There are a lot of varieties of rice out there, but the key divide we want to make early is between dry-rice and wet-rice. When we’re talking about “rice cultures” or “rice agriculture”, generally, we mean wet-rice farming, where the rice is partially submerged during its growing. Wild rice, as far as we can tell, began as a swamp-grass and thus likes to have quite a lot of water around, although precisely controlling the water availability can lead the rice to be a lot more productive than it would be in its natural habitat. While there are varieties of rice which can be (and are) farmed “dry” (that is, in unflooded fields much like wheat and barley are farmed), the vast majority of rice farming is “wet”. As with grains, this is not merely a matter of different methods of farming, but of different varieties of rice that have been adapted to that farming; varieties of dry-rice and wet-rice have been selectively bred over millennia to perform best in those environments.

Wet-rice is farmed in paddies, small fields (often very small – some Chinese agronomists write that the ideal size for an individual rice field is around 0.1 hectare, which is just 0.24 acres) surrounded by low “bunds” (small earthwork walls or dykes) to keep in the water, typically around two feet high. Because controlling the water level is crucial, rice paddies must be very precisely flat, leading to even relatively gentle slopes often being terraced to create a series of flat fields. Each of these rice paddies (and there will be many because they are so small) are then connected by irrigation canals which channel and control the water in what is often a quite complex system.

The exact timing of rice production is more complex than wheat because a single paddy often sees two crops in a year and the exact planting times vary between areas; one common cycle on the Yangtze is for a February planting (with a June harvest) followed by a June planting (with a November harvest). In other areas, paddies planted with rice during the first planting might be drained and sown with a different plant entirely (sometimes including wheat) in the intervening time.

The cycle runs thusly: after the heavy rains of the monsoons (if available), the field is tilled (or plowed, but as we’ll see, manual tillage is often more common). The seed is then sown (or transplanted) and the field is, using the irrigation system, lightly flooded, so that the young seedlings grow in standing water. Sometimes the seed is initially planted in a dedicated seed-bed and then transferred to the field, rather than being sown there directly; doing so has a positive impact on yields, but is substantially more labor intensive. The water level is raised as the plant grows; agian this is labor intensive, but increases yields. Just before the harvest the fields are drained out and allowed to dry out, before the crop is harvested and then goes into processing.

Rice is threshed much like grain (more often manually threshed and generally not threshed with flails) to release the seeds, the individual rice grains, from the plant. That is going to free the endosperm of the speed, along with a hull around it and a layer of bran between the two. Hulling was traditionally done by hand-pounding, which frees the seed from the hull, leaving just the endosperm and some of the bran; this is how you get brown rice, which is essentially “whole-grain” rice. While it is generally less tasty, the bran actually has quite a lot of nutrients not present in the calorie-rich endosperm. Whereas white rice is produced by then milling or polishing away the bran to produce a pure, white kernal of the endosperm; it is very tasty, but lacks many of the vitamins that brown rice has.

Consequently, while a diet of mostly brown rice can be healthy, a diet overwhelmingly of white rice leads to Thiamine deficiency, known colloquially as beriberi. My impression from the literature is that this wasn’t as much an issue prior to the introduction of mechanical milling processes for rice. Mechanical milling made producing white rice in quantity cheap and so it came to dominate the diet to the exclusion of brown rice, producing negative health effects for the poor who could not afford to supplement their rice-and-millet diet with other foods, or for soldiers whose ration was in rice. But prior to that mechanical milling, brown rice was all that was available for the poor, which in turn meant less Thiamine deficiency among the lower classes of society.

Bret Devereaux, “Collections: Bread, How Did They Make It? Addendum: Rice!”, A Collection of Unmitigated Pedantry, 2020-09-04.