I'm a little late to the conversation, but I think a lot of sour beer brewers have come around on the thought that you need to leave food for Brett to produce it's typical flavor profile. If the appropriate flavor precursors are available, Brett will happily metabolize these without needing a significant carbohydrate source.
I heard a recent interview with Allagash where the brewers stated that they mash low to try to get their primary fermentation to finish as dry as possible when they're planning on adding Brett to the secondary. This lets them bottle a batch much sooner since they don't need to wait as long for the Brett to get close to terminal gravity. Their Brett beers are fantastic, so they must be doing something right.
This is not what Russian River recommends. They say the opposite (for Supplication). And I guess they also must be doing something right.
I can't get RR up my way. Send me a bottle and I'll see if I agree with you
I'm not saying that you shouldn't leave complex carbohydrates behind for Brett, just that you don't need to.
...Brett will happily metabolize these without needing a significant carbohydrate source...
This is the answer to the thread subject (at least for Brett).
Brett doesn't need a carbohydrate (sugar, dextrin) source to contribute flavor.
Brett needs carbs and oxygen for growth, so if you pitch a small amount in secondary it may take longer to get to the desired flavor profile. Obviously other factors play into the rate of flavor contribution, i.e. temperature, competing organisms, pH, etc. etc.
Pedio does need a carb source to produce lactic acid, but most strains can break down complex starches leftover by sacch fermentation (and even some left by Brett).
Adding 'food' (sugar, dextrin) to secondary will really just result in more alcohol from fermentation by brett.
Good points. This is why I don't like to pitch straight from dregs or a WL vial without making a starter. I'd rather pitch a bigger cell count of healthy cells. There's some old thinking out there that Brett is like the Mad Max of yeast, and you should subject it to harsh conditions to get it to thrive (i.e., low cell counts). In reality, it's like any other yeast - treat it well and it will treat your beer well.