So you open the lid to your bucket or peer through the glass of your carboy and what do you find, some gnarly looking whitish film, crust, or even little island floating on the surface. What is it? It has a variety of names such as film yeast, yeast rafts, flor, and pellicle. Is it harmful? Does it mean your cider is spoiled? How did it happen?
First, there is a difference between yeast and mold. I covered this in details in my post on mold. Mold is generally colorful while yeast is white or tannish. Film yeast, yeast rafts, flor, and pellicle are formed by yeast and not mold. In fact you might have noted in a previous Mālus Trvium that there is a gene in yeast that can promote the creation of flor, or flower in French or Portuguese. Besides the impact from the yeast that is present, there are also environmental aspects that help form a flor. These include temperature, humidity, pH, alcohol, and sulfur dioxide (SO2). However, the one thing that always has to be present is oxygen. Without oxygen, film yeast, flor, pellicle, or whatever you want to call it won’t form.
Is it harmful? No. Does it mean your hard cider is ruined? No. Is it desirable? Maybe. This is actually your cider protecting itself. This film or flor creates a barrier that limits the additional exposure of your cider to oxygen. It’s also a method used in the production of certain wines. For example, sherry is made by aging wine in oak barrels that are partially filled and have a loose bung in the barrel. The goal is to create a flor and let that evolve the flavor profile of the wine. So does a film on your cider mean it’s spoiled? Definitely not. It does mean it will taste differently. If you are trying to make a sherry-styled cider, it may be perfect. Ultimately, if you don’t want film yeast as part of your hard cider process, avoid oxygen.
Don’t miss any future Mālus Trivium articles. Follow me and you will get a link to my latest article delivered to your inbox. It’s that easy!
PricklyCider.com 
Film yeast is an infection that accelerates the oxidation of cider. It does the opposite of “protect”…rather, it’s a sign of spoilage.
Caught early its not a big deal. Sulfite, top up, and package sooner rather than later to eliminate oxygen exposure.
From Andew Leas website “Film yeasts (generally of the genera Candida, Pichia or Hansenula) will readily contaminate a slow and unsulphited fermentation, or a stored cider where the air has been allowed to get in. The organisms are present on the fruit and thrive in aerobic conditions, so they sometimes appear on the top of the liquid where they will start to break down the alcohol. Their presence is often detected by a strong smell of ethyl and amyl acetates, reminiscent of the solvents used in nail-varnish remover. In small amounts these compounds are important contributors to the overall flavour of cider but as soon as they become obvious then you have a problem. Sometimes more unpleasant musty or oxidised flavours are formed instead. The yeasts themselves form a greasy/powdery film on the surface of the cider, breaking up into small white sheets and dropping to the bottom of the vessel when disturbed. Prevention is better than cure but, if film yeasts take a hold, keep the vessel well topped-up to exclude air and add 100 ppm SO2 to keep the organisms in check. The cider may still be usable if infection has not gone too far but extra care must be taken during handling to make the conditions for their growth as unfavourable as possible. Vessels where infection has occurred should of course be properly sterilised before re-use.”
LikeLike
Thank you for your comments and input. The research I have done indicates that most film yeasts are a form of Saccharomyces versus non-Saccharomyces. They are also tolerant of sulfites. Sulfites are really only effective in preventing lactic acid bacteria, which I believe are beneficial to cider and not harmful. Treating with sulfites is not an effective prevention. Elimination of the oxygen is your best prevention.
As for creating a protective barrier, the film yeast can form a protective barrier. It will depend on the nature of the oxygen exposure. If it comes from a barrel where the oxygen enters through the wood, the film won’t protect it. If it is in stainless or glass and comes from the headspace, the film can create a protective layer. I suggest reviewing some of the research on Flor yeast. If you search the site for film yeast, I should have various articles that Include research papers you can reference.
I hope that helps.
LikeLike
I don’t think that is correct but I’m keen to see your sources.
Film-forming yeast consume oxygen and catalyze the oxidation of ethanol among other things. To regard this as “protection” I think is backwards.
As for sulfiting, it is effective against most non-sacch yeast…which film yeasts will almost always be.
See here a peer reviewed article which reccomends sulfite as a treatment for film yeast contamination. The species which usually make up pellicls are also enumerated. Additionally ,Sacch species can be “recovered” from pellicles which is not surprising.
“The denomination “film-forming yeasts” includes a group of species able to grow on the surface of wine, developing pellicles. Species of the genus Candida and Pichia are regarded as typical film-forming yeasts although S. cerevisiae, D. bruxellensis or Zygosaccharomyces bailii may also be recovered from wine pellicles ”
https://annalsmicrobiology.biomedcentral.com/articles/10.1007/s13213-010-0098-0
LikeLike
I think our difference of perspective might be resolved by acknowledging that “flor yeast” and “film yeast” refer to groups of organisms in winemaking.
LikeLike
*distinct* goups I should have said.
“Flor”, “film yeast” and “wine yeast” are three distinct groups (not necessarily clades).
From what I’ve read flor comprises 4 distinct species of S cerevisiea (beticus, cheresiensis, rouxii, and montuliensis). The usual pitched S. cerevisiae will not form a film spontaneousy in wine exposed to oxygen. The wine must be inoculated with the specific flor-forming strains.
LikeLike
Thank you so much for the explanation. I am so tickled that my 5 gallons of cider are ok. Many Blessings!
`Pearl
LikeLiked by 1 person
I have the white film on my pear cider in a gallon jug. How do I get it out from under the yeast?
LikeLike
Siphoning is the best method either with an auto siphon, which will allow you an easier way to start the process or just a tube where you need to suck the cider to get it started. I would plan to bottle it immediately with some sugar to avoid getting the film again.
LikeLike
Thank you for your reply. How does sugar deter the growth? How much should I add per gallon? I ended up siphoning and running it through coffee filters. More for my peace of mind than anything else.
LikeLike
Film yeast requires oxygen. That can be from dissolved oxygen or oxygen exposed through the headspace. Dissolved oxygen is added when you do things like siphoning, pouring, or doing things to your cider. They best way to remove this oxygen is to restart fermentation. Adding a little sugar (2.6 grams per liter) will create about 0.6 liters of CO2 per liter of cider. The yeast will process the available oxygen, release some CO2, which will fill your headspace. This means the film yeast can’t work. Bottling and carbonating with sugar does the same thing. Coffee filters would add a lot of dissolved oxygen and generally won’t filter out anything in the cider as they are too coarse.
LikeLike