Although the colonists of seventeenth- and early-eighteenth-century British North America consumed most of the grain produced in the colonial economy, few households were self-sufficient. Instead, they traded with their neighbors for what they did not produce themselves. In any given year, farmers who produced more grain than they needed would exchange their surpluses locally with other farmers who had different surpluses, with local laborers who supported themselves by selling their labor, or with the local storekeeper, who might also be the miller (trade person who ground grain into flour). Satisfying the domestic demand for bread stuff, then, depended on trade between neighbors. The colonists recorded these myriad transactions as credits and debts in their individual account books. Debts and credits could remain outstanding for years before being settled. Trading based on book credit gave more value to maintaining equilibrium between local supply and demand and to preserving a cooperative spirit among neighbors than to expanding production beyond the immediate needs of the locality. Colonists also traded grain surpluses long-distance, responding to impersonal demand beyond the community. Some of the long-distance trade catered to regional and urban domestic demand. As the urban areas matured, they increasingly relied on producers in distant areas for grain and other agricultural supplies. In the early 1750s, the most densely populated towns of eastern and southern New England had begun importing substantial quantities of flour and rice from the middle and southern colonies to compensate for grain deficits that developed in their region. Other urban areas followed their example, though their greater proximity to grain regions enabled them to tap supplies closer to home. Assuming that in the early 1770s at least half of the demand for grain from farmers with surpluses was satisfied through long-distance channels, the proportion of grain produced for consumption beyond the local market probably accounted for about a quarter of total grain production consumed by humans. The colonists organized the long-distance grain economy differently from their local economy. New mechanisms enabled the long-distance economy to respond sensitively to variations in demand, and these in turn gave it greater dynamism than the community-centered, local economy possessed. The contrast between the local and long-distance grain trade is best illustrated by looking at the flour-milling industryflour-milling industry. Nearly every area of colonial settlement had a local gristmill to which farmers brought grain to be custom ground. The limited capital value of most custom mills, the need to process rye and corn as well as wheat, together with seasonal factors affecting the water supply, restricted the volume of wheat flour that could be produced. The production of flour for long-distance exchange and particularly for export usually took place in merchant mills that were larger, had more capital, and were increasingly specialized. The difference between a merchant mill and a custom mill was one of degree as much as kind. Most merchant mills had started as custom mills, and the colonial and state governments often compelled merchant mills to set aside certain days for custom work. Mills that acquired the designation "merchant" did so because they catered to the demand of merchants in the principal ports. These merchants enabled certain millers to specialize in wheat flour by placing orders for large parcels of it and paying in cash. That in turn allowed the millers to offer cash to the primary producers and grain brokers who delivered wheat to their mills. Cash was the economic motivator of this export-oriented economy for the simple reason that farmers would prepare and haul their grain to landings and mills and even increase their wheat acreage to obtain this commodity. Cash gave farmers choices they did not enjoy when they traded with neighbors alone. Beyond opening up access to a range of products that could not be produced locally, it freed them from the web of mutual indebtedness and allowed more choices in the selection of trading partners. In other words, the cash economy allowed producers to seek the best bargains in that wider, impersonal market of which the export of agricultural surpluses formed the principal part. Of course, few in this age would have welcomed total release from the support and obligations that local trade conferred.