How to reserve barrels for drink?

My fortress is overflowing with food barrels, but there is very little drink left. I do have seeds for brewing more, but cannot, since there are no more barrels. There is no wood available for making more. What can I do?

You can also make barrels out of metal (at a forge or magma forge by a dwarf with metalsmithing enabled), and in recent versions you can also make large pots out of stone (at a craftsdwarf's workshop by a dwarf with stonecrafting enabled).

To set a number of reserved barrels, hit p to bring up the stockpiles menu. On the right, about half-way down, you'll see the number of (fortress-wide) reserved barrels. The keys to change the number of reserved barrels are shown after the number of barrels currently reserved, use * to increase the number, / to decrease the number. I personally recommend reserving at least 20.

If your number of empty barrels drops below that, barrels will not be used for storing dry goods (seed bags, plants, meat), they'll only be used for jobs that require barrels, such as brewing.

If you're running low on barrels for brewing, the best solution is usually to make rock pots, by enabling stonecrafting for one of your dwarves, and selecting first rock then make rock pot at a craftsdwarf's workshop.