I may have missed this: is the world straight-up Sci-Fi, or is it Sci-fant?
Fortunately, that's pretty simple... grind the source down to fine particles, put in boiled water, let cool to under 100°F add yeast, and keep between 60°F and 90°F for a couple months, covered but vented. If using wood, you want sawdust, really... but don't taste test it! straw, chaff from wheat, and a number of other items can be used to make a boiled mash, which, once cooled, can be fermented easily. Some plant matter that doesn't easily break down can be allowed to generate molds to render the starchews to sugars for fermentation.Very good.
One issue that few post-apoc settings takes into account is that nearly all shallow-deposit resources have long since been exhausted, making salvage the only source for metals. Fossil fuels will be limited without heavy equipment and infrastructure; coal could be obtained for a while from existing mountain-cropping, but oil and natural gas won't be available a couple years after a fall.
That would make data on producing grain and wood alcohol vital, as they are the only real fuel that will be available a generation past the fall.