Yeast not growing??

[frankvw]

Hi, everyone,

I'm trying to propagate yeast. I made a medium-gravity wort (1045) from liquid malt extract, added 500ml (= two cups in Church of England measurements) of it to a lab flask, aerated it, pitched my yeast sample, and waited for things to happen. (Needless to say I have been anal about keeping everything as sterile as possible.)

The yeast pretty much started fermenting the wort immediately (judged by bubbles coming out of the airlock) and has now settled again. The volume of yeast at the bottom of the flask is exactly the same as I started with. The yeast looks healthy and there are no funny smells, but the volume of yeast has not increased.

I poured off the beer, added a fresh quantity of well-aerated wort, and exactly the same thing happened.

What could cause this? The only thing I can think of is lack of nutrients for the yeast to work with, but in theory the wort should contain enough nutrients. Could it be a lack of nitrogen in the LME-based wort? Any other possible reason?

All thoughts appreciated. Cheers!

// FvW

 

[william_shakes_beer]

How are you measuring the "amount of yeast in the bottom of the flask" ? Did you periodically shake it? stir plate? leave it alone? how did you control temps? how long did you cold crash?

Starter feremntation can go fairly quickly due to the small amount of wort involved. FYI I usually do 4 cups of water to 1 cup DME and put it on a stir plate. I place it on my kitchen countertop and turn on the under counter high intensity lights for a heat source. The termo on the countertop tells me i'm well within the ferm temp for the yeast. After krausen has fallen back I toss it into the frige to cold crash (flocculate the majority of the yeast to the bottom) and the pour off the starter beer.

 

[daksin]

If it fermented, you definitely have more yeast than you started with. 500mL is a small starter, though. You should use a calculator like mrmalty.com or yeastcalc.com to determine how much you need based on your volume of beer, gravity, and yeast age.

 

[frankvw]

How are you measuring the "amount of yeast in the bottom of the flask"?

I simply measured the thickness of the layer at the bottom. It does not increase.

Did you periodically shake it? stir plate? leave it alone? how did you control temps? how long did you cold crash?

I have shaken the flask twice a day. No stir plate. No temperature control (i.e. the wort is at room temperature). No cold crash; just normal flocculation at ambient temperature over the course of several days.

Starter feremntation can go fairly quickly due to the small amount of wort involved.

I know.

// FvW

 

[frankvw]

If it fermented, you definitely have more yeast than you started with. 500mL is a small starter, though. You should use a calculator like mrmalty.com or yeastcalc.com to determine how much you need based on your volume of beer, gravity, and yeast age.

Good point. I will try a larger volume, and add a little nitrogen (in the form of ammonium bicarbonate) too because I've been told by serveral people that wort made from LME might be a bit low in nitrogen. Let's see what happens!

// FvW

 

[william_shakes_beer]

Suggest you get a small thermometer designed to measure air tempderature and place it next to the starter vessle and see what "ambient temperature " is. You want to ensure your temp is within the range. I dont know about you, but I am frugal and tend to keep the house on the cold side during winter months.

 

[Huff360]

Ditch the airlock and replace it with a pie e of loosely wrapped foil. The point of the starter is to get as much oxygen in there as you can. The airlock defeats that purpose.

Once the yeast eat up all the oxygen in your well aerated wort, they go into fermentation mode. If you give them an infinite supply of oxygen they can reproduce as much as possible for the given amount of wort and not be limited by the available oxygen.

 

[frankvw]

I dont know about you, but I am frugal and tend to keep the house on the cold side during winter months.

I post from South Africa. It's late summer here.

 

[WoodlandBrew]

How much yeast, and where is it from? If you are approaching 300 million per ml you aren't going to see much growth. If the yeast is from a manufacture then the density is about 3-4 billion per ml, if it is from a starter made with DME then 2 billion per ml, if it is from an all grain fermentation then 1 billion per ml (or less)