Use this to cook barley, wheat and malt from raw through to light roasted, medium roasted, dark roasted and finally to burnt. Any type of barley, wheat or malt may added or removed at any stage of the process, and you can refire the oven without effecting it's yield. The Grain Oven is a pretty user friendly piece of equipment.
The oven will not operate if it is loaded with more than 1000 debens total of barley/wheat/malt and wood. But you can store up to 1000 wood and infinite amounts of any type of barley, wheat or malt in it. Given the low building cost, it might make sense to build two, one for roasting and one for storage.
The Grain Oven burns 5 wood per tick, moving roughly 10% of the barley/wheat/malt from one state to the next, apparently with a random selection of which 'pieces' of barley to cook (advance one stage). It is generally best to cook large quantities of barley, wheat and/or malt at a time, as small batches may require several ticks to show any progress at all. A maximum capacity run of 700 barley, wheat and/or malt, plus 300 wood, will produce a fairly even spread of light through burnt roasts. If you have plenty of Barley/wheat/Malt, you're better off going too dark rather than too light, as you can quickly obtain more of the light roasts, while the dark roasts can take a while. You can remove or add any type of barley or malt at any time during the process. One way to get a large amount of a certain darkness it to continually remove any barley or malt that gets to that darkness, while adding more lighter barley, wheat or malt.
Or to put it another way, if you're going for a specific amount of something, start with more raw than you need because the last few grains take forever to cook, and burn wood all the while.
Built: in a compound, uses 7x7 cells
Skill/Tech required: Barley Cultivation