ikyn, I hope you don't mind that I answer your PM and the above question here.
My current run of yeasts has been harvested off of some uncrushed 2-row malt. Basically, I threw them into a tube of 1.040 wort and let them ferment. At days 4, 10, 20 (and soon, 30), I withdraw a small amount of wort and plated it out on beer-agar plates. 2 days later I had colonies, like in my example image above. No dyes were added to the plates - Rhodotorula is naturally pigmented. About the only thing I had in my plates that is unusual was a bit of penicillin and streptomycin, to inhibit the growth of any bacteria (I'm after wild yeasts, not wild anything). The plates themselves are 1.002 gravity wort + enough agar to make them hard.
For fruit, your best bet is to dip uncrushed fruit in sterile wort and ferment whatever comes off of the skins. Even on fruit, the density of yeast tends to be a little low, so simply streaking on an agar plate may not get good returns. By growing in wort first you'll enrich the beer-compatible organisms, which can then be selected for by plating.
As for a step-by-step guide, that is in progress - I'm writing up the current stage of my wild-yeast hunt, and that post will include inoculating, plating and selecting yeast strains. That should be out late next week. Later in the summer I'll have a follow-up post, looking at the fermentation characteristics and identification of the yeasts I've purified. I don't know when this one will be posted - between holidays and preping the lectures for a new course I'm teaching in the fall, I'm not going to have much free time over the summer.
As for identifying yeast strains with dyes and whatnot, that is not easy. There is no singular dye or other compound that allows you to identify in one step what a yeast is. Typically, you need a number of specialized dyes and plates to ID a species; basically, you look for the ability to survive certain antibiotics, grow on specific carbon sources, and incorporate (or degrade) specific dyes. For example, brettanomyces will grow on a plate containing nothing but cellbiose and yeast extract, is resistant to cycloheximide, and will degrade the dye bromocresol green. To be able to ID the ~20 species of yeasts you may find in a wild ferment is prohibitively expensive, requiring a number of selective medias, antibiotics, and dyes. A good resource for this is "Yeasts, A Taxinomic Study". Every species of yeast, what it looks like, what media it grows on, etc, is outlined in this book. Its also a $500+ book; your local library may have a copy, otherwise a partial copy (with most of the brewing yeasts in it) can be found at google books.
A few bloggers out there have come up with some doable-at-home yeast analysis systems; you may not get a specific match, but you will be able to separate brett from sacch, which are the two kinds of yeast we're usually the most interested in. For example:
The methods these guys have written up tend to work better for pulling wild yeasts out of labmics (or a completed wild ferment) than they are for pulling out yeast from a wild source. Basically, the 1-3 year ferment of a wild brew acts as a powerful selection process, leaving only a few species of yeasts (brettanomyces and saccharomyces) and bacteria (lactobacillus, pediococcus) alive. If you're looking at a fresh source, there are dozens of species present at any particular time.
In my case, I'm taking a more technological approach (sequencing a small part of the genome) to ID my yeast. I'm not IDing all of them - I'm only IDing the ones which make OK beer or have a unique character that I might want to include in a mixed fermentation. My method of identification is quite a bit cheaper than the classical media/dye/antibiotic approach, if
you have access to the equipment (which is expensive). I run a research lab in a uni, so I have access to all the toys. Obviously, this isn't stuff the average guy has in his garage.
My advice would be:
- Soak some intact fruit in 1.020 to 1.040 wort (with moderate hopping, if you desire) for 12-24 hours. Remove at that point (as sterilely as possible), and let ferment at least 20 days. This should give you a Saccharomyces-dominated ferment, with most of the oxidative yeasts and nasty bacteria killed off.
- At the 20-day mark (and if you want, every 10 days thereafter), plate out a tiny amount of the ferment - a single drop is literally too much. You should end up with single colonies. Pick individual colonies - ignore anything pigmented, as those are usually nasty yeast or nasty bacteria.
- Grow each colony up in its own tube of wort (a few ml or wort is all you need). Store in the fridge, or freeze using wort + 20% glycerol, until you're ready-to-roll
- Sanitize a bunch of beer or wine bottles, make a bunch of foil caps to cover the bottles, and sanitize those as well. Brew up a batch of mild-tasting/lightly hoped beer and split it into the bottles (100-200ml/bottle for beer bottles, 500ml/bottle for wine bottles). Innoculate each bottle with one of the strains of yeast you purified, cap with your sanitized foil (AKA your airlock), and then let ferment 2 weeks at 20C/70F. Make sure you hold back a little bit of each yeast sample.
- Taste them, and decide if they're any good. Throw out the tubes of the nasty ones, bank the good ones as you see fit.
- At this point, if you want, you can make some of the media described in the blog posts I linked to, in order to identify the species of yeast you purified.
As for a source of all of these things, I'm not sure - I'm a Canadian, and get it all from BioShop Canada. They do ship to the US, but I imagine a US-side company would be cheaper. I'm also not sure if they (or their US equivalents) will ship to private homes; chemical companies are a little paranoid and liability-adverse. Those blogs I linked to are all US-based; they may mention where they get stuff from.
In all likelihood, the above process will lead mostly to Saccharomyces or Brettanomyces. You can separate the two of these using bromocresol green (Brett eats it, so when grown on a plate with it, bretts are white-to-yellow in colour; sacc turns blue-green). Identifying the specific species of brett or sacc is much harder, and would require more specialized dyes/medias, as described in the book I linked to above.
Hope this long rambling post sheds a little light...