I am obviously biased, but I think bread is amazing. It tastes great and inhabits the now as fully as a zen buddhist priest; it’s a constant science experiment and getting bread right requires the most attuned and practical, if somewhat instinctual, manipulation of local biochemistry. Bread also has a history as long as civilisation. (In fact, the history of bread grains really is the history of human civilisation.) Bread should just be a compulsory subject in schools! Bread is science and maths and history and mindfulness, not to mention religious and cultural studies all in one… But you eat it; so cool!

In The Rye Baker, Stanley Ginsberg explains how technological innovation and climate change have determined the role of this grain over millennia. This book has masses of information (and a ton of recipes), but the history it tells about rye will have you wanting to eat rye bread today…

In short(ish):

…some 13,000 years ago… Rye was really just an accidental food
Archaeological evidence suggests that rye first “entered the human diet as a stowaway, a humble weed hidden among the harvest.” (p.14)

…some 12,000 years ago… Climate Change made rye a more prominent and preferable grain
“Then something very interesting happened - something that foretold the weed’s future. About 12,000 years ago, Earth entered a period of global cooling that academics call the Younger Dryas, aka “The Big Freeze.” Along with the rest of our planet, the Fertile Crescent turned dry and cold. Barley and einkorn struggled in those conditions, but rye flourished. And so the farmers followed the path of least resistance - and greatest yield. For 1,300 years, the abundance of domesticated rye in ancient grain troves attests not only to its importance in the human diet but also to its newly recognised standing as one of the founder crops in the Near East.
But, The Big Freeze waned, Earth warmed, and barley and einkorn regained their dietary preeminence. For the next five millennia, rye surfaced only sporadically in the Fertile Crescent… [then] disappears from the Near Eastern archaeological record.” (p.14)

…some 6,000+ years ago… Rye made its way to Europe where the conditions were perfect for its growth
Rye may have disappeared from the Near Eastern archaeological record at that time, but “It found a new home in central Europe. More than 6,000 years ago, rye appeared as a wild grain in modern Greece, the former Yugoslavia, and Ukraine. Cultivated rye first appears in what is now Poland and Bulgaria, brought there by farmers who migrated from the Middle Danube region. It flourished in the region’s clay and acidic, sandy soils, as well as its dry, cold climate.
”Unlike wheat, millet, and barley, rye withstood drought conditions, germinated at temperatures near freezing, and resisted winterkill even at forty below zero. And so throughout its new environment, rye prevailed over wheat, oats, and barley.” (pp.14-15)

…during the pre-Roman Iron Age through Roman times… technology gave rye greater prominence
“Rye cultivation continued to spread across Europe during the pre-Roman Iron Age and was a staple grain during Roman times …but hardly loved. Rye benefited from two important technological advances that drove the rapid expansion of European agriculture between 500BC and AD1000 - widespread adoption of the iron sickle and the appearance of the heavy plow.
“Until the Iron Age, farmers had harvested their grain crops ear by ear, choosing only the more desirable cereals, typically wheat and barley, leaving weeds like rye for the birds and rodents. The practice made for inefficient but highly selective harvesting, conferring an artificial advantage to grains preferred for their look and taste."
“With the iron sickle, farmers could clear-cut their fields close to the ground, which was more efficient but far less selective, collecting in the process weeds like rye along with the more desirable grains. Over time, as farmers replanted part of their harvest, the proportion of rye naturally increased in places where marginal conditions favored its growth.
“The heavy plow further cemented rye’s presence in the grain fields. Unlike its predecessor, the scratch plow… the heavy iron plow dug deep into the dense clay soils of northern Europe, improving drainage and bringing nutrient-rich subsoil layers to the surface. The new plow also changed patterns of land use… [letting some farmers] sow rye in the same fields year after year [or clear new land for rye cultivation].” (p.15)

…during the High Middle Ages… rye played an important role in massive population growth and migration
“The rapid growth of rye cultivation during the High Middle Ages increased food supply and encouraged migration into formerly inhospitable regions of northern and central Europe. This, in turn, fueled the rise of social infrastructure that created the conditions for massive population growth. In the mid-seventh century, it’s estimated that Europe’s population was stable at around 18 million. By AD1000, it had more than doubled to 38.5 million and then doubled again to an estimated 73.5 million in 1340, a decade before the Black Death of 1348-50 claimed the lives of half that number. Tellingly, most of this growth occurred in the rye-growing regions.
“Throughout the premodern period, bread was the foundation of the European diet at every level of society. [With gruel, bread provided] about 3/4 of their caloric intake. And while wheat may have occupied the top of the grain hierarchy,… rye fed the masses.” (pp.15-16)

…during the establishment of ‘the New World’ and the growth in economic prominence of the USA… rye fueled much of this growth, but technology once again influenced the popularity of rye, allowing wheat to dominate dietary preferences
“Rye came to the New World in the early 1620s…. it was rye and native maize that nourished America during its first 200 years of settlement and westward expansion. But rye’s primacy was not to last. The opening of the western plains and the introduction of mechanized agriculture in the mid-19th century - spurred on by the world’s first mechanical reaper - inundated North America with an ocean of wheat that all but swept rye out of the American diet. [The railroads followed, establishing America’s global economic primacy and the importance of wheat as an important grain for export and sale in America.] (pp.16-17)

…the 20th into the 21st Century… technology changes things again, but so does cultural revolution, so watch this space!
“By the turn of the twentieth century, wheat had conquered America [and become a massively important export commodity]. [Technological developments helped, while] selective breeding programs spawned hardier and more prolific strains of wheat able to thrive in soils and conditions that once supported only rye. The Green Revolution of the 1950s and 1960s, with its emphasis on high-yielding varieties of wheat, corn and rice, expanded wheat’s share of global farm output even further, driving rye back into the margins of food cultures it once dominated.” (p.17)

However, “For the populations of Europe’s northern tier, rye has remained an enduring fixture of their tastes and traditions” (p.17) and many of these breads (so full of national pride and a sense of home for expats) are again gaining popularity as niche breads among the bread lovers of the world.

(Ref: pp.14-17 Stanley Ginsberg (c2016) The Rye Baker; Classic Breads from Europe and America. WW Norton & Company: New York and London)