of Port, a small amount of distilled alcohol made from cane sugar was added to stabilize the wine by boosting the alcohol content (the modern process of fortification using brandy did not become widespread until the 18th century). The Dutch East India Company became a regular customer, picking up large (112 gal/423 L) casks of wine known as "pipes" for their voyages to India. The intense heat in the holds of the ships had a transforming effect on the wine, as discovered by Madeira producers when one shipment was returned to the island after a long trip. The customer was found to prefer the taste of this style of wine, and Madeira labeled as vinho da roda (wines that have made a round trip) became very popular. Madeira producers found that aging the wine on long sea voyages was very costly, so they began to develop methods on the island to produce the same aged and heated style. They began storing the wines on trestles at the winery or in special rooms known as estufas, where the heat of the island sun would age the wine. The 18th century was the "golden age" for Madeira. The wine's popularity extended from the American colonies and Brazil in the New World to Great Britain, Russia, and Northern Africa. The American colonies, in particular, were enthusiastic customers, consuming as much as 95% of all wine produced on the island each year. Early American history (17th – 18th centuries) Madeira was a very important wine in the history of the United States of America. No wine-quality grapes were grown among the thirteen colonies, so imports were needed, with a great focus on Madeira. One of the major events on the road to the American Revolution in which Madeira played a key role was the British seizure of John Hancock's sloop on 9 May 1768. Hancock's boat was seized after he had unloaded a cargo of 25 pipes () of Madeira, and a dispute arose over import duties. The seizure of Liberty caused riots to erupt among the people of Boston. Madeira was a favorite of Thomas Jefferson, and it was used to toast the Declaration of Independence. George Washington, Alexander Hamilton, Benjamin Franklin and John Adams are also said to have appreciated the qualities of Madeira. The wine was mentioned in Benjamin Franklin's autobiography. On one occasion, Adams wrote to his wife, Abigail, of