The lemon is both a small evergreen tree (Citrus × limon, often given as C. limon) native to Asia and the tree’s oval yellow fruit. The fruit is used for culinary and nonculinary purposes throughout the world – primarily for its juice, though the pulp and rind (zest) are also used, mainly in cooking and baking. Lemon juice is about 5% to 6% (approximately 0.3 Molar) citric acid, which gives lemons a sour taste, and a pH of 2 to 3. This makes lemon juice an inexpensive, readily available acid for use in educational science experiments. Many lemon-flavored drinks and candies are available, including lemonade and lemonheads.
Lemon juice, rind, and zest are used in a wide variety of culinary applications:
- Lemon juice is used to make lemonade, in soft drinks, and as a marinade for both fish, where its acid neutralizes amines in fish by converting them into nonvolatile ammonium salts, and meat, where the acid partially hydrolyzes tough collagen fibers tenderizing the meat.
- Lemon juice is also used as a short-term preservative on certain foods that tend to oxidize and turn brown after being sliced, such as apples, bananas and avocados, where its acid denatures the enzymes which cause browning and degradation. Lemon juice and rind are used to make marmalade and lemon liqueur.
- Lemon slices and lemon rind are used a garnish for both food and drinks.
- Lemon zest, the grated rind of the fruit, is used to add flavor to baked goods, puddings, rice and other dishes.
- Pickled lemons are a Moroccan delicacy.
- Citric acid – Lemons were the primary commercial source of this substance prior to the development of fermentation-based processes.
- Lemon battery – A popular science experiment in schools involves attaching electrodes to a lemon and using it as a battery to produce electricity. Although very low power, several lemons used in this way can power a small digital watch. These experiments also work with other fruits and vegetables.
- Sanitary kitchen deodorizer – deodorize, remove grease, bleach stains, and disinfect; when mixed with baking soda, lemon juice can remove stains from plastic food storage containers.
- Insecticide – The d-limonene in lemon oil is used as a non-toxic insecticide treatment. See orange oil.
- Antibacterial uses because it has a low pH
- Wood treatment – lemon oil is used in both wood cleaner and polish, where the solvent property of d-limonene is employed to dissolve old wax, fingerprints, and grime.
- A halved lemon is used as a finger moistener for those counting large amounts of bills such as tellers and cashiers.
- Aromatherapy – In one of the most comprehensive scientific investigations done yet, researchers at The Ohio State University reveal that lemon oil aroma does not influence the human immune system but may enhance mood.
- A halved lemon dipped in salt or baking powder can be used to brighten copper cookware. The acid cuts through the tarnish and the abrasives assist the cleaning.
- Lemon juice may also be used to lighten hair color.