The example of my latest revelation: I had read, or maybe just assumed, Bittering hops were just for bittering. As long as you hit the required Alpha Acid level which itself will offset the sweetness of the malt to the right degree, your beer will be balanced. From this i extended my assumption (from reading....) that as all flavour and aroma is lost, you can more or less use any high alpha hop for bittering - the flavours are boiled off and its just...bitter. Of course i failed to consider the fact that if this was the case there probably wouldnt be so many options of bittering hops, and just one standardised, mass produced, cheap product that everyone used for everything. Ah....hindsight.
In addition to this i have a book which handily contains a chart of 'hop substitutions' - Hops similar to each other - useful in a pinch but (only now i consider...) it doesnt state exactly how these hops are similar - or for what purposes - flavour/aroma? Bittering? AA levels? Cone Shape? Geographical origin? - Valid reasons for comparison but in some cases absolutely no help when it comes to the end result.
I should mention here that i have a tendency to bodge things, mainly due to some deep set desire to save money, in this case by substituting ingredients so i dont have to keep stock of everything and assuming the end result will be the same... and partly because i have next to no forward planning skills, and very little patience, so even if i did order up the right ingredients i'd probably get itchy feet and start 'substitute brewing' before they turned up.
I digress. In this case my 4 Shades of Stout Recipe requested Cascade hops for bittering. A curiosity i thought because these are known for their citrussy aroma additions in american IPA (or is it APA now?). I didnt have any (surprise!) but thought as it was just for bittering a 'similar' hop with alpha levels scaled for the same bitterness would suffice. Out comes the book - somehow i ended up at Perle. I knew nothing about Perle - infact Tom's intention to put it in a Lager is the only reason i had any stock. I probably should have looked it up. Ah...hindsight again.
Last night: 3 weeks in the bottle and we have results. A near perfect stout (if a little young...) in body, colour, roastyness, mouthfeel. Finally a success after many substandard stouts! And that bitterness that lingers on the tongue... its like... Air. Like clean, almost minty air. Like drinking distilled water. Is it unpleasant? no. Is it right? no.
Oh well, its all a learning curve.