16

Speaking from experience as a molecular biologist. Erlenmeyer flasks are nice for a couple of reasons. The main alternative being a standard beaker which is essentially the same size at the top and the bottom. First off the neck size makes it easy to hold in the hand. Second a smaller opening reduces the chance of getting airborne material into the flask. ...


11

Stirring is not needed while the yeast are actively fermenting because the fermenting wort is naturally turbulent - i.e. it self-stirs. This churning mixes the wort ensuring the yeast are suspended more-or-less throughout the wort, so they are always in contact with their food supply, making additional stirring redundant. The turbulence in the wort comes ...


4

Smack packs contain yeast nutrients, and sugars nothing magical. Its just a mini starter in a bag for proofing yeast for direct pitching. Don't need it at all If doing your own starter. If you do all grain your wort has all the nutrients it needs. Sounds like your 1st stage went fine. I would just step up as normal. At the risk of infection just throw the ...


4

I use a 750 ml bottle, sanitised aluminium foil and a rubber band. Keep aerate by shaking it occasionally during the first 12h; I shake it every 6th hour or so. After 18-48h I use it or refrigerate it for later use. I use White Labs instructions for reference, no matter the brand of yeast I buy. Cheers!


4

Yes you can. I've fermented apple wine this way on a DIY stirplate, 1 inch magnet, and a vintage arrowhead carboy (flat bottom). It wasn't powerful enough to make a deep cone for oxygenating which actually worked nice as I just wanted to deny the yeast the option to flocculate. My stirplate uses an old SCSI external 5.25 tape drive, so it's platform is ...


3

I haven't noticed any difference in the performance of my home-built stir plate between water and wort/yeast with one exception. I often make two-stage starters and refrigerate the flask between stages. then decant most of the old wort and add new wort. The resultant yeast slurry is very thick, and the stir plate can't turn the bar through the thick slurry. ...


3

There are two key variables in a yeast starter - the volume of wort and the gravity of the wort. The volume principally determines how many cells you get out of the starter. The gravity also has some affect, but most texts recommend a gravity in the range 1.030-1.040. This is to avoid too high stresses on the yeast, and also because oxygen dissolves more ...


2

http://braukaiser.com/blog/blog/2013/03/25/stir-speed-and-yeast-growth/ and the first link it contains address these points exactly.


2

It matters a little bit. The advice I've seen is that a wort of around 1.040 is best for a yeast starter, presumably because that's the optimal level of fermentables for yeast propagation. 1/2 cup of DME in 500ml of water yields a gravity around 1.040. So the wort from 1 cup in 800ml will have a higher gravity -- somewhere around 1.065. The yeast will not ...


2

While starters ideally don't make use of an airlock to promote maximum O2 exchange, some people prefer to use an airlock to counter wild yeasts and other contaminants. The narrow neck on the conical flask makes using a stopper and an airlock much more practical. Alternatives to rubber stoppers are foam stoppers which permit gas exchange. Again, these would ...


2

Too much oxygen in a starter is almost impossible, so long as you decant the liquid and don't pitch it with the yeast. If you plan to pitch the liquid (e.g. to kraeusen a beer or restart a stuck ferment) then don't stir at all since you'll be pitching oxidized wort. A vortex isn't necessary for oxygen uptake - just having the surface in continual motion ...


2

'Is such a high growth rate (assuming that everything is optimal) actually possible[...]?' It sure is. Yeast will pretty much grow indefinitely as long as there are no nutrient limitations or inhibitory levels of ethanol. The major limiting nutrients are: Fermentable sugar Nitrogen (amino acids, basically) Oxygen (more accurately, the lipids synthesized in ...


2

You could build a stir plate - you probably already have most the stuff laying around. Step 1: Gather a computer fan, power supply, stir magnet, and neodymium magnets and 2 L mason jars. Step 2: Glue 2 neodymium magnets to the computer fan facing upward, with one + side up, the other - side up. The diameter should be the length of your stir magnet. Step 3:...


2

A stir plate does two things. Both can be done manually by swirling your vessel. Provides the yeast a good amount of oxygen. Reduces yeast lost, from lifting out with krausen and drying on the sides. Put your starter in a common place like in the kitchen and swirl of whenever you walk by. Erlenmeyer flasks are unique in that they are made of Pyrex and ...


1

I Use various size canning jars, I have the, from .5L up to Half Gallon. I only fill them up Half way to 3/4 full. And when making the starter, I leave the lid partially screwed on. Then during the process, every time i walk by Open up the jar swirl Then I spend about 10 seconds shaking it with the lid on Tight. then crack it.


1

I don't think you need something so heavy duty for the batch sizes you're talking about. The "standard" homebrew stir plates are generally built with hard-drive magnets and computer case fans. These can readily move wort in flasks from 2-4L, and probably up to 6L, as well, with just a bigger stir-bar. Looking at yeast-starter calculators, for 100L of low-...


1

Assuming you're talking about when the yeast is first pitched, we do shake the carboy. Or, well, I do, in order to get oxygen into the wort. As for a stirplate, I would imagine that it would have to be fairly big to scale up to carboy dimensions. And your stirbar would be sitting in the carboy until you were ready to transfer.


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