While many of my readers reply directly here on my blog, I do get the occasional email asking questions in relationship to some of my posts. While a lot of these are simply requests for clarification, some are seeking details missing from posts, questions expanding on posts, and requests for posts/videos.
I’ve compiled a bunch of questions from various emailers, and answered them below.
Questions are divided by category:
- Mailing Yeasts
- Wild Brewing
- Yeast Wrangling
Q: How well does this really work?
A: People don’t seem to believe the posts where I describe a 100% success rate, but that is effectively what I have. To date I have mailed out 135 yeasts, and received 71 in return. Of these:
- One of the yeasts I received had a bit of a mould contamination, which I was able to remove
- One of the yeasts I sent had a mould contamination, which the brewer was unable to remove
- Only bacteria (likely lactobacillus) was recovered from one mixed culture I sent
|This envelope contains dried and inactive brewers yeast sterilely deposited into protective foil envelopes. These yeasts are being shared between hobbyist home brewers and have no commercial value.
These yeasts are not hazardous to humans, livestock or plants.
Shipment of these non-hazardous organisms is not regulated under the UN’s Recommendations on the Transport of Dangerous Goods, nor under the transportation acts of the sending or recipient countries.
Q: Are you still isolating wild yeasts?
A: Yes! However, I have given up on deriving yeast off of malt as every yeast I’ve pulled off malt (3 attempts now) has been shack-nasty. I’m planning on harvesting some from the garden this spring, and have a couple wild ferments going off of some fruit. I hope to be able to pull a few useful strains out of these attempts.
Q: How come you don’t distribute any of the wild yeasts you isolated in your previous blog posts?
A: Because, to-date, they all suck.
Q: Can I get some Rhodotorula?
A: I’ve had several requests for Rhodotorula (the bright red/pink yeast isolated in one of my yeast hunts). I’m not sure why – I don’t think it would ferment. Regardless, the answer is a firm ‘no’. Some Rhodotorula are biosafety level 2 pathogens and its not legal for me to send them to non-BSL2 labs.
Q: If I send you a wild yeast, can you identify it for me?
A: If it makes good beer, yes.
Yeast wrangling questions:
Q: You use antibiotics to control infections in some of your yeast cultures. Do I need these?
A: No antibiotics are required. I use antibiotics to help clean up potentially contaminated yeast sources, but so long as you start with clean yeast, or streak out your yeast and collect pure colonies, the antibiotics are completely unnecessary.
Q: I got antibiotic ‘X’, how much do I use?
A: It depends on the antibiotic. Antibiotics tend to be sold either in international units/ml or mg/ml. If you google your antibiotic and “agar plate” you should find blog posts which describe the amount to use. If you can choose I’d recommend streptomycin, as it has good activity against gram negative and gram positive bacteria. Many will get penicillin, which doesn’t work against gram-negatives, but will will lacto and pedio. 100 to 200U/ml of either (or both) of these works well.
Q: Why do you make your plates using 1.002 agar and not 1.040?
A: A number of reasons:
- Historically, beer-wort agar has had a gravity of 1.002 to 1.006. Presumably there is a good reason for this.
- 1.002 is more than sufficient too support yeast growth – don’t forget, yeast are drawing nutrients from around/underneath the colony, so in effect the entire thickness of the gel is feeding the small amount of yeast growing on the surface.
- At higher SG’s agar may not solidify properly, forming irregular or easily broken gels.
- Yeast on agar are exposed directly to air, which is dehydrating and puts a lot of stress on the yeast. A high SG agar will also draw water from the yeasts, further increasing the osmotic pressure and stressing the yeast.