Allergen guide

Shellfish in recipes — how Frittu checks and excludes it

Shellfish is one of the most widely distributed allergens in world cooking — and one of the most hidden. Fermented condiments, processed seafood products, and background flavouring pastes can all introduce shellfish into a recipe without the word “shellfish” ever appearing. This page explains what Frittu's system does, specifically, when shellfish is listed as an excluded ingredient in a user's profile.

Shellfish in everyday cooking

Shellfish covers two distinct groups in food allergy contexts. Crustaceans include prawns, shrimp, crab, lobster, crayfish, and similar species. Molluscs include scallops, mussels, clams, oysters, squid, calamari, and octopus. Cephalopods such as squid and octopus are classified as molluscs, placing them in the shellfish category for allergen purposes even though they look and cook quite differently from prawns or clams.

What makes shellfish challenging from an ingredient-awareness perspective is not the whole-animal forms — a prawn on a plate is identifiable — but the fermented, dried, and processed derivatives that function as background flavouring agents. A Thai curry paste may list kapi as a base ingredient. A Malaysian sambal is built on a rempah of belacan. A Chinese stir-fry marinade typically calls for oyster sauce. A California roll contains surimi — imitation crab made with shellfish extracts. In each case, the finished dish name gives little indication that shellfish is present.

Dried shrimp present a similar challenge. They are small, intensely flavoured, and used as a seasoning ingredient in Southeast Asian, Chinese, and Latin American cooking. They dissolve into dishes during cooking, contributing depth rather than a distinct shellfish taste — which is why a recipe might list them under a generic seasoning step without signalling their shellfish origin.

How Frittu's allergen check works

When your profile lists shellfish as an excluded ingredient, Frittu applies a two-layer check to every recipe it generates.

Layer 1 — prompt-side instruction.Before sending a generation request to Claude, Frittu builds an exclusion list from your allergen profile. For shellfish, that list includes not just “prawn” and “shrimp” but also the fermented pastes, processed derivatives, and culinary aliases most likely to appear in a recipe: oyster sauce, shrimp paste, prawn paste, belacan, blachan, balachan, kapi, bagoong, ebi, dried shrimp, surimi, imitation crab, squid, calamari, and octopus. Claude receives these as a hard exclusion instruction and is directed to build the recipe without them.

Layer 2 — deterministic post-generation scan.After the recipe is returned, Frittu runs a server-side function that checks every ingredient name against a coded keyword list for shellfish. Short regional ingredient names like “kapi” are matched as whole words so they do not produce false matches on longer words that contain the same letters. If a recipe still contains a matched keyword after generation, it is rejected and Frittu attempts to generate an alternative before the recipe reaches you.

What this check does not cover. The check operates on ingredient names as generated. It does not cover cross-contamination from shared cooking surfaces, woks, or utensils used for shellfish-containing dishes — a particularly relevant consideration in restaurant-style stir-fry cooking where shellfish and non-shellfish dishes are prepared in the same equipment. It also does not account for ingredients a user adds themselves after receiving the recipe. Standard kitchen precautions remain relevant regardless of what a recipe generator produces.

Hidden sources of shellfish in cooking

Common hidden sources of shellfish in cooking include the following — ingredients that contain shellfish but may appear in a recipe without the word “shellfish” — or even a recognisable shellfish name — being present.

Oyster sauce — Made from concentrated oyster extracts — oysters are bivalve molluscs classified as shellfish. Oyster sauce is one of the most ubiquitous condiments in Chinese cooking, appearing in stir-fries, braised dishes, noodle marinades, and vegetable preparations. The dish name typically gives no indication it is present; it functions as a background umami ingredient.

Shrimp paste / prawn paste — A fermented condiment made from small shrimp or prawns combined with salt. It is used as a flavour base across Thai, Malay, Indonesian, and Vietnamese cooking — often fried into the oil at the start of cooking to build the foundation of a dish. Its flavour blends into the background quickly, making it easy to overlook in a recipe.

Belacan / blachan / balachan — The Malaysian and Singaporean form of fermented shrimp paste, sold in compressed blocks and typically toasted in a dry pan before use. Belacan is a foundational ingredient in rempah spice pastes, laksa, and many sambals. It appears under multiple spellings — belacan, blachan, balachan — all of which are checked.

Kapi — Thai fermented shrimp paste, functionally similar to belacan and used in Thai curry pastes, nam prik dipping sauces, and som tum. Frittu's check matches “kapi” as a standalone ingredient word so that unrelated words containing the same letters are not flagged.

Bagoong — A Filipino fermented condiment that comes in two main forms: fermented shrimp paste (bagoong alamang) and fermented fish paste (bagoong isda). The shrimp form is a critical accompaniment to kare-kare and is used as a seasoning and condiment across Filipino cooking. Both forms are flagged under the “bagoong” keyword.

Ebi — The Japanese word for shrimp, which appears in Japanese recipe ingredient lists where you might otherwise expect the English term. Ebi tempura, ebi furai (breaded fried prawn), and ebi mayo are common preparations. The keyword “ebi” catches these Japanese-language ingredient references.

Dried shrimp — Small sun-dried shrimp used as a seasoning ingredient rather than a primary protein. They are common in Southeast Asian cooking (Thai salads, Malaysian fried rice, Malay kerabu), Chinese cooking (turnip cake, congee, stir-fried greens), and Latin American cooking (Mexican dried shrimp in mole). They dissolve into dishes during cooking, contributing depth without a distinct shellfish taste in the final dish.

Surimi / imitation crab — A processed seafood product made primarily from Alaska pollock that is formed and flavoured to resemble crab or lobster. Despite being a fish-based product, surimi is flavoured using shellfish extracts, meaning it contains shellfish-derived compounds. It is sold as imitation crab, crab sticks, or seafood sticks and is used in California rolls, seafood salads, and some pasta dishes — often without any reference to shellfish in the product name. Frittu's keyword list includes both “surimi” and “imitation crab” as separate entries.

Squid / calamari / octopus — Cephalopods — squid, calamari, and octopus — are classified as molluscs, placing them in the shellfish category for food allergy purposes. They appear across Mediterranean cooking (grilled squid, Spanish pulpo a la gallega), Japanese cooking (takoyaki, ika sashimi), and Southeast Asian cooking. The word “calamari” is the Italian name for squid, commonly used in restaurant menus and recipe names, and is flagged alongside “squid” and “octopus” in Frittu's keyword list.

Frequently asked questions

How does Frittu's system check for shellfish in a generated recipe?

Frittu uses a two-layer process. First, before generating a recipe, Claude is given an exclusion list built from your allergen profile. For shellfish, that list covers whole crustaceans and molluscs as well as their fermented, dried, and processed derivatives — including condiments like oyster sauce and shrimp paste, regional ingredients like belacan and kapi, and processed products like surimi. Claude is instructed to build the recipe without any of those ingredients. After the recipe is returned, a server-side function checks every ingredient name against a coded keyword list for shellfish. Any match causes the recipe to be rejected and Frittu attempts to generate an alternative.

Does oyster sauce trigger the shellfish check?

Yes. Oyster sauce is made from concentrated oyster extracts — oysters being a bivalve mollusc classified as shellfish. It is one of the most widely used condiments in Chinese cooking, appearing in stir-fries, braised dishes, noodle marinades, and vegetable preparations. The dish name typically gives no indication that oyster sauce is present; it is used as a background umami ingredient rather than a prominent flavour note. Frittu's keyword list includes "oyster sauce" directly, so any recipe calling for it is flagged and regenerated when shellfish is excluded from a user's profile.

What is belacan and why is it in the shellfish keyword list?

Belacan — also spelled blachan or balachan — is a Malaysian and Singaporean fermented shrimp paste sold in compressed blocks. It is made by fermenting small shrimp with salt, then sun-drying and pressing the paste. Belacan is a critical background ingredient in rempah spice pastes, laksa, and many Malaysian sambals. It is typically toasted in a dry pan before use, which gives dishes a deep, savoury character without a recognisably "prawn" flavour in the final dish. Because it appears under multiple spellings, Frittu's keyword list includes "belacan," "blachan," and "balachan" as separate entries.

What is surimi and why is it flagged?

Surimi is a processed seafood product typically made from Alaska pollock — a non-shellfish white fish — that is formed and flavoured to resemble crab or lobster meat. Despite being made primarily from fish, surimi is flavoured and coloured using shellfish extracts, which means it contains shellfish-derived compounds. It is sold as "imitation crab," "crab sticks," or "seafood sticks" and used in California rolls, seafood salads, and some pasta dishes. The product name often omits any reference to shellfish, which is why Frittu's keyword list flags both "surimi" and "imitation crab" explicitly.

What happens when a generated recipe triggers the shellfish check?

The recipe is rejected before it is saved or shown to the user. Frittu retries the generation automatically. The rejection and retry happen server-side — the user sees only the final recipe that passed the check. If repeated retries continue to produce a recipe that triggers the check, the generation does not complete.

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