I recently purchased 5 - 1 gallon primary and 1 gallon secondary fermenters. I did this so I could try 5 different mead recipes at once. I'm now thinking once those meads are finished this will be fun to brew with. Anyone see any reason not to brew up a 5 gallon batch of stout and split it into 1 gallon individual batches: regular, coffee, coconut, vanilla, and maple. Also thinking it would be fun with milkshake ipa: regular, pineapple, raspberry, strawberry, and blueberry. Seems like this would be a way to maximize each brew day and if I find one I really love I could always make a 5 gallon batch of it later. Anyone doing this already and have tips?
If those fermenrers are only 1 gallon each, 5 of them won't have enough headspace for fermenting 5 gallons of wort.
I did it one time with a big RIS, I found bottling (and keeping separate) 4 different 1 gallon beers to be a huge pain in the ass, never did it again. After that, the smallest batch I would bottle is 2.5 - 3 gallons.
If you do a search of this forum you'll find threads that discuss small batches. It will be interesting and fun for you to try different flavorings, but like @VikeMan said, you'll not have any head space if you put 5 gallons into 5 1-gallon fermenters. Get a 6th fermenter for the excess wort or brew 4 gallons to be split into the 5 fermenters.
With this project, you wouldn't have to ferment any of the variations except for the maple, so you really don't need to split the batch, unless you're planning on using the actual product. You can just dose a certain volume with the additive in question. This certainly would be neat. Might I suggest using a juicer, if you have one, or just using juice from the store?
I've done it a few times including a Smash pale ale last month that I used 3 different aroma and dry hops (Sabro, Belma, and Idaho Gem. Just tried 1st bottles saturday and really dug the Sabro batch). Like @wspscott says the bottling can be a pain in the ass so I couldn't see myself doing it more than a couple batches a year. Lately I've gotten more into adding stuff to the last gallon at bottling. Makes for some fun experiments with very little added work. No reason you can't do it just make sure you have the headspace in your fermentors. Might be tight especially if you are planning to add real fruit to the milkshake batch.
I was only brewing 1 gallon batches until about a year ago when I scaled up to 3 gallons so I could start kegging my hoppy beers. One of the added bonus's has been with my wild beers. I'll brew 3 gallons of a mixed ferm saison, let it go through primary, then rack onto different types of fruits, herbs, spices etc. I love doing it. Like you said, it maximizes your brew day and lets you experiment in small doses. I recently racked a 3 gallon batch of Flanders red onto raspberries, cherries and tempranillo grapes. Fingers crossed.
I love split batches. I really don't like drinking the same beer over and over and I like to experiment in small scale. Split batches are awesome to change up yeasts, adjuncts, dry hops, etc. It does make bottling a little more involved and tie up fermenters, but it's worth it. My next IPA will be split 3 ways with 3 yeasts I've never used.
Ill split 5 gallon batches, usually a 4:1 split, as this is an easy way to get into blending beers. For example, ill sour 5 gallons, transfer 4 gallons onto fruit, save 1 gallon unadultered. After a few rounds (takes a while in this case), soon i have several different 1 gallon brews to blend together. Pretty fun stuff! Could see this working with big stouts as well.
Sometimes I'll split 6-7 gallon batched in half. Usually for different wood, coffees, nibs or hops. Nice to have variety.