Poire William is a French colourless Eau de Vie (brandy) made with the Williams' Bon Chrétien pear which is nowadays commonly called the Williams pear, or Bartlett pear. The Williams pear is thought to date from 1765 to 1770 from the yard of an Aldermaston, England schoolmaster – it may have been related to the older French pear the Bon Chrétian. A nurseryman named Williams later acquired the variety, and after introducing it to the rest of England, the pear took his name.
Poire Williams is generally served chilled as an after-dinner drink and many producers include an entire pear inside each bottle – this is sometimes known as Poire Prisonnière (Prisoner Pear). This is achieved by attaching the bottle to a budding pear tree so that the pear will grow inside it. This is a technique going back hundreds of years in which the bottle is placed over the developing fruit bud on the tree. The neck of the bottle is hung downwards to prevent rainwater from running into it. The pear grows and ripens and is harvested, complete with bottle, between late August and early September. The bottles are are then filled with brandy for the fruit to absorb with the brandy being topped up till the pear is saturated. The bottle is then filled with eau de vie de Poire William without any risk of seeing the level drop through absorption by the fruit.