Lemon and orange extract can both be made quite easily in your kitchen. It uses the concept of extraction to preserve and concentrate that flavour!
DIY Orange Extract Recipe with 200 Proof Alcohol A Culinary Guide for Home Cooks and Chefs – Culinary Solvent
Unveiling the Secrets: How Long Does Orange Extract Last?
The Science of Making Paneer + How To Guide, Recipe
DIY Lemon Extract - The Coconut Mama
Easy Homemade Orange Extract for Baking & More
How to Make Orange Extract + Free Labels - Tidbits
3 Ways to Extract Oil from Orange Peels - wikiHow
Homemade Citrus Extracts - Spoonful of Flavor
Insights into the chemical composition and bioactivities of citrus peel essential oils - ScienceDirect
The Zesty History: The Use of Ethanol in Making Citrus Extracts – Culinary Solvent