eggeskall

Eggshell, known in Norwegian as eggeskall, is the hard outer covering of an egg. It protects the contents, provides structural support, and helps regulate moisture and gas exchange. Most eggshell is primarily calcium carbonate, with a thin organic matrix and a specialized outer coating called the bloom that reduces water loss and resists microbial intrusion.

Composition and structure: An eggshell is about 95 percent calcium carbonate, with the remainder consisting of organic proteins and trace minerals. The shell has an inner calcified layer and an outer cuticle, plus membranes close to the egg’s contents. Its porosity allows limited gas exchange while helping to prevent rapid dehydration; pore structure and thickness vary by species and age.

Formation: Eggshell formation occurs in the oviduct, where the shell gland deposits layers of calcium carbonate around the albumen and membranes. The process takes roughly a day. Diet, age, and species influence shell thickness and strength, while pigments can affect shell color in some birds.

Functions and uses: The shell serves as physical protection and a barrier to pathogens, while the pores enable necessary gas exchange for the developing or stored contents. In agriculture and gardening, ground eggshells are used as a calcium source and soil amendment, potentially helping to raise pH and supply calcium to plants and poultry. In culinary and home contexts, dried eggshell powder is used as a calcium supplement or fortification, provided it is cleaned, sterilized, and ground to a fine powder to avoid sharp particles.

Safety and disposal: Raw eggshells can harbor bacteria such as Salmonella, so they should be rinsed and, if reused, sanitized (e.g., by drying or heating) before grinding or composting. Eggshells are widely compostable and can contribute to kitchen waste reduction.