Collecting wild yeast

[z-bob]

If I want to try to culture some wild yeast, collected from local berries, would it be better to use hopped wort initially, or apple juice? I want something that will favor the yeast and maybe even inhibit the bacteria. Not sure if I will ultimately use this yeast for beer, cider, or wine. (perhaps all 3)

 

[bucketnative]

Most would recommend a lightly hopped wort (<10 IBU) at about 1.02 for this purpose. Just enough to keep the wild things (bacteria) at bay. That still doesn't mean you won't have any contamination, it just lessens the chances.

 

[RPh_Guy]

I suggest 1.035-1.040 wort, pre-acidified to pH 4.0-4.5.

Only add hops if you want to inhibit lactic acid bacteria. Use at least 10 g/L for full inhibition.

Even if your culture doesn't appropriately ferment the wort (it probably won't), you can still use the culture for wine/cider.

 

[Vale71]

I'd add hops anyway as it inhibits any gram-positive critters and not just lactos. Who knows what else is lurking on those berries.

Even so you will be culturing a lot of stuff that might or might not be wild yeast. If you're really only interested in isolating a wild yeast strain this is a lot more complicated than just making a starter.

I would definitely not use apple juice as that would only spoil and you won't want to use it as a starter.

 

[RPh_Guy]

I'd add hops anyway as it inhibits any gram-positive critters and not just lactos. Who knows what else is lurking on those berries.

What in particular worries you?
Pre-acidification eliminates risk of Clostridium growth. Other pathogens are gram negative but they would die with the combination of alcohol and acidity.
Lots of delicious wine and beers are made with wild cultures.

Mold is the only thing to worry about, which is easily visible.

Even so you will be culturing a lot of stuff that might or might not be wild yeast. If you're really only interested in isolating a wild yeast strain this is a lot more complicated than just making a starter.

There will be yeast and bacteria. It's not that scary.

A wild culture will fully attenuate wine. The main considerations would be temperature control and whether you'd allow MLF.
For beer, if bottling you just need to give it an appropriate amount of time to reach a stable FG (months), but as I said it likely won't appropriately attenuate a beer. Most of my wild cultures have only around 50% attenuation, so I assume they don't ferment maltotriose. Some do, so maybe you'll get lucky.

Isolation isn't super complicated either. Wipe a bit of the wild culture onto an agar plate and then pick off a nice round dot to grow.

I would definitely not use apple juice as that would only spoil and you won't want to use it as a starter.

"Spoil" as in ferment? Yep, and once it ferments it will be a starter.

Cheers

 

[z-bob]

I made some starter wort yesterday -- 80 grams of DME in 800 ml of bottled water, and a few Nugget hops pellets. Boiled it for half an hour with a lid on the flask, topped it up with more bottled water to get 800 ml again and brought it just back to a boil, then turned it off. Today I decanted a few ounces into a sanitized half-pint fruit jar and added a pinch of citric acid and 2 dozen ripe buckthorn berries from my backyard. (yes I know they are somewhat poisonous. I also know it's an invasive species; I will cut it down and poison the stump in the spring now that it's big enough to make berries and I can identify it) I put a plastic canning jar lid on the jar but left it just a little loose so CO2 can escape.

Don't really know what I will do with the yeast, I mostly just wanna see if I can catch something from my back yard. I should know something in a few days

I will use the rest of the wort to make a starter from some yeast slurry in the fridge.

 

[monkeymath]

. Other pathogens are gram negative but they would die with the combination of alcohol and acidity.

As much as I love wild fermentations - just got home from a trip to Belgium where I visited a couple of traditional producers of Lambic; thoroughly amazed -, I feel like this might be missing an important detail:

Yes, once the pH drops below a certain level (iirc somewhere around 4.5?) and the alcohol reaches a certain level (I think around 2%?), pathogenic critters will be inhibited in their activity or even killed. But, depending on the amount of time it takes to get there, they might already have produced pathogenic substances which remain. Perhaps these quantities are negligible if it's merely a starter, where these substances will be diluted further, but still I think this is something to keep in mind or discuss.

 

[RPh_Guy]

Let's discuss!

Clostridium species can produce exotoxins.

4 things inhibit Clostridium in wort/beer:

1. Low pH (<4.5 completely inhibits)
2. Oxygen (even slight amounts)
3. Hops
4. Ethanol

Clostridium won't be present in any great quantity, since it's strictly anaerobic and only spreads through spores, mainly present in soil.

In unhopped wort:
Both yeast and lactic acid bacteria rapidly lower the pH. Oxygen is the key factor that prevents Clostridium growth before the microbes can take the wort/beer below the pH threshold.
Now you understand Clostridium's window for growth is negligible.

Furthermore, your body is perfectly capable of metabolizing trace amounts of toxin. Exotoxin from Clostridium botulinum is even used clinically (BOTOX®).

Also worth mentioning, Clostridium would generally produce some pretty nasty fecal aromas if it were growing, which would cause most of us to dump that particular batch.

What might be concerning?
Mold growth is problematic because it's allergenic and can produce toxins/carcinogens, however it's easy to identify by surface growth. Mold requires lots of oxygen, so once yeast fermentation begins, mold growth is no longer a possibility, assuming you use basic techniques to prevent oxidation.
There's also a theoretical possibility that enteric bacteria (coming from a fecal contamination) could survive (but not grow) in beer for a couple of days to weeks. A number of things would need to go wrong for you to get sick: fecal contamination of your beer (variable likelihood), a strain would need to be pathogenic (very unlikely), you'd need to consume it by tasting the beer before it dies (unlikely, unless you decide you want to drink the whole batch after a couple days of fermentation), and it would need to survive your stomach (maybe if you're on an acid-suppressing medication).

Lastly, there's never been a reported case of microbial-related food poisoning from beer.

Cheers

EDIT
Forgot Staph.
Staphylococcus can produce exotoxins.

Staph is very sensitive to both pH (<5.1) and ethanol (0.1% ABV or less), so it's inhibited even at normal post-boil wort pH (typically 5.0-5.2).
It's gram positive, so hops inhibit it as well.

I suggest 1.035-1.040 wort, pre-acidified to pH 4.0-4.5.

The procedure I recommend eliminates any risk to your health.
Fruit juice is also generally under low enough pH to prevent toxins.

 

[z-bob]

I think I caught something. The wort looks slightly fizzy, and the berries are floating. I'm not going to open the lid (and smell it) for a few days because I don't want any more oxygen to get in yet.

 

[monkeymath]

Let's discuss!

I'm glad you picked it up! Thanks for the info provided.
Do you have a reference for the details underpinning your statements? For example, you say that "even slight amounts" of oxygen inhibit clostridium: how much? And how much oxygen is dissolved in apple juice/starter wort?
Also, yeasts consume oxygen rather quickly (good for clostridium), but lower the pH (bad for clostridium). Now, can it be guaranteed (I remind you, unnecessarily of course, that spontaneous fermentations might vary depending on the specific surrounding microflora) that we will, at all times, have at least one of our two shields - oxygen and acidity - up to defend?

Just to be clear: I'm not saying your statements are incorrect, I just don't think they are true a priori, and I do not possess the necessary information to decide it.

Also, while I do understand that trace amounts of toxins cannot be fully avoided in a non-sterile environment (also not when we pitch commercial yeast), I'd still prefer to have a rather clear idea of the quantities we're talking about before declaring that it was a negligible quantity.

Again, thanks for your input, I'd be happy to hear more

 

[RPh_Guy]

This info is all based on scientific literature.

I ain't writing a formal paper here, so my statements should be enough to get you started to delve into the literature yourself if you want a deeper understanding. I'm just a random guy on the internet; you can believe me or not. (However I do have formal education in medical microbiology and toxicology.)
Google Scholar can help you access literature, often with full articles for free.

For example, you say that "even slight amounts" of oxygen inhibit clostridium: how much? And how much oxygen is dissolved in apple juice/starter wort?

Going by memory... A lab studied Clostridium growth in several tubes of growth media inoculated with Clostridium under varying levels of headspace oxygen, and incubated at an ideal temperature for Clostridium growth.
Growth in tubes with headspace oxygen concentration even lower than atmospheric concentration were inhibited.
A starter can be assumed to have 8ppm DO, which is at equilibrium with the atmospheric oxygen concentration in the headspace. This is more than enough to inhibit Clostridium, which is a strict anaerobe. Intolerance to oxygen is the definition of being a strict anaerobe (as opposed to facultative anaerobe, or aerobic).

Now, can it be guaranteed (I remind you, unnecessarily of course, that spontaneous fermentations might vary depending on the specific surrounding microflora) that we will, at all times, have at least one of our two shields - oxygen and acidity - up to defend?

Don't forget lactic acid bacteria also producing acid concomitantly with the yeast, that's a third shield. Our own ability to metabolize trace amounts of toxin and our noses to detect Clostridium growth are the forth and fifth shields, so yes, it guaranteed won't be a problem.

Remember these bacteria can only grow in unhopped wort. Just add hops to your wort starter or spontaneous fermentation if the thought bothers you. Easy Peasy. 1-2g/L hops will suffice, and many wild strains of LAB can overcome this hopping rate.

If you are spontaneously fermenting a batch, then hops (particularly aged hops) are definitely recommended because you want to delay souring for a few months so the yeast can produce flavor without being suppressed by acid.

I do understand that trace amounts of toxins cannot be fully avoided in a non-sterile environment (also not when we pitch commercial yeast), I'd still prefer to have a rather clear idea of the quantities we're talking about before declaring that it was a negligible quantity.

That's completely true. In fact, many toxins come from the grain itself (most grain is contaminated with trace mycotoxins), and yeast produce ethanol, which is absolutely a toxin. We are literally drinking poison.

You get a dose of carcinogens from just breathing the air around most plastics (e.g. that plastic smell like a new car), from breathing the air in a city, from filling up a tank of gas .... You could spend your entire life worrying about these things if you want. Or you can accept that it's not a major threat and move on to things that matter. It's about perspective.

 

[z-bob]

So what should I make first with it after I step it up? (not going to to a streak plate) A wheat beer, or a gallon of low-ABV (just juice and no sugar) cider? It looks pretty clean; still slowly fermenting with a nice little layer of bubbles on top and no mold. I'm thinking of cold-crashing it early just so I can remove the berries w/o losing much yeast, then add a little more wort and let it keep going.

 

[monkeymath]

So what should I make first with it after I step it up? (not going to to a streak plate) A wheat beer, or a gallon of low-ABV (just juice and no sugar) cider? It looks pretty clean; still slowly fermenting with a nice little layer of bubbles on top and no mold. I'm thinking of cold-crashing it early just so I can remove the berries w/o losing much yeast, then add a little more wort and let it keep going.

I wouldn't cold-crash it. Commercial yeast flocculates well because the flocculant yeasts have been selected for, but with the wild ones, you'd probably lose more than you gain.

(On an unrelated note, I also don't cold crash with commercial yeasts because the starter is there to make the yeast happy, and cold crashing does not make yeast happy at all.)

 

[bracconiere]

i'd say, look into sterile technique and use wort....Mason jars in a pressure cooker, but to actually get a clean strain, you're going to need something like this..

But on the other hand, if you just want mostly yeast, lol....just brew a few batches of beer with it, repitching the trub each time....

edit: and if you have something like my glove box...start by doing some agar petri dishes so you can transfer away from the contaminants for a few plates, then grow the yeast out...

(i hate to recommend it, their all drug addicts, but the www.shroomery.com might be a better resource for you)

 

[RPh_Guy]

You need to check the attenuation before you know if you can make beer from that culture.

 

[cmac62]

I'd say step it up to a gallon batch and then you can do OG-FG readings to get the attenuation. I would also do it relatively warm for the first batch, say in the 70-75 range.