It should go without saying-- but generally doesn't-- that the modern diet is more or less completely divorced from seasonal imperatives, except in the cases of foodies and gourmets, who firmly decry strawberries in September, lamb in January, and sweet corn and tomatoes outside the crucial July-through-September period. In fact, even skilled cooks often are unaware of what is ripe in what season nowadays. (Part of this is a global culture, where foodies peruse writings from France , Australia , Seattle , California , Florida and Vermont in a single sitting.) More confusing still, what is in season in one's own area of the United States at any given time may be completely unrelated to what was in season at the same date in the medieval period.
Most of the simpler depictions of the medieval life suggest that fresh vegetables and fruits would be completely unobtainable in the winter months. For those familiar with the venerable concept of root-cellars, this idea is ludicrous. We all know that onions and garlic (incidentally considered by medieval writers to be staples of the peasant diet) keep in a dark, dry place for months. Parsnips, in fact, need to be harvested as late as possible. But they are not the only root vegetables considered long-keepers. Turnips, parsnips, carrots, the now-elusive skirret, beetroot, parsley roots-- all can be kept. Modern head cabbage, too, keeps for a very long time-- but as we know, headed cabbage is a relatively late development.
Modern gardeners now extoll the benefits of succession planting-- but a look at gardener's manuals such as Hyll's Gardener's Labyrinth confirms the planting of winter crops of vegetables as well as the inevitable winter wheat and grains. Beet greens (now available as swiss chard), coleworts, spinaches, and other, more exotic greens can be planted in summer for fall harvest or in fall for early spring appearances. Furthermore, depending on the climate and the weather, hardy greens grown in protected areas can keep producing long into the winter.
While year-round availability is a modern invention, various expedients for stretching the growing season were known to medieval gardeners. Le Menagier de Paris gives instructions for potting up violets for a primitive kind of forcing in his homely text. Late 16th century Hyll dictates early starting of cucumber plants in pots, and the use of cuttings from the previous year's plants to get a head-start on the season.
The selection of cultivars, too, could stretch the season-- as astute apple-eaters know, the season for apples even in the US starts in late August and proceeds through various cultivars up into October and early November. This, in a time and place where the variety of cultivars available to us is small and growing smaller. (Apples, due to their unique genetic get up, don't breed true in the seed; so every cultivar must be spread and preserved by the survival of grafts. In fact, most of the cultivars known to our medieval ancestors are unavailable now, though probability suggests that a genetic replica of a medieval type might be produced by any given apple seed. The pear season is equally long, and other, lesser-known fruits such as the medlar (to be harvested after the first frost) increase that time. Pears, apples, quinces and medlars, if harvested carefully and stored in cool dry conditions, will last for months, though gradually their appearance will become unattractive. (My personal theory holds that the variations in the use of raw and cooked fruits of this kind would have depended on the season-- when the fruit was available in peak condition, it would be served raw, but as the winter wore on, the less-attractive stored fruit was cooked, pureed and otherwise altered. The stone fruits, such as sloes (wild plums), cherries, peaches, and apricots, had fewer cultivars, and do not have the same keeping qualities. Berries, also, would have had their specific seasons-- but different berries ripen at different times, stretching that time frame.
The modern person gets much less of their nutrition from pulses/legumes and grains than in the past, but the long-keeping qualities of these foods in their dry state made them perennial staples in the pre-modern era. Which legumes were available and popular was a regional difference-- the mediterranean countries used chickpeas and lentils more than their northern neighbors. Lentils appear with some regularity in many cultures, but the French and English appear to prefer pease. The question of whether these pease were the dried green kind we see, split, in our stores, the rarer yellow pea, or what is now called field peas (most often identified as 'cowpeas') may well be meaningless, since a variety were probably grown. Fava or fava-like beans were the beans of the medieval era, most modern 'dry' beans and string/wax beans having a New World origin. While the young shoots, green pods, and green peas/beans appear as delicacies in cooking, the majority of the crops were allowed to grow to maturity in the fall and harvested for winter use. (Dried peas are of particular interest to the aspiring medieval cook, as pease broth often forms the vegetarian/fast day equivalent to our vegetarian broth.
Nuts, of course, are another prime source of protein that travels well and keeps, if not indefinitely, for a good long time, especially if stored in their shells.. The stylish almond, favorite of fast-day and Lenten cooks, and used even in meat recipes for its peculiar qualities, was a fashionable necessity in the well-off home. More homely walnuts, beech-nuts, etc. make occasional appearances in the cooking and medical literature. Some nuts were pressed to provide a cooking oil, as were seeds such as poppy, hemp and occasionally flax.
These are rough estimates based on English sources, and current modern parameters.
'The good huswifes handmaide for the kitchen' (1594?), published by Stuart Peachey in 1992. :
 To knowe the due seasons for the use of al maner of meats throughout the yeare.
Brawn is best from the holy Rood day til Lent, and at no other time commonlie used for service. Bacon, Beefe and Mutton, is good at all tymes, but the woorst tyme for Mutton is from Easter to Midsommer. A fatte yoong Pig is never out of season. A Goose is worst at Midsommer, best in stubble tyme, but they be best of all when they be young green Geese. Veale is all tymes good, but best in Januarie and Februarie. Kidde and young Lambe is best between Christmasse + Lent, + good from Easter to Whitsontide, but Kid is ever good. Hennes be all times good, but best from Alhallowntyde to Lent. fatte Capons be ever good. Peacocks bee ever in season, but when they be yoong and of a good stature, they be as good as Feasants, + so be yoong Grouces. Sinets be best betweene Alhallowen day and Lent. A Mallard is good after a frost, til Candlemas, so is a Teal and other wild foule that swimmeth. A Woodcocke is best from October to Lent, and so be all other birdes, as Ousels, Thrushes and Robins, and such other. Herons, Curlewes, Crane, Bittour, Bustard, be at all times good, but best in Winter. Feasant, Partridge and Raile, be ever good, but best when they bee taken with a Hawke, Quaile + Larks be ever good Connies be ever in season, but best from October to Lent A gelded Deare, whether he be fallow or red, is ever good. A Pollard is speciallie good in May, at Midsommer he is a Bucke, and verie good till Holy Rood day before Michaelmas, so like wise is a stagge, but he is principal in Maie. A barren Doe is best in Winter. A Pricket and a Sorell syster is ever in season. Chickens bee ever good:and so be yoong Pigeons.
"A proper Newe Booke of Cokerye", c.~1545 C.E. :
"Brawne is beste from a fortenyghte before Mychalmas tyll lente. Beife and BAcon is good at all times in the yere. Mutton is good at all tymes, but from Easter to myd Sommer is worste. A fatte pygge is ever in season. A goose is worste in midsomer mone and beste in stubble tyme, but when they be yong grene geese, then they be beste. Veale is beste in Januarye, and February, and all other times good. Lamb and yonge kydde is beste between Christmas and lente, and good from Easter to Witsontyde. Kyd is ever good. Hennes be good at all tymes but best from November to lente. Fat Capons be ever in season. Pecockes be euer good but when they be yong and of a good stature, they be as good as fesantes, and so be yonge grouces. Sinettes be beste between Al-Hallowen daye and Lente. A mallarde is good after a froste, tyll Candelmas, so is a Teile and other wilde foule that swymmeth. A Wodcocke is best from Octobre to Lente; and so be all other byrds as Ousels and Thrysselles, Robins and such other. Herons, Curlus, Crane, Bitture, Bustarde, be at all times good; but best in wynter. Fesauntes, Partriche and Rayle be euer good but beste when they be taken with a hauke. Quayle and Larkes be euer in season. Connies be ever good and so is a doo. A hare is euer good, but beste from October to Lente. A gelded deer whether he be falowe or readde, is euer in season. A Pollarde is speciall good in maye, at Midsommer he is a Bucke, and is verye good tyll holye Rood day before Mighelmas so lykewyse is a stagge, but he is principal in Maye. A barren doo is best in wynter. A Pricked and a sorrell syster is euer in season. Chekins be euer good, and so bee Pigions yf they be younge."
Gervase Markham, The English Housewife 1615
Touching the powdering up or potting up of butter, you shall by no means as in fresh butter wash the buttermilk out with water, but only work it clear out with your hands: for water will make the butter rusty, or reese; this done, you shall weigh your butter, and know how many pounds there is thereof, for should you weigh it after it were salted, y ou would be deceived in the weight: which done, you shall open the butter, and salt it very well and thoroughly, beating it in with your hand till it be generally dispersed through the whole butter; then take clean earthen pots, exceedingly well leaded lest the brine should leak through the same, and cast salt into the bottom of it: then lay in your butter, and press it down hard within the same, and when your pot is filled, then cover the top thereof with salt so as no butter be seen: then closing up the pot let it stand where it may be cold and safe... (p. 173-174)
Gervase Markham, The English Housewife 1615:
Your preserved sallats are of two kinds, either pickled, as are cucumbers, samphire, purslane, broom, and suck like, or preserved with vinegar, as violets, primrose, cowslips, gillyflowers of all kinds, broom flowers, and for the most part any wholesome flower whatsoever.
Now for the pickling of sallats, they are only boiled, and then drained from the water, spread upon a table, and a good store of salt thrown over them, then when they are thorough cold, make a pickle with water, salt, and a little vinegar, and with the same pot them up in close earthen pots, and serve them forth as occasion shall serve.
Now for preserving sallats, you shall take any of the flowers before said after they have been picked clean from their stalks, and the white ends (of them which have any) clean cut away, and washed and dried, and, taking a glass pot like a gallipot, or for want thereof a gallipot itself; and first strew a little sugar in the bottom, then lay a layer of the flowers, then cover that layer with sugar, then lay another layer of the flowers, and another of sugar; and thus do one above another till the pot be filled, ever and anon pressing them hard down with your hand: this done, you shall take of the best and sharpest vinegar you can get (and if the vinegar be distilled vinegar, the flowers will keep their colours the better) and with it fill up your pot till the vinegar swim aloft, and no more can be received; then stop up the pot close, and set them in a dry temperate place, and use them at pleasure, for they will last all the year.
"Take rote of persel, of pasternak, of rafens, scape hem and waische
hem clene. Take rapes & caboches, ypared and icorue. Take an erthen
panne with clene water & set it on the fire; cast alle thise therinne.
Whan they buth boiled cast therto peeres, & parboile hem wel. Take alle
thise thynges vp & lat it kele on a faire cloth. Do therto salt; whan it
is colde, do hit in a vessel; take vyneger & powdour & safroun & do therto, & lat alle thise thynges lye therin al nyyt, other al day. Take wyne greke & hony, clarified togider; take lumbarde mustard & raisons coraunce, al hoole, & grynde powdour of canel, powdour douce & aneys hole, & fenell seed. Take alle thise thynges & cast togyder in a pot of
erthe, & take therof whan thou wilt & serue forth."
- -Curye on Inglish, p. 120-121
From the Danish/Icelandic Manuscript:
How to make a sauce for lords and how many days it keeps. Take cloves, and nutmeg, cardamom, pepper, cinnamon, that is canel, and ginger, an equal weight of each, but the cinnamon should be as much as all the other spices, and also fried bread twice as much as all the rest. Crush it all together, and grind with strong vinegar and put into a cask. This is lord's sauce and is good for six months.
How to make use of the above sauce. When you want to use some of it, then boil it well in a pan on hot embers without flame. And take a steak of hart or deer, well larded, and cut into thick slices. And when the sauce is cold, then place the game in it with a little salt and it can be kept there for three weeks. In this way one can preserve steaks of hart, geese and ducks, if cut thick. This is the best sauce that the lords have.
"TO PRESERVE COWCUMBERS ALL THE YEERE. (DELIGHTES FOR LADIES, Sir Hugh
You may take a gallon of faire water, and a pottle of veriuyce, and a pinte of
bay salt, and a handfull of greene Fennell or Dill: boile it a little, and
when it is cold put it into a barrell, and then put your Cowcumbers into that
pickle, and you shall keepe them all the yeere."
Mikolaj Reg in "Zywot czlowieka pozciwego" (1568) describes a sauerkraut method: "Having romoved the outside leaves of some nice heads of cabbage, cut them in half and fit them neatly into a vat, spreading beet chards & dill between the layers"
To Make Pickled Cabbage
Ein Kochbuch aus dem Archiv des Deutschen Ordens, 15th Century.
31. If you want to make pickled cabbage Boil white cabbage heads, take two parts mustard and one part honey, mix them with wine and add caraway /einß/ (?) it enough, put the boiled cabbage into it and serve it cold. You can also season the broth and serve it.
Ein Buch von Guter Spise, 14th c.
Translated by Alia Atlas
Flavor caraway seeds and anise with pepper and with vinegar and with honey. And make it gold with saffron. And add thereto mustard. In this condiment you may make sulze (pickled or marinated) parsley, and small preserved fruit and
vegetables or beets, which(ever) you want.
Marx Rumpolt, Ein New Kochbuch, 1581
3. Rote Ruben: Red beets preserved with small cut horseradish/ anise/ coriander/ and a little caraway/ special if the beets are cut/ marinated in half wine and half vinegar.
To Pickle Mushrooms
Lady Elinor Fettiplace's Receipt Book, 16th century
Take your Buttons, clean ym with a sponge & put ym in cold water as
you clean ym, then put ym dry in a stewpan & shake a handful of salt
over ym, yn stew ym in their own liquor till they are a little
tender; then strain ym from ye liquor & put ym upon a cloath to dry
till they are quite cold. Make your Pickle before you do your
mushrooms, yt may be quite cold before you put ym in. The Pickle must
be made with White-Wine, White-Pepper, quarter's Nutmeg, a Blade of
Mace & a Race of ginger.
Sir Kenelm Digbie's The Closet Open'd, 17th century
Cut the great ones into halves or quarters, seeing carefully there be no worms in them; and peel off their upper skin on the tips: the little ones, peel whole. As you peel them, throw them into a basin of fair-water, which preserves them white.
Then put them into a pipkin or possnet of Copper (no Iron) and put a very little water to them, and a large proportion of Salt. If you have a pottle of Mushrooms, you may put to them ten or twelve spoonfuls of water, and two or three of Salt. Boil them with a pretty quick-fire, and scum them well all the while, taking away a great deal of foulness, that will rise. They will shrink into a very little room. When they are sufficiently parboiled to be tender, and well cleansed of their scum, (which will be in about a quarter of an hour,) take them out, and put them into a Colander, that all the moisture may drain from them.
In the mean time make your pickle thus: Take a quart of pure sharp
white Wine Vinegar (elder-Vinegar is best) put two or threee
spoonfuls of whole Pepper to it, twenty or thirty Cloves, one Nutmeg
quartered, two or three flakes of Mace, three Bay-leaves; (some like
Lemon-Thyme and Rosemary; but then it must be a very little of each)
boil all these together, till the Vinegar be well impregnated with
the Ingredients, which will be in about half an hour. Then take it
from the fire, and let it cool.
When the pickle is quite cold, and the Mushrooms also quite cold, and
drained from all moisture: put them into the Liquor (with all the
Ingredients in it) which you must be sure, be enough to cover them.
In ten or twelve days, they will have taken into them the full taste
of the pickle, and will keep very good half a year. If you have much
supernatant Liquor, you may parboil more Mushrooms the next day, and
put them to the first. If you have not gathered at once enough for a
dressing, you may keep them all night in water to preserve them white, and gather more the next day, to joyn to them.
A Proper New Booke of Cokerye (of the sixteenth Century),
edited by Catherine Frances Frere, Cambridge 1913.
For to Make Wardens in Conserve
Fyrste make the syrope in this wyse, take a quarte of good romney and putte a pynte of claryfyed honey, and a pounde or a halfe of suger, and myngle all those together over the fyre, till tyme they weeth, and then set it to cole. And thys is a good sirope for manye thinges, and wyll be kepte a yere or two. Then take thy warden and scrape cleane awaye the barke, but pare them not, and seeth them in good redde wyne so that they be wel soked and tender, that the wyne be nere hade soked into them, then take and strayne them throughe a cloth or through a strayner into a vessell, then put to them of this syroope aforesayde tyll it be almost fylled, and then cast in the pouders, as fyne canel, synamon, pouder of gynger and such other, and put it in a boxes and kepe it yf thou wylt and make thy syrope as thou wylt wourke in quantyte, as if thou wylt worke twenty wardens or more or lesse as by experience.
Le Menagerie De Paris 1393
To make Candied Orange Peel, cut the peel of an orange into five pieces and scrape away the loose skin inside with a knife, then se them to soak in good fresh water for nine days and change the water daily then boil them letting them come once to the boil only, in fresh water and this done spread them on a cloth and let them dry thoroughly then put them in a pot of honey until they be quite covered therewith and boil on a slow fire and skim. And when you think that the honey is cooked ( to try if it be cooked, have some water in a spoon and pour a drop on the honey into the water and if it spreads it is not done and if the drop of honey remains in the water without spreading then it is done), then you must take out your pieces of orange peel and set out a layer in order and sprinkle poudered ginger thereon then another layer and sprinkle etc, usque in infinitam, and leave them for a month or more and then eat them.
Gervase Markham, 1615:
To make conserve of any fruit you please, you shall take the fruit you intent to make conserve of; and if it be stone fruit you shall take out the stones; if other fruit, take away the paring and core, and then boil them in fair running water to a reasonable height; then drain them from thence, and put them into a fresh vessel with claret wine, or white wine, according to the color of the fruit; and so boil them to a thick pap all to mashing, breaking, and stirring them together; then to every pound of pap put to a pound of sugar, and so stir them all well together, and, being very hot, strain them through fair strainers, and so pot it up. (p 116)
Platina, On Right Pleasure and Good Health,
You will be able to keep plums and all kinds of apples, as well as cherries, pears and other fruits, for a long time when they are picked with their stems and put in honey, so long as they do not touch each other. (p. 18)
To keep mulberries fresh for a long time, you do this: press the juice out the mulberries and mix it with new wine and place it in a glass jar with the mulberries. You will keep them fresh for a long time. (p. 19)
Pears are preserved in as many ways as grapes, apples, plums, peaches and quince. Similarly all apples are preserved very well if the fruit cellars are placed in rows and have windows facing from south to north. They ought to be strewn with straw and chaff so they will not rot from too much dampness, which arises from contact. (p. 26-27)
It is agreed by all authors that figs and well-matured grapes are less unhealthy than other fruits that are eaten raw, and eaten as a first course, they cause almost no harm. If grapes are ripe and have been picked for a long time or have been hung up for at least four days, they are milder and sweeter when eaten, for they fatten, refresh, and do not cause squeamishness; eaten fresh, however, they upset the stomach, the breathing, and the bowels with bloating, they harm the head and they cause drowsiness. While eating grapes, one should not grind the grapeseeds with one's teeth... Grapes stored in sweet wine, as is accustomed to be done, affect the head. They are also considered preserved by suspension if they are preserved in straw. Some preserve them in a heap of grapestones. . .
You can also preserve green grapes this way. Take unblemished grapes from the vine and cook down in river water to one-third. Put this together with fresh grapes into a well-sealed jar so that air cannot enter. Put the grapes in a cool place where the sun has no access, and you will find them green whenever you wish. . .
Condensed grape is made from grapes boiled down in the pot, while condensed must is made from pure must which has been condensed in special defrutum jars... (p. 27-28)
To keep pomegranates for a long time, plunge them in boiling water, remove them at once, and hang them up. (p. 29)