Species, breeds, and sex used Geese Traditionally, foie gras was produced from special breeds of geese. However, by 2004, geese accounted for less than 10% of the total global foie gras production and by 2014 only 5% of total French production. Goose breeds used in modern foie gras production are primarily the grey Landes goose (
Anser anser) In 2016, Hungary was producing 80% of the world's goose foie gras; however, production rates are likely to drop in 2017 due to outbreaks of bird flu.
Ducks In 2014, ducks accounted for 95% of foie gras production. This new method should replace the slaughter of females after hatching within a few years.
Physiological basis The basis of foie gras production is the ability that some
waterfowl have to expand their esophagus and to gain weight, particularly in the liver, in preparation for migration. Wild geese may consume 300 grams of protein and another 800 grams of grasses per day. Farmed geese allowed to graze on carrots adapt to eating 100 grams of protein but may consume up to 2500 grams of carrots per day. The increasing amount of feed given before force-feeding and during the force-feeding itself cause the expansion of the lower part of the esophagus. • The third stage ("pre-fattening") lasts from 63 to 81 days of age (9–12 weeks). The birds are brought inside for gradually longer periods while introduced to a high-starch diet. This is a feeding transition where the food is distributed by meals, first in restricted amounts and time and, after that, greatly increased.
Feeding phase The next production phase, which the French call or , or "completion of fattening", involves forced daily ingestion of controlled amounts of feed for 10 to 12 days) and 15 to 18 days with geese. During this phase, ducks are usually fed twice daily, while geese are usually fed three times daily. To facilitate the handling of ducks during gavage, these birds are housed throughout this phase in one of the following systems: • Elevated collective cages indoor • Elevated collective pens indoor • Ground pens indoor Individual cages ("épinettes" in French) have been banned in Europe. Typical foie gras production involves force-feeding birds more food than they would eat in the wild, and much more than they would voluntarily eat domestically. In modern production, the bird is typically fed a controlled amount of feed, depending on the stage of the fattening process, the bird's weight, and the amount of feed the bird last ingested. At the start of production, a bird might be fed a dry weight of of food per day and up to (in dry weight) by the end of the process. The actual amount of food force-fed is much greater because water is added to the dry feed. For pellets, the typical composition is about 53% dry and 47% liquid (by weight). This is the equivalent of around 1,900 grams per day in total mass. For whole grain, the cooked weight is about 1.4 times the dry weight. The feed is administered using a funnel fitted with a long metal or plastic tube (20–30 cm long), which forces the feed into the bird's esophagus. If an
auger is used, the feeding takes about 45 to 60 seconds, however, modern systems usually use a tube fed by a pneumatic pump with an operation time of 2 to 3 seconds per duck. During feeding, efforts are made to avoid damaging the bird's esophagus, which could cause injury or death, although researchers have found evidence of inflammation of the walls of the proventriculus after the first session of force-feeding. There is also an indication of inflammation of the esophagus in the later stages of fattening. Several studies have also demonstrated that mortality rates can be significantly elevated during the gavage period. The feed, usually corn boiled with fat (to facilitate ingestion), deposits large amounts of fat in the liver, thereby producing the buttery consistency sought by some
gastronomes. Ducks reared for foie gras are typically slaughtered at 100 days of age, although modern production methods with shortened pre-feeding and force feeding phases allow for an earlier slaughter, around 93 days. Storage of fat in the liver produces
steatosis of the liver cells.
Alternative production Ethical concerns have driven a recent interest in alternative production methods that produce fattened liver without gavage, and, , at least 16 producers offered a meat-based foie gras alternative. in part because substitutes for gavage do not produce the same results. The current method, developed in
Extremadura, Spain, involves timing the slaughter to coincide with the winter migration, when the livers naturally fatten. Prior to slaughter, the birds are allowed to eat freely, termed . For this innovation, the producer,
Patería de Sousa, won the award at the 2006. Because gavage fattens goose livers to substantially larger than their natural size, de Sousa's technique is less
efficient at producing a fixed
mass of foie gras, and composes a small fraction of the market. To achieve similar efficiency per mass to gavage, the British supermarket chain
Waitrose sells a product which it calls (but see ), made from free-range British goose or duck liver blended with additional fat. Subsequently, researchers at the German and the company GMT developed
a process to apply additional fat to duck
liver meat at
high pressure. Even trained chefs struggle to distinguish the result from traditional foie gras. More radical approaches are possible. A duck or goose with damaged
ventromedial nucleus in the hypothalamus will feel less satiety after eating and therefore eat more. In
lesioning experiments, this effect more than doubled the bird's food consumption. Alternatively,
human microbiome studies on
obesity led French researchers at
Aviwell develop a probiotic preparation that produces fatty livers in geese over six months without gavage.
Vegan alternatives A Spanish company began selling a vegan alternative to
foie gras called Fuah, in 2022. The product is made from
cashew nuts, coconut oil, and
beetroot. The American product
Faux Gras is a vegan, nut-based spread. In , an animal welfare non-governmental organization found at least 14 producers of vegetarian or vegan alternatives to
foie gras. ==Preparations==