I knew that in feudalism nobles took a large chunk of the food made by farmers in exchange for protection and yada yada

Don't say the F word. People have killed for less around these parts.

Rent during the Medieval period was actually fairly rarely levied in terms of a proportion of a tenant's produce. Food rents did exist, although often with the stipulation that they could in fact be paid in kind or currency, but these were often discrete amounts as part of a wider rent. A major exception to this, the codification of which has unfortunately had a wider impact on conceptions of (specifically Early) Medieval rents are the Early Medieval English 'farms of one night'; royal vils whose whole purpose was to provide pseudo-annual food rents specifically to support the itinerant nature of the Early Medieval English royal court (and on which Ryan Lavelle has an excellent monograph).

To wit; rent was instead most commonly levied in terms of service rather than goods.This typically applied at all levels of society, from the Early Medieval thegn down to the lowliest Gebur. The c11th Century English document known as the Rectitudines singularum personarum is a manual of sorts for estate manageme, thought to have been produced in the city of Bath. The Rectitudines suggest various levels of obligation and mutual recompense throughout the various levels of society.

The thegns - the nobles who hold large estates or hold land directly from the king - are always liable for the trimoda necessitas:

ĐEGEN LAGV IS þæt he sy his boc rihtes wyr|ðe . 7 þæt he ðreo ðinc of his lande do fyrd|færeld . 7 burhbote 7 brycgeweorc

Specifically, a thegn should raise forces for the fyrd, maintain fortifications, and help repair bridges. Other responsibilities, of course, may occur: to help maintain the boundaries of royal estates, to help furnish the navy or stand coast guards or signal watchmen, and to give alms.

Various levels of obligation stand in the peasantry, from the Geneat ('tenant' villager likely holding around 30 acres), to the Kotesetlan (cottager or smallholder likely holding 5-15 acres), to the more vague Gebur, which is closest to what pop-culture might envision as a 'serf'. As the most prosperous class of peasantry, a geneat might be expected to pay some rent in coinage or kind:

Geneat riht is mistlic be ðam ðe onlan|de stænt . on sumon he sceal land gafol syllan 7 gærsswyn

A geneat should pay his land-tax (which suggests he might own his land outright) and might be liable to provide a pig a year to his thegn, but his obligations are largely in forms of service: he might be liable to:

and provide horses for team work and carry loads, labour... reap and mow, cut the animal-hedge, and maintain snares, build and fence the dwellings within an enclosure, and lead newcomers to the enclosure, pay church tribute and alms money, hold head-guard dutiesand guard horses, go on errands, either further or nearer or to wherever he is sent.

A kostetlan's dues are entirely service obligations rather than goods, whether proportional or discrete, although as a freeman he does pay a "hearth-penny" (heorðpænig) annually in tax. A kostetlan is liable for service on his lord's lands (usually fields adjacent to or acre strips within the communal farmlands); the Rectitudines suggest a day a week on his lord's lands, and up to three days a week during the busy harvest season. A kostetlan would also potentially be liable to provide fyrd service for the gesith of his thegn, perhaps under the command of a geneat, or to help man a coast guard or watchtower post, or to provide labour for his thegn's obligations of burhbote and brycgeweorc

The Gebur are the "semi-free", higher in stature and with far more rights than the ðeow - literal slaves - but also with far more service obligations than more free peasantry. The Rectitudines suggest that a Gebur be liable for two days service a week on his lord's land, plus additional duties when required, rising to three during harvest. The Gebur may actually have been liable for some food rents: the Rectitudines suggest he pay "twenty-three sesters of barley, and two hens; at Easter [he must give] a young sheep or two pennies." On top of this he would also be liable annually for ten pence of gafol (tax).