Lemon essential oil is extracted from porous and aromatic fruit's rinds in different ways:

By hand using a Sponge Extraction Process (now abandoned)

Basically, lemons are halved transversely, then the peel is pressed against a sponge, so that the oil-glands burst open and the sponge absorbs the exuded oil, which is collected in a receiving vessel.
Due to market and economy demands, today are preferred mechanical techniques, although the so-extracted juice is of an excellent quality.

Through a Cold Press Extraction (by grinding or rasping)

Lemons are placed in devices, called Sfumatrici, which screw and scrape lemon's rind and therefore essence pour out from the oil cells. This technique allows the production of a very good quality essential oil (since thermal treatments do not compromise the terpenic mix), even though the amount of oil extracted is scarce. Thanks to this system is extracted also some water, that will be separate by centrifugation.

Another technique in use is the hydraulic press: lemons are minced and the melted staff, draining from the press, is steam-distilled with low pressure. What left from centrifugation and distillation can be useful to produce citric acid or calcium citrate.

The worthily-quality deterpenic essential oil, with a perfume 15 times finer than a standard essential oil, is obviously more expensive. The oil that has been deterpened, which is to say, that its terpens by distillation (deterpenization) has been removed, can be used to extract vacuum-packed solvent for cosmetic and food.

The greasy liquid extracted - yellowish, citrus scented and with a citrate taste along with a bitter and sour aftertaste - is alcohol soluble and it's made of limonene (or terpene). Among all the other components: Camphene, Pinene, Phellandrene, Terpinenes, Cymene, Monoterpenes, Alkanes, Aldehydes (Citral, Geranial), Coumarine and Furanocoumarine.

Technical report

Main components: Limonene (60-69%), Linalil and Geranil Acetates, Terpinene, Sabinene, Pinene, Citral, Linalool, Octanol, Citronellal, Bergamoten, Nonalool, Mycenae, Iron, Calcium, Silicon, Phosphorus, Copper, Manganese, Vitamins (B1, B2, B3, To, C).

Extraction: Cold press extraction
Balsamic period: spring
Essence profit: 0,3-0,5
Smell intensity: 4
Density: 0,85- 0,86

Uses

Lemon essential oil is widely employed by food, pharmaceutical and cosmetic industries as food, beverage, liquors, drugs and perfumes flavourer.

Curiosity

To collect only a kilo of lemon essential oil, we need about 200 kg of lemons (almost 1500-2000 lemons). That's why this kind of oil is so precious and expensive. The more valuable quality of lemon essences is extracted by unripe fruits (i.e. in Italy the most precious quality essence are made with lemon yielded and used from the end of November to the early begin of March in Ionian area, whereas, in Sicily, until all April month. After this period the quality standard decreases).