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althalos 06-01-2009 01:43 PM

Solvent/Fusel Alcohol Flavor Using Homegrown Yeast
I am a yeast researcher, so I store my brewing yeast long term in -80C. When I get ready to make my starter, I take a swipe of yeast and plate it on a YEPD plate, which is comprised of yeast extract peptone, peptone, and dextrose (essentially dead yeast components, proteins, and corn sugar). This is standard in the lab. Once the yeast has grown up at room temperature on the plate, I take a colony to make a starter out of it using DME and a little fermaid-k. All the beers I have done this with have had an odd solvent/fusel alcohol taste to them. I use a counterflow chiller and do not separate the cold/hot breaks before going into the fermenter (I just stick the cold wort exit tube into the sanitized fermenter). I am confident that my sanitization, brewing temperatures, time at which I transfer to secondary, etc. are all on point.

I think the flavors could be a result of the plate I was growing them on, because one time I made the starter in a similar way (yeast extract, peptone, and maltose), and centrifuged the yeast to pitch, and the solvent flavor was so bad I had to scrap the entire batch.

However, the flavor could also be a result of not separating the trub after counterflow chilling, i.e., putting it into a separate container, letting the trub settle, and siphoning off the top.

Or it could be a combination of the two.

Does anyone have any recommendations? I think next time it would be a good idea to plate on a DME/agar plate, and transfer to a DME liquid culture, and separate the trub after fermenting.

Any help is greatly appreciated.

scinerd3000 06-01-2009 05:12 PM

are you replating the yeast cultures? The only thing i can think of is that they possibly sat too long. Also look into plating on malt agar- i have heard (jamile) for example that if your making a cider and create a starter in apple juice, the yeast will not then be able to ferment maltose. I could be mistaken but wouldnt this carry over to how the yeast are plated considering there is no malt extract in the origional growth medium?

ColoradoXJ13 06-01-2009 06:53 PM

I did the same things when I used to work in an academic lab, can't do it anymore in priovate sector. I never had problems with the techniques you described and off flavors. I would personally skip the plating, some yeast strains are actually mixed (some witbier cultures have multiple strain) and by isolating a single colony, you run this risk of picking the wrong one, or a mutant of some sort.

What are your fermentation temperatures? I find that hot fermentation results in the flavors you describe...do they correlate with summer coming on?

FlyGuy 06-02-2009 12:30 PM

Fusel/solvent off-flavours sounds like a fermentation problem (e.g., fermenting too warm) rather than a yeast culturing problem. Higher alcohols are produced by stressed yeast.

dinertime 06-03-2009 07:54 PM

I too work in a yeast lab (though I am pretty new to this field of biology) and would second ColoradoXJ13 in that it might be better to put a whole swab of cells directly into a liquid culture than to take just a single colony.

Also I would try re-diluting the starter culture once or twice into fresh DME before pitching, as maybe the cells need some more time to acclimate to the new media.

TheChemist 06-03-2009 08:08 PM

I learnt to use malt agar, like scinerd mentioned. We put malt agar in small sterile universal bottles, and tilted them so they solidified at an angle. You can spread a colony on the surface of the agar, culture it, and have a 'yeast slope'. Then, you rinse the tube with some sterile wort and culture it up in a small batch (500ml or so), and then pitch the cultured wort.

When you say you plate it, do you mean using WLN agar plates? I haven't heard of issues with that creating fusel alcohol production before.... Like Colorado and FlyGuy mentioned, that problem is a lot more familiar to me with high fermentation temps.

althalos 06-05-2009 04:19 PM

Thanks for all the replies.

My fermentation temperatures are always around 68F (I only have the capacity to brew ales right now).

I have also heard from my homebrew store owner that the yeast have a difficult time acclimating to the new "wort" environment after being on a substrate that does not contain maltose, the primary sugar in wort. They are not as good as yeast grown in wort at fermenting out to the described attentuation.

To clarify, the plates in the lab we use are YEPD plates, which contain yeast extract (dead yeast cells in powder form), peptone (a mix of proteins), and dextrose (corn sugar).

It probably should have occurred to me that if I was going to use these cells to make beer, then they should be cultured on media similar to wort. From now on, my yeast will be grown on hopped malt agar with yeast nutrient on slants.

By the way, I have been looking at some commercial solid media called UBA - universal beer agar. Has anyone used this, or does anyone have any thoughts?


Bendbiker 06-12-2009 06:59 PM

I also work in a lab and do something similar. I usually grow a 2ml starter from my -80C glycerol stock in YPD media then transfer to 500ml the next day and grow a second overnight. After that I resuspend the yeasties in phosphate buffered saline, smuggle home the yeasties in a tube, and use the suspension to make a starter in 1500ml of DME wort the same night. They seem to have no problem taking off/ making the transition.

I don't normally work with yeast in the lab, but many of my colleagues do. I decided I wouldn't pitch anything with YPD in it, because the yeast extract smells AWFUL. Since taste is usually parts per million, I didn't want this retched smelling (and probably tasting) stuff in my beer.

This strategy has worked well for me. Even though I'm leaving my lab now, my colleagues are letting me keep my -80C library of yeasts and come in to grow them up when I like in exchange for a beer every now and again. Great deal for me. $12 a tube for white labs is a bit o cash!

althalos 06-26-2009 07:35 PM

That's interesting, Bendbiker. I can't remember if I washed them last time; I'm pretty sure I did, and I didn't wash the batch before that, and the taste was so awful I had to throw the beer away. Maybe there was a little residual YPD liquid in there. Regardless, growing them on malt agar should circumvent the entire problem. My guy at the beer store recommended at least two generations on malt agar before transferring to starter, to give the yeast plenty of time to readjust to using wort as a carbon source.

iamatuna 03-27-2011 05:22 PM


Im a student in microbiology and ive worked with yeast a bunch and done some of the same things. I have used UBA - universal beer agar for a few lab samples which we as a lab then used to make beer and it turned out alright but we were also making 20G batches so if there was any sort of residual media taste it was diluted much more so (We made a starter with DME).

For all of my home brewing i have always used dead yeast (i just throw the culture in the microwave for about 10 mins to kill them all) add some DME and then add gelatin; I dont have access to agar at home. All of my results have worked fine.

In terms of the generation times on different media i think there is deffinatly something to it. I have made a few batches of cider where i have used the same yeast strain (WLP300) one straight from the bottle, one from a hefe batch and the other from a starter made in apple juice each have a dramatically different taste.

Hope that helps, lol might revive an old thread.


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