These are wines obtained from a single harvest, forming the basis of a blend of which 10% may be bottled each year. A wine of the same quality is used to fill the cask. Up to 10 additions may be made, after which the remaining wine must all be bottled under the "SOLERA" system. H&H has some examples in considerable quantities.
This process was used in the 19th century when diseases destroyed many vineyards and producers had to use it to obtain enough wine to supply their customers. Today the "Solera" system is no longer used.