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That sounds like acetaldehyde. The level could be higher than normal due to a high fermentation temperature. The good news is that it should mellow with age. http://www.howtobrew.com/section4/chapter21-2.html

All of the yeast that has settled at the bottom is fine to use. Microscope analysis has showed that there is very little difference in viability and protein trub between the layers. See here for details: http://www.woodlandbrew.com/2012/12/yeast-washing-exposed.html...

Thanks! I hope it works for you, but I suspect it may take some tweaking. I'd be very interested to hear how it works for you.

Thanks for the kind words @bietourist. Your support is appreciated. @eadavis80 Good luck on your brew!

If it were me I would just save enough slurry in a mason jar for the next batch. I like to keep it simple. Not only because it's easy, but because it reduces the chance of contamination.

Foam is proportional to CO2 production rate which is proportional to metabolic rate which is proportional to cell density and gravity. For a picture of what is going on try this Starter Calculator: http://www.woodlandbrew.com/2015/02/starter-calculator.html

That's been one of of my pet peeves as well which is why I implemented it in my starter calculator. From the graph you can see that if you start a two liter starter tonight then by Sunday night you should have about 200 billion cells on the low end. Because the yeast has been refrigerated...

A 2 liter starter without a stir plate should yield about 270 billion cells after 3.5 days. There is also statistical analysis to my calculator to show typical variation. The low side is 220 billion and the high side is 290 billion.

I've been doing some work with microscopy and viability and wanted to share what I have learned. Whether or not you are familiar with ImageJ or automated image analysis you might find this interesting. http://www.woodlandbrew.com/2015/02/automated-cell-counting-of-yeast-using.html

Try this calculator: http://www.woodlandbrew.com/2015/02/starter-calculator.html The short answer is: no, you don't need a 5 liter starter. A stirred starters produce cells faster, but given enough time a starter with only aeration at inoculation will produce nearly the same cell count...

A 158° Mash temperature will also contribute to less fermentable sugars. Here are some things you might consider to lower your gravity: http://www.woodlandbrew.com/2012/11/top-ten-ways-to-restart-fermentation.html http://www.woodlandbrew.com/2012/11/top-ten-reasons-why-your-final-gravity.html

Here are more details on swap coolers including thermal coefficients: http://www.woodlandbrew.com/2012/09/swamp-cooler.html There is a product that looks like a cylindrical insulated pizza bag that I have not tried myself, but have heard good thing about. https://www.cool-brewing.com/

Biomass yield is directly proportional to extract for the most part. For a quick estimate each gram of extract will produce about 1 billion cells. Here's my calculator that shows growth over time: http://www.woodlandbrew.com/2015/02/starter-calculator.html The typical starter will yield...

Even if it drops out completely clear you'll get enough yeast off the bottom when you rack to the bottling bucket. Viability might be a little low if the ABV level is high and it has been sitting on the cake for a while. See here for details...

That's a novel solution to a problem. Very clever. I'm curious as to how it comes out. During the initial phase yeast are adapting to their environment and adapting their environment to suit their needs. I would be a little concerned that the environment is a moving target as the temperature...

Well, I got automated cell counts working pretty well with ImageJ. Here are the details including macros: http://www.woodlandbrew.com/2015/02/automated-cell-counting-of-yeast-using.html

Use of glycogen to synthetises sterols is prefered by the yeast, but absence of glycogen does not mean that sterols are not synthesized. If there is no stored glycogen then the yeast will created it from wort constitutes. This occurs much slower with poor cell permeability, but eventually the...

In my experience, low glycogen content (low vitality) leads to a longer lag time, but does not impact the yeasts ability to ferment. My understanding is that the lag time is longer because the yeast do not have glycogen to aid in sterol production. However once the yeast have prepared their...

Brewers Friend has a procedure and spreadsheet for that: http://www.brewersfriend.com/how-to-determine-your-refractometers-wort-correction-factor/

Nice write up on different types of thermometers. Maybe it depends on which bargain IR thermometer you have, but the one I got from Harbor Freight has a 0.5F resolution and the accuracy is about 1F when measuring boiling water. There is both an offset and gain error associated with any...