Already swelled packs probably full of long dead yeast as well as a few live ones.
Make a beer taste like sh!t in most cases.
I hadn't considered this. The yeast smelled okay upon pitching into a starter, but in several cases it acted strange e.g. extremely active or inactive fermentations, odd odors during fermentation, etc. These packs were not simply a little puffy...they were swelled almost to the max, and the nutrient pack was still intact (I was either able to pop it or was able to see it when I emptied the package into my starter). However, the beer does not have any kind of rubbery flavor to it. The most frustrating thing is that I can tick off a list of off-flavors that are NOT present in the beer more than I can describe what actually tastes wrong.
More details! I want to see a couple recipes, know more about your process, etc.
I'm with the others who think "too complicated of a recipe" when they hear muddy.
I have been using recipes from Brewing Classic Styles, and all of my duds have actually been repeats of previous successes, so I doubt that the issue is with the recipe.
Could be the yeast, are you checking viability and making starters for each beer with Mr. Malty or Yeast calc.? If the beers are properly fermenting and attenuating and you are not getting hot fusels or other fermentation related issues I'm not sold on it being the yeast.
I use the Mr. Malty calculator. I have tried making starters both with a stir plate and with intermittent shaking. Neither approach has made a difference.
Have you tried to start with 100% R/O water with calculated additions via brun' water? Have you changed suppliers of your ingredients?
I brew with RO water. My tap water is pretty much liquid dry-wall, so it's not well-suited to brewing. I have made adjustments in the past with Palmer's spreadsheet. I was always successful, for the most part, but I stopped making adjustments when my product began to go south, just in case I was over-adjusting the mineral additions.