Identifying wild yeast based on krausen/pellicle?

Until recently I'd never brewed with anything other than commercial Sacc strains, so I really have no idea what various yeast strains and bugs look like during various phases of fermentation. From what I gather, due to the blended nature of most lambic/sour brewing, it's difficult to determine which microbe is causing various qualities in the pellicle and whatnot. However, I figured it couldn't hurt to ask.

I posted a picture of this in the pellicle picture thread, but the point of that was to share, rather than seek input. I collected this yeast from dates, and I'm pretty sure it is a single species of yeast, since I streaked it on an agar plate and selected an isolated colony. However, I have no idea if it's Brett, Sacc, Zygosacc, etc., since I have no microscope or anything like that. I thought it might be Sacc at first, because it had a krausen that looked a lot like sacc, but now it's developing a pellicle (a little over a month in primary), so I'm wondering if maybe it's brett? The hydro sample I tasted about a week ago was definitely vaguely "earthy," but not overwhelmingly so, and not "funky" or "cherry pie" at all.

Here are pictures, first the krausen (a few days after pitching), then the pellicle forming (about a month after pitching):

In my (limited) experience with both sours and infections, it looks like at a minimum you have lactobacillus. Lacto tends to make those white specks, forms a bubbly pellicle and if given enough time may lay down a uniformly white layer across the surface.

ReverseApacheMaster said:

In my (limited) experience with both sours and infections, it looks like at a minimum you have lactobacillus. Lacto tends to make those white specks, forms a bubbly pellicle and if given enough time may lay down a uniformly white layer across the surface.

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That's interesting, since I really thought I was being careful with my sanitation and isolation process, and I even used sabouraud dextrose agar in an attempt to discourage bacterial growth. Obviously lacto infections can happen regardless of the source of the yeast, but it's kinda frustrating if that's the case here, since I was hoping to get a feel for this yeast's characteristics for use in future brews.

Question for microbiologist types: If I were to harvest a little of the pellicle and streak it on some regular agar plates, what would lactobacillus look like, as compared to yeast species? Does it have a recognizable growth pattern on agar?

This likes the pellicle on my lambics. I typically pitch sach, brett, lacto and pedio.

Even the same organism can form different looking pellicles each time, so it's hard to say.

To me that doesnt really look strange, it looks like some bubbles and trub/protein on the top, especially if it doesnt taste sour I would say that its not infected

What was your recipe?

ryane said:

To me that doesnt really look strange, it looks like some bubbles and trub/protein on the top, especially if it doesnt taste sour I would say that its not infected

What was your recipe?

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It was basically just DME (my first extract batch in years, been doing all-grain for awhile now), plus a little bit of hops, with the purpose of seeing what this wild yeast strain was like. As stated above, I had isolated the yeast from some dates by streaking it on agar, so I was hoping it was a single organism.

The beer had completely cleared and the surface was smooth, with just a few bits of trub/hop particles, and then about a week ago the white flecks started appearing and those bigger bubbles started forming, so it really does look more like a pellicle than just protein/trub, though I've never seen one form before.

winnph said:

That's interesting, since I really thought I was being careful with my sanitation and isolation process, and I even used sabouraud dextrose agar in an attempt to discourage bacterial growth. Obviously lacto infections can happen regardless of the source of the yeast, but it's kinda frustrating if that's the case here, since I was hoping to get a feel for this yeast's characteristics for use in future brews.

Question for microbiologist types: If I were to harvest a little of the pellicle and streak it on some regular agar plates, what would lactobacillus look like, as compared to yeast species? Does it have a recognizable growth pattern on agar?

Click to expand...

If you streak a plate and there's lactobacillus in the culture then the colonies will be very small. Lactobacillus is microaerobic and you actually need an anaerobic growth chamber to grow normal sized colonies for pure culturing techniques. Another way to rule out the lactobacillus is to use a pH differential media. If you streak the plate and the media is blue (as in wallerstein differential) and the plate turns green (due to acid production) with real small colonies, chances are it's lactobacillus.

Does the beer taste sour? If it doesn't I doubt you have a lactobacillus problem when you used pure culturing techniques to isolate a colony from the dates. You just have a strange looking pellicle is my guess.

smokinghole said:

If you streak a plate and there's lactobacillus in the culture then the colonies will be very small. Lactobacillus is microaerobic and you actually need an anaerobic growth chamber to grow normal sized colonies for pure culturing techniques. Another way to rule out the lactobacillus is to use a pH differential media. If you streak the plate and the media is blue (as in wallerstein differential) and the plate turns green (due to acid production) with real small colonies, chances are it's lactobacillus.

Does the beer taste sour? If it doesn't I doubt you have a lactobacillus problem when you used pure culturing techniques to isolate a colony from the dates. You just have a strange looking pellicle is my guess.

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Thanks for all that information! I don't have any pH differential media, so I'll just have to taste it when I pull my next hydrometer sample (planned for end of this week). The last sample, around March 21, was not sour, but the pellicle had not really taken shape yet. I'd noticed the white flecks forming on the surface when I pulled the sample, but it wasn't until about a week later that it really started creating the film and the bubbles started growing. I figured it must have been triggered by the introduction of oxygen when I removed the airlock for the first time since fermentation had begun, but I guess I could have introduced a bug of some sort.

Do you have any kind of pH indicator solution? If you do you can check the beer at different stages to see if it changes pH over time. That will also give an indication of either lactobacillus or pediococcus. Other thing to note. Though it's small and strain dependent brettanomyces can also produce acetic acid like pediococcus just that brett does it in much smaller quantities.

I just took a sample -- SG hasn't budged in the last 17 days or so, so I'm gonna go ahead and call this the FG. Went from 1.045 to 1.011, which is about 75% apparent attenuation.

Flavor is definitely not sour at all, mostly just clean, crisp and with the ever so slightest hint of funk/tartness, but I might even be imagining it. Really an amazingly clean, tasty yeast, and I'm definitely going to save this slurry for a larger late-summer batch when I bottle this one over the weekend.

More info for anyone who's interested: Wild Ale I recipe (Wild Ale I brewer's log)

I forgot to take a picture when I just drank this sample, but it looked exactly like the one I took 17 days ago: