. It does not. Salting, drying and fermentation suppress microbial growth rather than eliminate it, and the surviving organisms remain metabolically active — which is why proteolysis continues throughout maturation and heat-stable biogenic amines such as histamine can accumulate in a product that is nonetheless shelf-stable.

This question should be included on the FNH 200 final exam because it requires students to transfer the water activity and pH 4.6 concepts to an unfamiliar food rather than recall a lecture example, and because all three distractors test the same widespread error of treating "preserved", "unspoiled" and "safe" as the same property. That distinction generalises well beyond this product, to salted fish, cured meats and fermented sauces.

See also

• Bagoong (FNH 200, 2022) — a Filipino fermented shrimp and fish product differing in raw material, salt ratio and maturation
• Slow Food Foundation — Ark of Taste