What does the Iberico pig eat, and why does it change the taste of the ham?
Contents
What do Iberico pigs eat? Not all the same thing, and that explains the price gap between two hams that look alike. A pig destined for an acorn-fed ham switches diet in autumn. It goes out into the dehesa and lives on the acorns that have fallen, which is how acorn-fed pigs in Spain finish their fattening. A cebo pig raised indoors never sees an acorn. Between the two sits the cebo de campo pig, outdoors all year and fed mainly on cereals and pulses.
The short answer
For a ham to carry the “de bellota” designation, the pig has to gain at least 46 kg in the dehesa, over more than 60 days, with no supplementary feed. That is a legal requirement, not a selling point.
- The dates are fixed. Animals enter the dehesa between 1 October and 15 December and are slaughtered between 15 December and 31 March.
- Each batch goes in at an average of 92 to 115 kg. A full weight gain over the season takes around 600 kg of acorns per animal.
- Outside the montanera, the same pigs eat cereals and pulses. The cebo de campo pig eats them all year round.
- Acorns leave a trace you can measure. The fat of an acorn-fed pig contains at least 54% oleic acid, and that is why it melts so quickly on a warm plate.
Where these figures come from
The periods, weights and densities quoted here come from Royal Decree 4/2014, the Spanish standard that governs the whole Iberico sector. On 23 August 2026 we reread its consolidated text in the Boletín Oficial del Estado, articles 3, 6, 7, 8, 9 and 12 and the annex. The figures on acorn intake, weight gain and the make-up of the fat come from an article in Ganadería, a farming journal whose archive is kept by the Spanish Ministry of Agriculture.
The rest is what we have seen with our own eyes. We pick our pieces in drying cellars in the Salamanca dehesa, and we spent a whole montanera season filming for our documentary Viva España.
One point of honesty. We sell the products we write about, acorn-fed and cebo de campo alike, and you should know that as you read. It is also why we name no brands and rank no one. Where we could not find a source for a figure, we took it out instead of rounding it.
Bellota vs cebo, two seasons and three ways of raising a pig
The year of an acorn-fed pig falls into two halves, and only the second one is about acorns. Through spring and summer the dehesa has little to give. The grass is dry, the oaks have no fruit yet, and the animals go out mostly in the cooler hours. They are fed on cereals and pulses during that time. On the farm we work with, the mix is blended on site from wheat, barley, almonds and sunflower seed. The raw materials are bought in, and the recipe is ours.
The first acorns drop in late September and the animals change their habits almost at once. They walk for much of the day and pick out the ripest fruit. We watched it while filming, and they really do choose. This season, the montanera, decides the make-up of the fat and the legal grade of the piece.
Only animals that go through a montanera give a ham with a black or red seal. That is where acorn-fed and grain-fed part ways. A cebo de campo pig stays on its plot all year, on an extensive farm or in intensive open-air rearing, with its ration of cereals and pulses and whatever it finds on the ground. A cebo pig raised indoors never reaches the dehesa. Mixing up these three is the most common mistake at the moment of buying.
| Rearing | What it eats | What it gives |
|---|---|---|
| Acorn-fed, in summer (dry dehesa) | Cereals and pulses, sparse grass, roots | The animal grows and builds muscle |
| Acorn-fed, in montanera (entry 1 Oct to 15 Dec) | Fallen acorns, fresh grass, roots, mushrooms | At least 46 kg gained, marbled fat that melts at a low temperature |
| Cebo de campo (outdoors all year) | Mainly cereals and pulses, plus what the plot offers | A steadier flavour, fat that melts less readily |
| Cebo (raised indoors) | Cereals and pulses only | No acorns, hardly any walking, little marbling |
What the law requires before you can write “bellota”
In Spanish law, acorn-fed ham has a precise meaning, and the word is not free to use. Article 3.1 b) of the decree defines “de bellota” as a fattening on the natural resources of the dehesa, with no supplementary feed. Article 6 and the annex then set, among other things, four conditions an inspector can check. They cover the entry and slaughter dates, the average weight of the batch on arrival, the weight gained over the time spent outdoors, and the number of animals allowed per hectare. If one of them fails, the piece drops out of the category.
| Requirement | Figure | Article |
|---|---|---|
| Entry into the dehesa | 1 October to 15 December | art. 6.3 |
| Slaughter | 15 December to 31 March | art. 6.3 |
| Average batch weight on entry | 92 to 115 kg | art. 6.4 |
| Minimum weight gain | 46 kg, over more than 60 days | art. 6.4 |
| Supplementary feed | None | art. 3.1 b) |
| Animals per hectare | 0.25 to 1.25 depending on tree cover | annex |
| Cebo de campo | Extensive farming or intensive open-air rearing, 100 m² per animal in the second case, slaughter at 12 months at least | art. 7 |
| Cebo | 2 m² per animal, slaughter at 10 months at least | art. 8 |
The space requirements apply to animals over 110 kg live weight. Royal Decree 4/2014, consolidated text, consulted 23 August 2026.
The last two rows are the ones to remember. In intensive open-air rearing a cebo de campo pig gets 100 m², while a cebo pig raised indoors gets 2 m², fifty times less. Space decides whether the animal walks, and walking is what works fat into the muscle. No label gives you that figure.
How many pigs a hectare may carry in montanera depends on its oaks. The annex allows 0.25 on the most open ground, where trees cover a tenth of it or less, and 1.25 once they cover over 35%. What that looks like on a real farm, in figures and on the ground, is in our article on what is a dehesa.
What to check before buying
A piece sold as “acorn-fed” without a black or red seal is held to none of this. The 46 kg, the 60 days and the dates do not apply to it.
Of everything you see when buying, the seal is the one element an independent inspection body stands behind. It counts for more than the title on the product page.
Three things you often read, and what the decree says
Three claims about the acorn-fed pig come up again and again, and the decree says otherwise each time.
“An acorn-fed pig eats nothing but acorns.” The decree speaks of fattening on the natural resources of the dehesa, which is wider than acorns. The animal also eats fresh grass, roots and mushrooms. That variety matters, because it gives the fat aromas that a diet of acorns alone would not.
“The montanera starts in September.” The earliest entry date is 1 October, and the animals must be in by 15 December. You will often read “September to February”, and both ends are wrong.
“Forty kilos gained is already acorn-fed.” The minimum is 46 kg, and below that the designation is refused. A range of 40 to 60 kg is sometimes quoted, and it is wrong too.
To picture what that takes, Ganadería gives around 600 kg of whole acorns per animal for a full weight gain over the season. In an average montanera a pig then puts on 500 to 600 g a day, and 800 g or even a kilo in a good year.
See it for yourself
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What it changes in the ham
Acorns change the make-up of the fat, and you can see it on the plate. Oleic acid dominates the fat of the acorn, and the pig stores it as it is, in its own fat. In an acorn-fed animal that fat contains at least 54% oleic acid, a reference figure, not a threshold set by the decree. Fat like that melts at a lower temperature than ordinary fat. On a warm plate an acorn-fed slice goes translucent in a few seconds, while a cebo slice stays matte far longer.
Walking counts as much as the menu. An animal that covers ground in the dehesa to find its food does not build the same muscle as one eating at a trough. The fat settles between the fibres instead of piling up in a layer, and that marbling gives the melting texture. Space is part of it. The cap on animals per hectare also follows the food, because a plot of dehesa only has so many acorns to give.
Curing comes afterwards and makes up for nothing. An Iberico ham of 7 kg or more must cure for at least 730 days, a shoulder for 365. Our acorn-fed hams come out at 44 to 48 months and our cebo de campo hams after more than 36. The cellar only concentrates what the pig ate. If you want the stages that follow slaughter, our answer to how is Iberico ham made goes through them one by one.
A simple test at home
Run two plates under hot water, dry them, and lay a slice from a different piece on each. On the acorn-fed one the fat turns glossy and translucent within seconds. On the cebo de campo one it stays firm and white for longer. You need no instrument to see it.
Four things to look at when buying
Four checks are enough, and none of them asks you to know the farm.
- Read the colour of the seal before the product name. Black and red mean montanera, green means cebo de campo and white means raised indoors. Our guide to serrano vs Iberico ham goes through the label seal by seal.
- Look for the breed percentage, which the label must show next to the name unless the pig is 100% Iberico. A red seal can mean a 50% or a 75% Iberico animal. Both exist, and they are not the same piece.
- Expect a price per kilo that adds up. An animal that had close to a hectare of dehesa for two months cannot cost the same as one raised on two square metres. Our article on Iberico ham price sets out ours, format by format.
- Give no weight to words like “natural”, “artisanal” or “from the land”. The decree defines none of them, and they commit no one.
Conclusion
Conclusion
It is all decided before slaughter
Texture, curing time, legal grade and so the price are settled during the autumn before. Salt, time and the cellar work on a material that is already set. That holds for the finest acorn-fed ham and for the plainest cebo.
None of which means you should always buy acorn-fed. The three ways of rearing answer different needs, and this is the order we suggest.
- Compare once, properly. Two 80 g packs served at the same temperature are enough to tell you which you prefer.
- Keep the acorn-fed ham for moments when it will be eaten slowly. What it has to offer lies in how its fat behaves at room temperature.
- Take cebo de campo ham for everyday eating. It strikes a sound balance between how the pig was raised and the price per kilo.
Taste it yourself
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Frequently asked questions
How many acorns does an Iberico pig eat in a day?
Up to around ten kilos. The journal Ganadería puts it at roughly 600 kg of whole acorns per animal for a full weight gain in montanera. Spread over the sixty-day minimum, that comes to about 10 kg a day, with wide swings depending on how much fruit is on the ground.
When does the montanera take place?
Animals enter the dehesa between 1 October and 15 December, and they are slaughtered between 15 December and 31 March (art. 6.3). These dates are not a rough guide. They follow the natural fall of the acorns and mark out the window in which a batch can qualify for the “de bellota” designation.
Does a free-range grain-fed pig eat acorns?
Its diet is mainly cereals and pulses, and the rules never ask it to eat acorns. In Spain that pig is called cebo de campo. It is defined by outdoor rearing, on an extensive farm or in intensive open-air rearing with 100 m² per animal, and by slaughter at 12 months at least. Whatever it finds on its plot is neither counted nor checked. The “de bellota” designation belongs only to pigs that gained 46 kg in the dehesa under the montanera rules. A cebo pig raised indoors has no access to acorns at all.
Why is oleic acid mentioned in connection with ham?
Because it is the trace the acorn leaves in the animal. It dominates the fat of the acorn, the pig stores it in its own fat, and analysis finds it there, at least 54% in an acorn-fed animal. It is also what makes that fat melt at a low temperature, and so what explains the texture of the ham. We draw no health claim from it.
Sources
- Royal Decree 4/2014, consolidated text published in the Boletín Oficial del Estado. Article 3 (designations and breed percentages), article 6 (montanera dates, weights and weight gain), articles 7 and 8 (cebo de campo and cebo), article 9 (seal colours), article 12 (minimum curing times) and the annex (animals per hectare). Consulted 23 August 2026.
- A. Mateos San Juan, “El cerdo ibérico. Factores que influyen en el crecimiento y en las características de la canal”, Ganadería, archive of the Spanish Ministry of Agriculture. Acorn intake, weight gain and oleic acid. Consulted 23 August 2026.
- The curing times of our own pieces come from the LOLO Jamón catalogue, checked on 23 August 2026 and again on 29 October 2026.
Read next
- Best ham in the world, with the designations compared
- Serrano vs Iberico ham, and what the breed percentage means
- What is a dehesa, and how much room the pigs really have
- Best pig in the world, and what the texts say about the breeds
Written by
Valentin & Pablo
Founders of LOLO Jamón
We select our pieces in the drying cellars of the Salamanca dehesa, and we filmed a full montanera season for our documentary Viva España.
Our pieces from the montanera
Acorn-fed 100% Iberico hams and shoulders from the Salamanca dehesa, cured 32 to 48 months depending on the piece. In 80 g packs or as a whole piece.
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