ACE stands for Additionnal Cask Enhancement, according to the Laddie's semantics.
Malmsey is a noble variety grown in Madeira where it is also known as Malvasia Candida. It was the first of the noble varieties to be planted in Madeira back in the 16th century.
It is a high yielding, late ripening grape which performs best on well-drained soils and in well-sheltered low altitude sites. It is often blended with Tinta Negra Mole in the production of Malmsey which is the island's richest and sweetest wine.