I think there's a few routes to take here.. either go for a more generic "food" resource and forego explaining it (the easy way out) or players will have to wait with the actual conquest until they know how the aliens' food industry/metabolism work (could be researched, perhaps? But that implies capturing aliens, performing autopsies and whatnot..Or peaceful observation ;) ).

"who knows what might happen?"

Hehehehe. That was EXACTLY the clip I thought of as well :-)

Seriously though; there's decent evidence that amino acids (what we need proteins for) and sugars are pretty common chemicals and can even form naturally in chemical clouds in space in quantities we can detect from a thousand ly away. Conway Morris argues in a couple of his books that this would imply alien life a) will exist (because the materials are readily available) and b) will be made of much the same sort of stuff as us, and presumably therefore will have similar basic dietary needs.

Note, however, that even on earth many life-forms are incredibly intolerant of even small changes to their diet. Pandas live on particular species of bamboo and won't eat anything else. Sheep can be poisoned by being moved to fields with grass they're not used to... apparently they're very sensitive to trace metals contents.

So while it might be possible to synthesise the right foods from materials, the actual food isn't likely to be very portable.

The mood of the game is a homogenic empire, not a federation. Aliens are at most second rate residents (pay poor taxes, do not add to recruits pool, work inefficiently, happiness of aliens living in the player empire does not even add to imperial pops happiness), the player want the planets not for the alien population but for the territory & infrastructure. Ideally, I don't want the player to think too much about the alien scum living on the planet he/she conquered.

So, I worry that if I start simulating it more detailed (like food types for aliens) it would refocus the player's attention to the aliens pops... While the focus should be on Terrans.

Therefore some simplier solution would be ideal...

and there will be enough food for everyone

I don't want there to be enough food :) That's boring. Plagues of space locust that halves crops for X turns, hunger riots, etc. That's the theme I'm after.

Food is an important limiter of Terran pops (natural growth rate is high), it being used up by the mostly useless alien pops messes up with the concept.

Although modern "Terran agriculture" is simply transforming fuel to crop and there are options like greenhouse and hydrophonics, if you intend not to involve that mechanic, I think options left are different foods edible by different races as you mentioned or a reason that Terran crops can't grow on this new planet.

I don't want there to be enough food That's boring.

If not enough food is the conflict that you want to have, then is your question how to "solve" it, or how to "resolve" it? (By "it" I mean the Terran disgruntlement over not enough food, given that the native species is also eating.) Are you looking for something to give the players to use when their Terrans rebel? Or are you looking for interesting wars? I still don't get what you're asking.

I don't want the player to think too much about the alien scum living on the planet he/she conquered.

That's the real problem, then. The Terrans are the aliens, and if they're upset about not having enough food, they can darn well leave and go conquer another planet. Or find one that isn't already inhabited, so they can have all the food to themselves.

Start over. You want Terrans to conquer planets. You want them to regard the native "scum" as a resource, to use as forced labor or cheap labor or something. You want the Terrans to get disgruntled because there isn't enough food on the planet to feed both the native "scum" and the conquering Terrans. That's all fine (you can have all that). What's the problem you want to solve now? You have what you want, don't you?

correct me if this is wrong:

1. terrans conquer planet A. planet A's food now comes from terran empire, not the old owner.

2. aliens still on planet A + new terran colony on planet A = more food than planet A gets from terrain empire.

3. exiting civil unrest modeling of lack of food automatically causes terrans on planet A to rebel. - thus the problem.

man, this ones easy!

obviously, as conquerors, terrans get first dibs on food!

• War gives the right of the conquerors to impose any conditions they please upon the vanquished. , Gaius Julius Caesar

so you need to adjust your modeling of civil unrest due to lack of food.

food going to a planet should go to terrans first, any extra goes to other alien populations still there. and aliens without enough food should starve.

that way, only when the empire cant even feed a terran colony will that colony start to starve and rebel.

Got an idea, maybe consume the food not globally but per planet? So, first a planet would get X food from the imperial stockpile and then all pops there (Terran and aliens alike) eat it. And then you could give edicts like "planets with more than 50% alien population have food allocation halved" or "the capital planet gets +25% extra food".

food going to a planet should go to terrans first, any extra goes to other alien populations still there. and aliens without enough food should starve.

There is no such thing as "extra food" in the game. They eat everything available (except some extremelly rare cases where you have more food they can eat which will basicly never happen). I mean, there is no 0/1 food consuption like in most games. There are stages of food availability (scarce, too low, adequate, good supply, extra rations, feast) which affects the population growth and happiness.

So, it would mean all aliens starve in one turn, always :) It would not fit the game's mood and mechanics (the aliens as the second grade citizens are still a bit usefull).