received some yeast: spots on a petri dish... what next?

[ebbelwoi]

A microbiologist acquaintance shared some of his work with me today. He gave me a petri dish with yeast (S. cerevisiae) that he had extracted from cherry blossoms and isolated in his lab.

Obviously, I'd like to brew something with it. He says his lab only uses a special solution to propagate its yeast, and has never tried any commercially available products. He said he could give it a shot, but I'd like to see if there's anything I could do on my end as well.

There's really not much in the dish. It looks like a light dusting of mold, in terms of quantity. Does anyone have any suggestions as to what to do next? I don't have any lab equipment or supplies. The most "scientific" thing I've got is probably yeast nutrient.

 

[bucketnative]

Feel free to ignore what I wrote below... Braukaiser has it right here: http://braukaiser.com/wiki/index.php/Growing_Yeast_from_a_Plate - You can use a sanitized spoon instead of the inoculation loops that he suggests.

If it were me, I would start with 250 mL of wort at 1.020, lightly hopped to minimize contamination effects from the home environment. I would also do three separate vessels of starter wort to, again, give me an improved chance of success. Sanitized jars will work in the absence of stir plates and Erlenmeyer flasks. Try to minimize contamination (as much as you can in a home environment).

Inoculate the starter wort with a few of the colonies. Use a sanitized spoon, or other implement, to scrape off some of the colonies (spots on plate) and deposit them into the wort. Your wort is your specialized solution (growth medium). Let the yeast grow in well-aerated wort (follow some of the guidance in yeast capture threads here on HBT).

Then step up your starter, both in terms of gravity (maybe, 1.020 -> 1.030 -> 1.040) and volume, again following guidance on yeast starters and propagation, here. Sample the wort after decanting at each step to determine if the yeast is producing a palatable product.

 

[RPh_Guy]

He gave me a petri dish with yeast (S. cerevisiae) that he had extracted from cherry blossoms and isolated in his lab.

Obviously, I'd like to brew something with it.

Do you know whether it ferments maltose and maltotriose? The large majority of wild yeasts do not, and so it will probably give a poor attenuation, around 25-50%.

 

[ebbelwoi]

Thanks for the detailed advice! I'll give it a shot this weekend. Do you recommend adding any yeast nutrient at any stage?

 

[IslandLizard]

A stir plate or orbital shaker is useful to keep the starter agitated and aerated for faster and better growth. Maybe your friend has a decommissioned one. You can build your own stir plate too from a computer fan. Or build 2 or 3.

Especially later in the growth process, without constant agitation, watch out for overnight eruptions. Many a time I lost half the culture to the countertop that way, having to start them all up again. Ample headspace helps, but not always.

Also look up making "shaken-not-stirred" yeast starters. They're a good alternative to stir plates or shakers, but need some periodic attention.

Wort should have all the nutrients required, but a small dosage of nutrients can be added, sure. Just be careful not to use too much, especially DAP. More is not better, and with weak and small starter volumes, it's easy to overdose.

 

[ebbelwoi]

Thanks everybody, for the advice. The starter seemed to work out. I've gone from 200ml to 2.5L, and am now drinking some of the poured-off starter. Seems good enough to go for a proper 5L batch. Attenuation seems quite good (no sweetness) and it seems to flocculate pretty well. Looking forward to round two!