Pellicle Quest

micro/macro pellicle

One word had escaped the etymology dragnet I’ve set up to write my Anglica Brewtannica series: Pellicle.  How had I missed pellicle?  It sure sounds kinda medieval.  Or like one of T.S. Eliot’s cats (Jellicles, Pollicles).   Come to think on it, I kinda know what one is regarding beer, but do I really-?  I better go check on that…

I’ve been writing a series of articles for Tournaments Illuminated on the etymologies of brewing words.  It struck me that most of the common words we use seem very old to my ear.  I wondered whether we’d borrowed them from other nations such as Germany.  It turns out most of them have been in English as long as there’s been English, and in some cases, a lot longer than that.  There are cognates for many of them all over Europe.  As near as I can tell, we humans have been brewing beer for, literally, longer than we can remember.  It’s given me a pretty thorough look at the words we use to talk about brewing.  So how did I miss this one?**

So let’s start with the dictionary.  A pellicle is a protective cover, a thin skin or membrane, or a liquid film – could be a thin layer supporting the cell membrane in various protozoa, or the thin layer of salivary glycoproteins deposited on the teeth of many species through normal biologic processes (the proverbial skin of your teeth).  It can be a thin plastic membrane used as a beam splitter in optical systems, which I think is way cool, but I hope has nothing to do with brewing. It’s closely related to pellitory, the name of an herb I had to track to New Zealand to make Aqua Composita and Aqua Rubea from Plat’s 1609 recipe several years ago.  It seems pellitory was once used for toothache and facial neuralgia, which goes back to the skin of your teeth example.

(I remember having a batch of beer that developed floating patches, and wondering worriedly whether they were spoilage.  I was able to rack them away, very very carefully, when the time came, and the beer tasted fine.  I remember the semi-solid patches, though, clinging to the sides of the carboy as I racked the beer out from underneath.)

Of course I went first to the Biohazard Lambic Brewers Page, figuring if they don’t about pellicles no one will.  There’s an excellent photo of the top of a carboy with year-old lambic.  The texture is almost corrugated, very brain-like, and is reported to be about 1.5 inches thick and composed of various wild yeasts.  Apparently, left to itself, this yeast culture could mat together and float; the yeast liked the oxygen available to it at the top of the wort.  OK, the patches on my beer looked nothing like this, but they never got more than a few months old.  I went back to look at higher magnification photos; just looked more like brain.  The author said it was composed of various wild yeasts, including brettanomyces and candida strains, not (emphasize not)  bacteria.  Apparently, lambics can reside en carboi for months or even years, and the pellicle that forms will wax and wane with the seasons.  They can sink and become part of the trub, then form again later…sounds like a fun school science project.

After reading these flights of high-stylin’ yeast management, I settled back down to good ol’ Homebrewtalk threads on pellicle.  What they describe still doesn’t sound like my batch with the floating patches.  Their pellicles were lumpy, slimy white film formed by some strains of wild yeast, particularly brettanomyces, during fermentation.  Apparently this almost always indicates infection.  If you really have a brett infection and you didn’t want to, you will have to clean your equipment particularly, and replace all the plastic bits; never let wooden implements touch infected wort unless you mean them to never touch anything else again.  Brettanomyces’ natural habitat is trees and lumber.

I went looking to find non-lambic brewing yeasts that  form pellicle naturally, as a normal part of their process.  I found more descriptions – “yeast islands” (that sounds like what I had) that grew until it covered the whole beer and formed a nice, solid, somewhat ropy layer (mine never did that).  MrBeer’s pictures sure looked like mine had, though, almost like congealed fat floating on the top of a pan, with a tendency to stick to the sides.  A number of commenters mentioned having similar things happen to their beer.  Commenters all agreed it wouldn’t hurt those who drank the beer – if it tasted ok, it was probably going to be ok – which is a little wishful when you’re talking about microorganisms, I mean, look at botulism.

A couple of commenters also mentioned that, in their carboys that developed unintended pellicle, they got a lot less trub, or yeast cake, at the bottom than they usually did with that recipe/yeast variety.  They all metaphorically shrugged and figured the yeast got tangled up in whatever process was going on on top.

Of course, it’s also possible that what I saw, at least at first, were little mini-krauesens, little isles of foaming fermenting goodness.  If so, they sure lingered for a while.

So I ask again: are there kinds of beer that do this as part of their natural fermentation cycle?  (I know, from the yeast’s point of view the cycle isn’t about fermentation.)  And, finally, I found a pretty clear answer in My Brothers Brew (Blogging Under the Influence…).  There were some nauseating pictures of various pellicles, let me tell you.  But he says: yeast of the saccharomyces genus do not form pellicles.  Brettanomyces does, and can ensnare other organisms in its net.  The only thing pellicle really shows is that there is oxygen in the fermenter.  Brett needs oxygen to grow, so when it’s exhausted the supply in the wort it comes to the surface to look for more.  It coincidentally minimizes further oxidation in the wort, protecting it from acetobacter (the stuff that makes vinegar) and the like.  Apparently pellicle can’t form inside a barrel – not enough to metabolize – but plastic fermenters allow more than 100 times more oxygen into the wort, so the pellicle tends to drop prematurely, giving your beer an unpleasant amount of sourness.  If you’re after a fine sour beer, don’t use plastic fermenters.

Oh, and pellicle doesn’t have to be present for you to get a sour beer, if that’s what you’re after.

Brettanomyces, lactobacillus, and pediococcus, while generally considered contaminants, are all added to some beers for specific effects.  I see another blog topic coming…

**To be fair, the earliest mention of a pellicle in writing is 1547 – well within the Brewtannica timeframe – but there are no references to it outside of anatomy well into the nineteenth century, so far as I know.  Which is weird, if you think on it, since Belgians were already making sour beers and there was a significant influx of Belgian/Netherlandish brewers to England in the fifteenth century.  They brought (hopped) beer in opposition to the local ale…maybe sour beer just didn’t make it into English palates and hearts for a while.


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