easiest solution: make big prepared food stockpiles that don't take barrels. make sure no other food stockpiles take prepared food
then at the depot, press "g" to move goods, then while selecting "All", use "s" to search for "roast", and you can order the roasts to be brought to the depot. (assuming you only cook lavish meals).
Although I do this too, there's a main issue of space and hauling dozens of roasts to the depot, the reason I think the OP wants to use metal barrels to store food is he wants to efficiently store his roasts, move them quickly to the depot for trade and to trade with elves that otherwise would get touchy if you try to sell them roasts on a wooden barrel...
the most efficient solution for storage space is obviously a quantum stockpile, that can be easily set up by having the kitchen give its roasts to a small "output" stockpile and have a route draw all the prepared meals from the output-pile into a minecart stopped on a track stop set to auto-dump on a 1-tile quantum pile
There's a major drawback for the quantum pile when it involves food items: FLIES, yes flies roam food that isn't in a container and keep annoying your dwarves and giving them bad thoughts... it does add up, believe me...
Another drawback is that your dwarves will have to haul individual roast large distances to the depot...
The solution I came up was using minecarts for storage instead of barrels and pots, you only need a route, a stop, linking to the output-pile, assign a minecart to your "meal" route and the roast will simply accumulate inside the minecart, your dwarves will get roasts to eat from the minecart, and there's no flies
optionally you need an auto-dumping track stop right next to your Depot, set up an empty route with a stop on it, and a 1-tile quantum pile accepting the auto-dumped meals.
when the caravan arrives, you assign the minecart full of roasts from your "meal" route to your "depot" route, a dwarf will haul the minecart with all the roasts to the stop at your depot, empting it on the quantum pile, from there your dwarves can haul the roasts to your depot very quickly...
this allows you to trade only the roasts, no need for containers, you store efficiently flies-free and move the roasts quickly, alternatively instead of dumping the roasts right next to your depot you can trade the whole minecart with all the roasts inside, notice that this way, like it happens with barrels and pots you can't trade individual roasts within the containers, only the container with all roasts inside, but using routes you can specifically select which minecart you'll be using to store your roasts in your "meal" route
the only drawback to this method is that you need to set a "meal" route for each minecart that you want to use as a container to store roasts, this only in case that you run out of space in your first minecart and need to keep on producing and storing more roasts, fortunately a single minecart can store large amounts of roasts, enough to buy out an entire caravan and keep your dwarves feed so not a big deal to set up a second "meal" route in a large fortress.
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Topic: Specific barrel use (Read 2050 times)