Understanding Food: Fish and Shellfish

Understanding Food: Principles & Preparation - Fish and Shellfish

Overview of Seafood

  • Source of Sustenance: Seafood is an essential food source and offers sustenance.

  • Species Diversity: Approximately 20,000 known species of seafood exist.

  • Hunting and Consumption: Seafood remains one of the major food sources actively hunted, with millions of tons consumed annually.

  • Classification: Seafood can be classified into three categories:
      - Based on biology: Vertebrate or invertebrate.
      - Based on fat content: Lean or fat.
      - Based on habitat: Saltwater or freshwater.

Classification of Fish and Shellfish

1. Vertebrate or Invertebrate

  • Vertebrate: Fish with fins and internal skeletons that obtain oxygen from water. Types include:
      - Finfish: These possess fins (e.g., salmon, cod).
      - Sea Mammals: Such as whales and dolphins that obtain oxygen from the air.

2. Shellfish (Invertebrates)

  • Defined as creatures with external skeletons or shells. Categories include:
      - Crustaceans: Such as shrimp and crabs.
      - Mollusks: Include:
        - Univalve: One shell (e.g., snails).
        - Bivalve: Two hinged shells (e.g., clams, oysters).
        - Cephalopods: E.g., squid and octopus.

3. Habitat: Salt or Freshwater

  • Saltwater Fish: Notably have a distinct flavor, with examples being:
      - Halibut, flounder, tuna, salmon, swordfish, shark.

  • Freshwater Fish: Examples include:
      - Catfish, trout, tilapia, pike.

Detailed Fish and Shellfish Classification

Fish Types

  • Finfish: Divided into fresh and saltwater.

  • Shellfish: Further categorized into crustaceans and mollusks.

Tables of Common Fish and Shellfish by Flavor and Texture

  • Flavor:
      - Mild Flavor: Cod, flounder, mussels.
      - Moderate Flavor: Lobster, mullet, salmon.
      - Full Flavor: Tuna, swordfish, mackerel.

  • Texture:
      - Delicate: Cod, whitefish.
      - Firm: Tuna, sturgeon.

Fat Content of Fish

  • Lean Fish:
      - Less than 2.5 grams of total fat (e.g., cod, haddock).

  • Low Fat: 2.5 - 5 grams total fat (e.g., catfish, trout).

  • Moderate Fat: 5 - 10 grams total fat (e.g., salmon, herring).

  • High Fat: More than 10 grams total fat (e.g., mackerel, salmon king).

Structure and Properties of Finfish

  • Tenderness Factors:
      - Collagen Content: Low (3% content) which converts to jelly at low temperatures.
      - Muscle Structure: Consists of short fibers and distinct layers: myotomes and myocommata, crucial for the characteristic flakiness.

Connective Tissues

  • Myosepta: Layers of collagen connecting myotomes offering structural character.

Pigmentation in Fish

  • White vs. Colored Flesh: Darker pigments indicate slow-twitch muscle fibers (used for endurance) while lighter indicates fast-twitch fibers (used for sprinting).

  • Myoglobin Levels: More myoglobin correlates with darker flesh and higher oxygen storage capacity.

Perishability Factors in Fish

  • Fish flesh is more perishable, influenced by:
      - Tissue Components: Based on hunting methods (sea vs. freshwater).
      - Post-Harvest Handling: Affects freshness and spoilage.
      - Rigor Mortis: The stiffening that occurs after death leading to spoilage.

  • Trimethylamine Oxide (TMAO): A natural compound found in fish that breaks down to TMA leading to spoilage odors.

Purchasing Fish & Shellfish

Types and Uses

  • Finfish and Shellfish Types: Common seafood options and their culinary uses listed.

  • Selection Criteria: Freshness indicators such as firm flesh, tight scales, red gills, and bright eyes.

  • Packaging Forms: Fish can be bought whole, dressed, filleted, or canned.
      - Examples: Tuna - “white” from albacore, “light” tuna includes all non-albacore types.

Sustainability and Ethics

  • Caution regarding mercury levels in fish:
      - Low Mercury Fish: Salmon, shrimp, catfish.
      - Moderate Mercury Fish: Canned tuna, halibut.
      - High Mercury Fish: Shark, swordfish.

  • Guidance for pregnant women on safe seafood consumption to avoid mercury exposure.

Shellfish Selection and Purchasing

  • Shellfish should be purchased live when possible. Notable points:
      - Lobsters, Crabs, Oysters, Clams: Key freshness indicators (e.g., closed shells).
      - Soft-Shelled vs. Hard-Shelled Clams: Differences in texture and preparation outcomes.

Specific Considerations for Shellfish

  • Mussels: Should remain in their shells until cooking.

  • Shrimp: Sold in multiple forms, suggested portion size indicated.

  • Crabs: Students are taught to recognize male and female distinctions based on anatomy for better meat yield.

Nutritional Analysis of Seafood

  • Protein Content: High biological value proteins in fish, responsible for umami taste.

  • Carbohydrates: Naturally low, with glycogen contributing a sweetish taste in shellfish.

  • Fats: Emphasis on omega-3 fatty acids health benefits.

Grading Seafood

  • Inspection and Grading: Seafood graded based on various qualities including freshness, appearance, and odor.

Certification Issues

  • Shellfish certification from inspected waters is crucial for safety and health. "Sell by" dates necessary for shucked shellfish confirmation.