Yellow split peas

A seed that fed the first farmers

The pea (Pisum sativum L.) is native to Southwest Asia and was among the first crops people cultivated. Wild peas still grow in Afghanistan, Iran and Ethiopia according to a Wisconsin and Minnesota crop guide, and the wild subspecies P. sativum subsp. elatius ranges across the Mediterranean basin from Spain to the Middle East. A 2018 genetic study places archaeological evidence for cultivated pea around 10,000 BC in the Near East and Central Asia. The same study lists the traits that farmers selected: pods that do not burst open, seeds without dormancy, and a thin, smooth seed coat. All three suit a crop that is harvested in bulk and stored dry.

From the Fertile Crescent the pea travelled with farming. Archaeological and linguistic evidence suggests it moved west through the Danube valley, Greece and Rome into Europe, and east to Persia, India and China. Charred peas have turned up in Swiss lake dwellings and Neolithic farming villages. The Ethiopian pea, Pisum abyssinicum, is a separate case: genetic work indicates a separate domestication from a different wild gene pool, with its earliest known remains, from present-day Eritrea, dating to about 400 AD.

In medieval Europe the pea was above all a dried food. Dried peas could be stored almost indefinitely and were boiled into pease porridge, pottage or pudding, a daily staple on peasant hearths. By the fifteenth century gardeners had developed peas meant to be eaten fresh and green, and these quickly became the choice of upper-class diners, a passion that reached the court of Louis XIV. Robert May's pease pottage of 1660 began, "Take the best old pease you can get", and boiled them with bacon and a bundle of mint. In New France the same dried pea fed soldiers: in the 1750s the French garrison at Fort Chambly in Quebec drew a ration of bread, lard and dried peas, and Parks Canada deduces that their usual meal resembled pea soup.

Yellow split peas are the modern form of that old staple. When the coat was first taken off and the seed halved is not recorded; the result is now a standard commodity.

What a yellow split pea is

A yellow split pea is the dried, mature seed of a yellow-seeded field pea with its seed coat removed and its two halves, the cotyledons, separated. The halves are the food store of the embryo, mostly starch and protein. Smooth green- and yellow-seeded varieties are the ones used for dry split peas for human food, according to the crop guide; green types have been less favoured by buyers because the seed bleaches in the field at harvest if pods sit on wet ground. The word split describes the prepared form, and yellow or green describes the seed-colour class.

Splitting and dehulling are usually one operation. Dehulling removes the seed coat and splits the cotyledons, and a split pea is one of the familiar examples of a dehulled grain legume. The seed is first dried, ideally below 14% moisture and often to about 12%, then abraded or milled, and usually cleaned, sieved and colour-sorted. The hull is about 90% insoluble fibre, so the dehulled product has a higher protein content than the whole seed, although the cotyledons still carry plenty of dietary fibre. Dehulling usually takes a small portion of the cotyledons with the hull, and that dust-sized fraction is a low-value by-product. The market is not perfectly tidy: Canadian grading rules recognise splits in which cotyledons are still loosely held by seed coat.

Yellow split peas are not yellow lentils, chana dal or chickpeas. Health Canada lists split peas, chickpeas and lentils as separate foods, and they come from different plants. Pea flour, pea protein and pea starch are different materials made from the seed, not other names for split peas.

Growing and drying the crop

The field pea likes cool weather. The Wisconsin and Minnesota guide gives an optimum mean temperature of roughly 55 to 65 degrees Fahrenheit and warns that hot weather during flowering makes flowers blast and cuts seed set. It is a spring annual, seeded as early as the soil allows, and in the Upper Midwest it matures in 95 to 100 days. Soils should be well drained, with a pH of about 5.5 to 6.5. The plants are vines, which makes harvest awkward; harvest usually comes with the wheat harvest or as soon as the seed is hard, and a delay or wet pods lying on the ground brings shattering losses and bleached seed. The guide recommends keeping dry field pea at 14% moisture for safe storage.

Yellow peas are a major crop on the Canadian Prairies. Manitoba Agriculture reports that peas grow mainly in the western part of the province, where soils are well drained; in 2022 more than 188,600 acres were planted and 255,558 tonnes of dry peas were harvested. Most are yellow, and they supply both food and animal-feed markets. In 2022 the province exported dried, shelled or split peas worth $58.7 million. These figures describe one modern supply chain, not the origin of split-pea cooking.

Pea seed is rich in protein. Manitoba puts dry peas at 22.7% protein, and Minnesota trials in the 1980s measured 23 to 27%. The Wisconsin guide notes that peas are high in lysine and tryptophan two amino acids that cereal grains are typically short of, so peas can supplement cereal-based diets. Figures from different cultivars and methods are not directly comparable, but they explain why the pea is both a bulk starch and a real protein source.

What happens in the pot

A whole dry pea presents its seed coat to the water first, and the coat slows water uptake. A dehulled seed cooks faster, and a dehulled split pea can collapse into a purée, whereas a whole dehulled seed keeps its shape. In a pot of simmering water the starch granules swell and gelatinize and the cell walls loosen, so the halves soften into a thick, smooth mass. That is why split peas thicken soup without a roux and fall apart into pease pudding.

Cooking also changes how digestible the starch is. In a study of red kidney beans and yellow and green peas, the raw legumes held more than 30% resistant starch on a dry basis. Cooking, soaked or unsoaked, gelatinized the starch and opened its structure to digestive amylase, shrinking the resistant fraction and raising the digestible fractions; pressure cooking did this more strongly. Splitting had a marked effect on starch digestibility in raw and cooked seed, and the authors conclude that the seed coat plays a key role. Soaking reduced the starch fractions, possibly because soluble components leached out.

Soaking is optional. Health Canada states that dry lentils and split peas do not need an overnight soak, and the Alaska extension service reports that split peas are tender about 30 minutes after boiling starts. Cooks who do soak, as in the Fort Chambly soup, which prefers peas soaked overnight and then simmers them for about two hours with salted lard, are choosing texture and time, not meeting a requirement.

Soup, pudding and sweet

The Fort Chambly soup is the clearest picture of the pea as a soldier's food. Parks Canada's reenactment recipe uses 500 g of yellow or green dried split peas with 1.5 litres of water, a large chopped onion, 250 g of diced salted lard, 5 g of salt and 10 g of pepper. The lard is rendered first, the onion cooked in it, the peas stirred in and the water added; the pot simmers covered for a good two hours, and about 30 minutes before serving dried parsley, thyme, chervil, savoury, sage and sorrel go in. Parks Canada is plain that the soup is a deduction from the ration lists rather than a preserved original recipe.

In south Wales the same peas become a solid. Museum Wales records a Gower pease pudding: half a pound of split peas, washed and soaked overnight, are tied loosely in a muslin bag and boiled briskly for about two hours until soft. The peas are pressed through a fine sieve and beaten with an egg, a little butter and sugar, salt and pepper, shaped on a floured cloth, rolled up and boiled for a further half hour. The pudding is turned out hot, sliced and served with salt beef or pork. The museum gives no date for the recipe.

In Beijing the peeled yellow pea becomes a sweet. Wandouhuang, literally pea yellow, began as a Han folk snack, a coarse cake with small red dates sold at temple fairs from wheelbarrows, and was refined in the Qing imperial kitchen into a finer, smoother form. Beijing custom calls for eating it on the third day of the third lunar month. A story holds that the Empress Dowager Cixi heard a vendor's gong near Beihai, summoned him and kept him in the palace to make it; the story is a tale, not dated history. The published recipe takes 230 g peeled dried yellow peas, 2 g baking soda and 65 g sugar. The peas soak 5 to 6 hours with the soda, are rinsed four or five times, boiled until most burst, strained into a smooth paste, simmered with the sugar until thick and chilled for more than four hours before cutting. Soda and sugar belong to that dessert, not to every pea dish.

Home soups appear in extension-service pamphlets as well. The University of Alaska Fairbanks gives a split-pea soup with onion, carrot, celery, broth and optional ham, and uses split peas in a many-bean soup, where the split peas join the pot late. Between them, the soup, the pudding and the sweet show the same cotyledons as a thickener, a sliceable solid and a smooth paste.

The pea in a koji garum

Peaso garum is a vegetarian garum made with cooked yellow split peas as its protein. For one jar of about 1 kg of mash, 400 g of cooked peas are blended with 250 g of rice koji, 250 g of water and 100 g of salt, which is 10% of the mash; a larger crock doubles every amount. The slurry is sealed with a loose lid or in a vacuum bag and held at 55 to 60 degrees Celsius for 2 to 6 weeks, stirred or massaged every couple of days. Liquefaction starts in the first week, and the finished liquid is strained through cloth, yielding 700 to 800 ml from a jar.

The pea supplies the substrate and the koji supplies the enzymes. Proteolysis by microbial proteases produces the free amino acids and short peptides behind the savoury taste of the family of seasonings that runs from African legume ferments to Asian soy pastes, and in this mash the pea's protein, roughly a quarter of the dry seed, is what the enzymes work on.

The mash is low in acid. Its finished pH is about 5.0 to 5.8, above the 4.6 line, so it is not an acid ferment: salt and the warm hold are the only barriers. Peaso garum is a perishable fridge or freezer seasoning and is not shelf stable. Salt should not fall below about 8%, the garum must not be canned, and the warm enzymatic process is not validated as a botulism control. A batch that smells of ammonia or rot, bloats a sealed bag or grows pink or black surface growth is discarded.

Notes and open questions

The date when yellow split peas were first dehulled and halved is not recorded. The Wisconsin crop guide dates from 1991, so its yields and protein values describe older cultivars. For peaso garum the pea cultivar, the cooking time, the dry-to-cooked weight and the target mash texture are not fixed, and the dehulling description comes from a source on pulses in general, with faba bean as its worked example.