In early times, the pea was grown mostly for its dry seeds. In modern times, however, peas are usually boiled or steamed, which breaks down the cell walls and makes the taste sweeter and the nutrients more bio-available. Along with broad beans and lentils, these formed an important part of the diet of most people in Europe during the Middle Ages (Bianchini 1975 p 40). By the 1600s and 1700s it had become popular to eat peas "green", that is, while they are immature and right after they are picked. This was especially true in France and England, where the eating of green peas was said to be "both a fashion and a madness" (OSU 2006). New cultivars of peas were developed by the English during this time which became known as the garden pea and English pea. The popularity of green peas spread to North America. Thomas Jefferson grew more than 30 cultivars of peas on his estate (Kafka 2005 p 297). With the invention of canning and freezing of foods, green peas became available year-round, and not just in the spring as before.