Identifying yeast strains

[weagoodall]

Anyone here familiar with using agar plates and cultivating wild yeasts? I’ve attached some photos of three semi successful agar plates (my first attempt) using a wild yeast starter from my back garden on the northern outskirts of Glasgow. Now I’ve tried searching online as to how to ID decent yeast strains but I’m struggling. Any one able to give me any pointers or advice? I’m aware the nasty green fungus isn't right but would love to know what everything else on these dishes is. Especially the big white blob.

 

[prog99]

85 pages on the subject here although it does drift off from time to time - Isolated Yeast (Tree House): How to Identify and Characterize? Would suggest a lot more than just an eyeball.
@Northern_Brewer comes across as knowing his stuff.

 

[Northern_Brewer]

Just looking at them gives limited information - this gives you an idea - it also shows you how to streak to ensure single colonies, About the morphology of colonies (and there's lots of good info there on "home" microbiology).


Those moulds will always grow faster than your yeast, you want to restreak them if possible.

In a lab the first thing you'd do would probably be interdelta PCR (as in that Treehouse thread), but assuming you don't have a molecular biology lab to hand (unless you can ask a local university lab?) then you can do a certain amount of brew-testing.

Make up some wheat-beer wort (say 30-50% wheat) and hop it to "fairly hoppy" levels. Then split it into sanitised jam jars, one for each of your new yeast plus a phenolic and non-phenolic known yeast as controls (say Munich Classic and US-05/Wilko/S-04 etc). Measure the OG, you want somewhere in the 1.040-1.060 range. Then let them ferment at normal ale temperatures, high teens C.

Then sniff them, and measure the FG.

Your phenolic control should have typical cloviness - and a number of your test ones will as well. Whether you want to take them further is up to you.

The FG will allow you to work out the attenuation, which will give you an idea of whether they're going to be any use to you in brewing.

 

[weagoodall]

Just looking at them gives limited information - this gives you an idea - it also shows you how to streak to ensure single colonies, About the morphology of colonies (and there's lots of good info there on "home" microbiology).


Those moulds will always grow faster than your yeast, you want to restreak them if possible.

In a lab the first thing you'd do would probably be interdelta PCR (as in that Treehouse thread), but assuming you don't have a molecular biology lab to hand (unless you can ask a local university lab?) then you can do a certain amount of brew-testing.

Make up some wheat-beer wort (say 30-50% wheat) and hop it to "fairly hoppy" levels. Then split it into sanitised jam jars, one for each of your new yeast plus a phenolic and non-phenolic known yeast as controls (say Munich Classic and US-05/Wilko/S-04 etc). Measure the OG, you want somewhere in the 1.040-1.060 range. Then let them ferment at normal ale temperatures, high teens C.

Then sniff them, and measure the FG.

Your phenolic control should have typical cloviness - and a number of your test ones will as well. Whether you want to take them further is up to you.

The FG will allow you to work out the attenuation, which will give you an idea of whether they're going to be any use to you in brewing.

Very useful link there, thank you. I didn’t think I did too badly for a first attempt. I’ll go back, start again and streak properly. I suppose, realistically, I’m unable to determine the actual strain unless sending it to a lab. I’m going to keep trying the Petri dish yeast gathering and just go ahead and make a spontaneous ferm brew and hope for the best. Have you done one before?