Existing contracts with Starbucks, Nestle, others honored By Gustavo Bonato Reuters August 6, 2012 SAO PAULO, Aug 6 (Reuters) - Brazil's Cooxupe, the world's largest coffee co-operative, said on Monday that it would halt new spot export business until September, when the current harvest is over and it has a better sense of the supply of top-quality arabica beans. Top-quality arabica beans would only make up about 56 percent of Brazil's total 2012/13 arabica crop due to untimely rains during the harvest period, down from 80 percent in past crops, said Joaquim Libânio Ferreira Leite, Cooxupe's head of sales. "Our house has a reputation for producers of very fine coffees. I can't promise my clients something and tomorrow frustrate them by not delivering," said Leite at an agricultural seminar in Sao Paulo. He said the co-op would continue to deliver on its long-term contracts to buyers such as Starbucks Corp and Nestle SA but s...