Yeast film on rye starter
My rye starter is frequently afflicted with a film of yeast on top of it and I'm not sure why:
It looks like I'm not the only baker who seems to have this problem - look here:
https://www.thefreshloaf.com/node/24477/what-happened-my-starter-help
But I'm not sure why it is a recurring problem for me. Different rye flours - light and wholegrain and different starters, same problem. My wheat starter is fine.
My refreshment regime is 4g starter/12g rye flour/15g spring water at 28c for about 6 hours. The starter is then well risen and tastes acidic. I store it in the fridge and refresh weekly. But if I am much over a week, then often I can see (and smell) the yeast film. Interestingly, in this case, the acid seems to get "sucked out" of the starter and the pH goes up.
I seldom get any hooch on the rye starter, but if I do then the problem doesn't occur.
At the moment I'm playing around with refreshing for longer and at 32C, to get the pH right down, which hopefully will get the pH lower and stop the yeast film from growing. This is a bit inconvenient, however.
Any ideas?
Lance
Only 2 things come to minds
Either or a combination of the 2 - both can cause this. But ... you are trying to get a lower ph. Oh well! Enjoy!
Lance:
This is puzzling and worrisome and, honestly, I don't have any informed advice. But I wonder:
1. from your description of a 1:3:4 feed, am I correct that that means you're keeping your starter at 130% hydration. Might that have a bearing on the excess yeast formation.
2. Is the excess yeast growth simply a film? That is, is it possible to skim it off? What happens if you do? Does it grow again immediately?
3. Perhaps sprinkling a layer of dry rye flour on top of the starter, either just after you have fed it or just before stowing it in the fridge might stop the yeast skin from forming?
Rob
Well, from what I read, this kind of film is not toxic (kahm yeast?), so that's a good thing.
I can certainly scrape the film off and use some of the underneath stuff to make a good levain.
I have tried running at 100% hydration - that's when the problem first occured. I thought I would try 125% to see if that increased lactics to yeast balance.
At this moment I am going the other way and doing a refresh at 70% hydration. Let's see what happens. Your idea of sprinkling on flour might be a good one to try too. The other option I tried once or twice but without really following it up was to refresh at 125% and then stir in some fresh flour just before fridgeing. This is more work though; as we know, rye mixes are a good substitute for cement mortar.
Lance
I'm sure you've thoroughly researched this and know more than me, but, apparently, kahm yeast requires oxygen to grow. That's why I thought of putting a layer of flour on top of the starter. Another strategy might be to keep more starter or use a smaller jar -- the idea being to allow less air in the jar so there's less oxygen to feed the kahm yeast -- and possibly getting a new gasket to ensure your seal is secure. Finally, salt is apparently often used in various ferments to control kahm yeast--though I'd be wary of layering the top of a starter with salt because I'd fear that it would spread through the entire thing and retard all yeast development.
see: https://www.reddit.com/r/fermentation/comments/ytg2vy/kahm_down/?utm_source=share&utm_medium=web2x&context=3
Rob
I stopped using only rye for my stored starter. I just take out 30g when I am ready to use it and keep the storage as Arrowhead mills white + whatever there is left over from the one made for the bread I am making. So it is really a blend. ( process described below for clarity)
I also start a new sterilized jar every time I bake. I am keeping way less starter than I used to. I take out 30 g to feed up for the loaves I am making. I make 30 g extra and put that plus what was in the old jar over into a new jar that has been cleaned and rinsed out with a dilute bleach solution. All together there is always about 120g of starter .
I never feed what's stored I just put the fresh on top of what is stored and then when I am ready to bake I give it a good stir and take out 30g and repeat above process. This has stopped any growth of weird stuff on top as well as giving me a really healthy bubbly stored starter without ever leaving it out to room air/temperatures.
I think that was my problem . I also only feed the one time for what I need for a bake ex: usually need 250g of levain so I take out 30g and feed 140g flour and 140g water to get 280g bubbly starter and return 30g to stored clean jar. Hope this offers another option for you. c
Today's refresh 4/16/11 - 70% hydration, 28C, about 7 hours:
Nice and gassy and tastes acidic. I could check the pH, but it's such a pain getting the rye paste off the pH probe.
In the classic research tradition of changing two things at once, I also sprinkled some rye flour on top, following Rob's idea:
I'll see how it is in 7 days.
Rob, regarding limiting oxygen supply, I think the problem is that the level in the jar could be quite high straight after refresh, but drop down in storage. These are simple plastic pots with just a snap on lid - no airtight seal.
But thinking about it, another option might be to rest a small circle of baking paper on the surface or even one of the wax discs you can get for jam making....
Caroline, you seem to have developed a great starter workflow scheme. It's just the purist in me that wanted a true rye starter - born on rye and fed on rye. My wheat starter is a little complicated, having a bit of salt in it and 50% hydration, so I was hoping for the rye starter to be low maintenance. Oh well!
Lance
I had a rye to start with over 10 yrs ago...can't remember exactly when I started sourdough. Then I had a white one too. Then I made a yeast water and then I fed it with flour and made another stored starter. Then I got mad one day because I couldn't remember what was what. I decided who the hell cared ??!! So there was born the mixed heritage stored starter. I have no idea what's in it . Haven't worried in a lot of years. It raises great bread flawlessly. That's all I care about anymore.
I am glad you have started a solution that will hopefully stand you in good stead. I tried to post my porridge bread but I just can't get the photo thing on this site to work and the free photo edit programs are beyond me. So I will eat the bread and enjoy and look at everyone else's pictures :) c
Increase the feeding frequency, especially if the starter has been in the fridge for over a week. Another way is to add a bit of ripe starter during feeding, which helps maintain the balance between lactic acid bacteria and yeast.
Not harmful but normally a sign of under feeding. Yeasts go a bit 'rogue' (for want of a better term) and normally bounce back when given some TLC.
I agree, that looks like what we describe as 'kahm' yeast, which as you go down the rabbit hole turns into a very broad and vague term on the internet! Some people do say you get off tastes and flavours, but if everyone is referring to the same furry fungal culture remains a point of debate.
I struggled to uncontaminate my kefir culture that was infected with kahm, and eventually reverted to an untainted 'backup'.
Whilst you could revert back to backups on an ongoing basis, it doesn't prevent recurrence. Funny that the pH goes up, if there was some way to keep the pH down that would be first prize.
In a similar vein to reducing the hydration, I'm a great fan of 'semi-dehydrating' starter by rubbing it into small clumps in flour before storing the clumps (or the buried stater) in the fridge (or in a square of cheesecloth just on your desk if you're Jeffrey Hamelman). For fridge storage I add a desiccant pouch to the jar to prevent condensation.
In other words, a lot less than 70% hydration! It revives very well and fast if fresh (say a week or two) and still revives even after a year plus. So, a bit of backup and a bit of low hydration all rolled into one, and couldn't hurt as an offshoot of your regular starter jar.
Finally, there may be some merit to not going 6 hours before the fridge, maybe 2 hours, like the Jeffrey Hamelman link above?