E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A beverage consisting of the juice of apples roasted over spiced ale. A great day for this drink was the feast of the apple-gathering, called in Irish la mas ubhal, pronounced lammas ool, and corrupted into lambs wool.
The pulpe of the rosted apples, in number foure or five mixed in a wine quart of faire water, laboured together untill it come to be as apples and ale, which we call lambes wool.Johnsons Gerard, p. 1460.