This page provides a good summary of technique and the following warning:
They also recommend that manures and manure teas not be applied to vegetables and fruit within 60 days of harvest and 120 days to harvest on root crops.
I personally wouldn't use store bought manure. I'd either get it from a source where I knew it was well composted, or do it myself.
I've done some more research on this (important!) question.
Presence of Pathogens
This article (which is pretty technical) discusses compost production techniques. There are some references in there that mention certain techniques that will increase the likelihood of getting pathogens in your tea; it makes sense to avoid these. (It mainly sounds like you want to avoid adding "enhancements" to the tea, but you'd need to read the referenced articles for details.)
Compost (incl. Manure) Quality
This fact sheet from Cornell talks about compost production standards. Executive summary: unless you're dealing with human sewage (sludge) or using compost that is specifically regulated by the National Organic Program, it's essentially unregulated. (That fact sheet covers NY state; I suspect but am not sure that other states have similar situations.) Why it matters to you: you have no idea what was done to produce the stuff in the bags you buy.
This article gives you a feel for how much effort you can put into determining whether the end product of a composting process is useful.
Starting with a product that already has a high pathogen load seems like a recipe for disaster.
Tea Production Technique
From what I've seen in scanning the literature, there are various techniques in use for producing compost tea. I've seen people ranting (not hard science) that one technique is vastly better than another technique. I'm not bothering to link to any since I think I've seen arguments in both directions and it's impossible to tell who is right.
Some of the studies I've referred to elsewhere here talk about maintaining different temperatures. (They're all held at controlled temperatures, of course -- most home gardeners wouldn't bother.) It wasn't clear to me whether one temperature is better than another; there could be differences depending on what you're trying to do with the tea.
One of the major differences in production is the use of aeration. This basically involves putting a pond pump or something similar to get air into the tea. There are descriptions of systems you can set up with an aquarium pump for small scale production.
Benefits of Compost Tea
There is some scientific evidence that teas are effective at reducing disease pressure. This article refers to some other scientific publications (that I haven't located yet) about tea effectiveness at fighting disease.
But there are scientists cautioning the use of manure teas. It's not a miracle cure. As you discovered the hard way, there are risks too.
For home production in an uncontrolled setting, it may not be worth the risk. Personally, I like the idea that I could make manure tea and possibly reduce the chance of getting blight on my tomatoes. But I'm not sure that I can produce tea in a way that will really give me the outcome I'm looking for, and mitigate the risks.
Unfortunately I haven't really answered your direct questions:
Anyway, I'm just wondering what the proper setup is for manure tea, should it be done in the shade? how fast should you use it? do you need to clean the barrel after using it? What is a good store-brand manure to use? How can you be absolutely sure the manure is fermented before using it?
- There are different setups possible for tea, and it isn't clear that there is any one "proper" setup. The literature doesn't seem to have converged on a best way to do it.
- I didn't see any mention of shelf-life...
- Being scientific studies testing for pathogens etc, the studies I saw were sterilizing the barrel. It isn't clear that you need to go to this length.
- See "quality" above regarding the difficulty in choosing a brand and knowing its quality.