The cultivation of sugar cane and the production of sugar largely forged the local and international identity of Puerto Rico until the 20th century. According to historical documents, the first farms producing the sweetener date to the 16th century. These sugar mills were known locally as ingenios or trapiches. In 1523, Genovese native Tomás de Castellón established in San Germán the first sugar mill, called San Juan de las Palmas. Others were founded in the 1540s along the banks of navigable rivers near San Juan. From the late 17th century on, huge extensions of land were dedicated to commercial agriculture. Those dedicated to raising sugar cane were called haciendas azucareras, the sugar plantations.

In the following centuries, several historical events affected the cultivation and processing of sugar. Except for the decline in sugar production that occurred in the 17th century, the industry experienced various periods of prosperity. The first significant surge occurred between 1790 and 1849. It was largely due to the agrarian reforms of 1776 and the Real Cédula de Gracias of 1815. These measures partially revoked the Spanish monopoly on commerce, as well as making it easier to traffic in African slaves. Also, demand for Puerto Rican sugar by the United States increased as production and export of sugar from Haiti were affected by the chaos of the Haitian revolution. By the middle of the 19th century, there were 789 sugar plantations in Puerto Rico.

Despite this increase, cultivation and processing of sugar went through difficult times at the end of the 19th century. Various factors contributed to this decline, including the depreciation of unrefined sugar and a reduction in production volume caused by plagues, droughts and hurricanes. Obligatory taxes and the technological backwardness of most of the plantations combined to worsen the problems. Events such as the abolition of slavery in 1873 and the tariff wars between Spain and the United States also adversely affected industry conditions.

With the establishment in 1873 of the first sugar factory, the San Vicente mill in Vega Baja, the industry and its diverse forms of production began to be transformed. New technologies were developed in the mills, which produced their own electricity for machinery for processing the sugar. Some of the old plantations transformed their operations and became mills. At the same time, the Puerto Rican colono arose, farmers who grew cane and sold it to the mills for processing.

In 1898, following the Spanish-American War, the industry experienced additional changes. United States investors replaced many of the established European investors on the island. Huge sugar mills such as the Guánica Central and Fajardo Sugar were established. The increase in the price of sugar on the world markets, as well as the investment of capital, made Puerto Rico into one of the principal producers of sugar internationally. Despite this, the sugar industry required a large number of laborers who were submitted to conditions similar to those of slavery.

During the first decades of the 20th century, the sugar industry continued to develop and reached its peak. Despite the establishment of huge sugar trading businesses, some mills backed by Puerto Rican capital also showed considerable production capacity. By 1930, there were 44 mills in operation. In the 1940s, however, the mills began to weaken, due to various factors. The fall in the price of sugar, mismanagement by some administrators, the restriction of credit to independent farmers, as well as the strikes by workers, created conflict and conditions that led to the decline and eventual closure of many of the mills in the subsequent decades.

Following the record sugar cane harvest of 1952, the industry experienced an accelerated deterioration. Additionally, the production of sugar took a lower priority as the government undertook to industrialize the island. Between 1951 and 1968, 17 mills ceased operations. At the end of the 1960s, the government tried to rescue the industry through a recovery program. The Land Authority acquired a significant number of mills and in 1973 created the Sugar Corporation. Despite the fact that the government became the principal sugar producer in Puerto Rico, the mills, both privately and publicly funded, were shut down, one by one. In 2000, operations ceased at the last mills still functioning: Roig in Yabucoa and Coloso, which had operated for nearly 100 years in the municipality of Aguada. Some of the mills also included refineries and packaging operations, whose refined white sugar, with its fine grain, built the reputation of the Puerto Rican sugar producers as true artisans.

The cultivation of sugar cane and the production of sugar were an integral part of the socioeconomic development of Puerto Rico in the 19th and 20th centuries. Sugar cane (Saccharum Officinarum) is a vibrant plant in the grass family with straight and cylindrical stalks with knots at intervals. The plant is originally from India and arrived on the island from Santo Domingo in 1515. In Puerto Rico, as in other tropical regions, the stalk grows for 12 to 18 months and is harvested, generally, between January and May. The process of producing sugar from the cane is a long and complex one that extends from the preparation of the soil and planting through the commercialization of the refined sugar.

The first stage in production is preparing the ground, which consists of plowing, harrowing and smoothing the soil. Pesticides and fertilizers are applied and then the shoots are planted, which must be watered every 15 days. Sugar cane requires a lot of water to grow, so growers use irrigation frequently. The harvest takes place 6 to 12 months after the planting. The cane is cut and gathered by hand, although in the 20th century the producers began to use machinery that gathered the stalks that were cut by hand by the cane cutters. Once cut, the stalks are transported to the sugar mill where the processing begins.

The process of producing sugar consists of various stages. First, the harvest is analyzed, weighed and unloaded. A sample of the cane is analyzed to determine the exact amount of sugar it contains, as well as its quality. Each unit, which also is labeled with information about the owner and where it was grown, is weighed before being unloaded onto what is known as the distribution platform, made of perforated sheets of metal. There, the stalks are washed with water. If they are not washed, the efficiency of the grinding, as well as the general operation of the mill, is adversely affected.

The next stage is known as the pressing station. Here, the cane is cut and pressed to extract the juice, which is called guarapo. This phase is commonly called milling, similar to grain being ground in a mill. The fibrous waste of the leftover cane, which is called bagazo, is used to fuel the boilers that produce electricity for the mill.

In the heating stage, the juice extracted from the cane is weighed to determine the efficiency of the press and to account for the sugar produced in the processing. Lime and other chemical components are added as clarifying agents. Then the juice is heated to a temperature of 225° F to eliminate the impurities in it.

In the clarification stage, the juice is transferred to clarifiers where it is purified and then strained. The sediment that remains in the bottom of the clarifier, known as cachaza, is sent to the filtration station to recover the juice it still contains. The juice is sent to evaporators where it is concentrated to form melao, or the syrup made from the cane. In the next station, the syrup is crystallized. The syrup is transferred to containers called tachos and is reduced further to produce a substance like sugar and honey.

The cooked substance is then cooled in cylindrical containers before going to a high-speed centrifuge, which separates the sugar crystals from the syrup. During this process, the impurities in the syrup are removed, and then it is dried and cooled. The raw sugar is weighed and is then transported to the warehouse.

The raw sugar that is very pure is packed and sent to refineries, where it is processed into commercial white sugar. The raw sugar of lower purity is used as seed stock for the crystallization process in the tachos to help the processing of the syrup. The low-purity syrup is used for manufacturing alcohol and for animal feed and other products.

Adapted by the PROE Editorial Group
Original source: Duhamel Zayas Rivera, “Procesos agrícolas y fabril de la caña de azúcar,” Chapter 10 of El verdor y dulce de nuestra caña de azúcar, 2003.

From the late 19th century to the middle 20th century, the economy of Puerto Rico depended primarily on the cultivation of sugar cane for the production of sugar. During this era, sugar mills called centrales were established and huge tracts of land for cultivating cane were purchased. These factories squeezed the juice from cane with machinery that was originally steam-powered, and later driven by electricity produced by the mill itself. Each of these mills had its own production capacity. The particular characteristics of its housing and industrial structures varied according to the preferences of the owners or the needs of production. However, the mills did have some typical architectural structures.

The sugar mills were more than industrial centers. In almost all cases, they also included small communities with individual residences or barracks for the workers. In the largest mills, there were also stores, hospitals and schools. The owner and his family often lived intermittently in the main house. The management and professional staff, as well as administrators, chemists and engineers, with their respective families, lived permanently at the mill. Their houses were typically a single story, raised above ground, built of wood with roofs of corrugated, galvanized zinc. The porches were broad and were protected from insects by metal screens. These houses were located near the plaza or the industrial buildings and the access roads.

The mill was the principal structure and was typically large, up to four stories tall, with mezzanines and various rooms. They were built over steel or wood frames with a roof of corrugated, galvanized steel. The room for pressing cane, where the drivers delivered the sugar cane, was located in front of the batey, the area where the cane was unloaded by the growers. At the opposite end where the boiler and the storage area for the bagasse, the biomass waste of the crushed cane. This structure was generally wide and tall, generally only one story. A platform crane was used to move the heavy cane to the presses. The area for the boiler and the storage for the bagasse might be part of the room where the press was located or could be located in independent buildings. The boilers were so massive and tall that they filled almost all the space in one wing, except for the wide aisles that separated and surrounded them. The chimneys were attached to this room.

The building where the cane juice, called guarapo, was processed was sometimes even larger than the room for the press, but it was sometimes divided into four levels. The division was a function of the two processes being carried out: clarifying the juice and crystallizing or draining the sugar. Some of the machinery found in this area included the cooking pans, the receiving tanks for the juice, the mixers, the heaters, the clarifiers and the centrifuges. The arrangement of the machinery and the plumbing that carried the juice, syrup, water, and steam varied from one mill to another and from one era to another, as new technologies were disseminated and integrated.

The administrative offices generally were found in a single two-story structure located adjacent to the plaza. It was built of wood or masonry, depending on the era in which that particular mill was constructed. However, some mills broke this pattern and the offices were located in structures or parts of buildings that had originally had another function.

There also were other secondary structures that may or may not have been attached to the main complex, such as the laboratories, the workshops and the general warehouses. In the laboratories, the juice, sugar and cane were analyzed chemically to determine their grades of purity. In general, if the mill operated a train, there were mechanical workshops where spare parts were made for the machinery using drills, presses, and other equipment; or blacksmith workshops, where parts were made using thermal treatments. Finally, the general warehouses were independent structures of modest size that could be located anywhere around the periphery of the industrial area. There might be one or several warehouses and their use frequently changed, which makes it difficult to characterize them.

Adapted by the PROE Editorial Group
Original source: State Office of Historic Conservation, La central azucarera en Puerto Rico (1898-1952), Volumen I: Contexto histórico y tipología de sus elementos, 199?

Interactive Map

Select the location on the map you want to explore.

This post is also available in: Español