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It's because it's my first time harvesting yeast,, my thoughts was to use a beer make it flat add little bit of sugar and yeast to make sure it works before.
I found thus link below to build a stir plate, just got to find the time.
If you followed a tried & true practices, I assume you watched Scott's method, and its a real recent harvest and you are brewing real soon, I wouldn't bother trying to test it. Run with it. You'll be surprised...the good kind of surprised.
If you want to find out if the yeast are good, just make 2 cups of a starter wort at 1.040 with DME and water. 1/4 cup of DME brought to a boil in 2 cups of water. Let it cool to 75F and through your yeast in. If it ferments out and smells yeasty or like beer, it's viable.
You still need to practice good sanitation practices.
I have no idea why you'd need to do test viability though. I have never had a viability issue with my harvested yeast.
If the harvested yeast is less than two weeks old, I make a 1 liter starter (100 grams of DME to 1 liter of water brought to a boil, cooled, pitcch the yeast in and let it get happy. Without a stir plate, you need to pick it up and shake it up about once every hour or two (keep that schedule as best as you are able). To multiply yeast to their maximum they need oxygen. Unless it smells bad, it's good to go into your beer (poor sanitation practices is the only thing that will hurt you).
If the harvested yeast is more than two weeks old I'm in the habit of stepping the starter. The reason is because after two weeks you'll be getting some cell die off. Pitching dead cells isn't horrible, as dead cells are a nutrient, but I prefer not to have too many dead cells in my starter (based on % of cells dead vs. % of cells alive). I make the 100 grams of DME to 1 liter of water starter and put it on my stir plate. 24 to 36 hours later, I'll make another liter of starter wort and add it to what I have already going.
I have been known to not worry about the number of dead cells, especially in lower gravity beers (1.060 SG or less).
I've used yeast as much as 4 months old and my beers have all turned out great.
If you're concerned about over pitching, you can feed your yeast in advance. Let's say that you plan your brews out like I do. I'll have a recipe I'm going to brew three months later. I'll have harvested yeast that I plan on using. Three months in advance, I'll make a starter with it. Once it's finished fermenting out the starter wort, I'll put the flask in my refrigerator and let the yeast settle out. This will leave the yeast on the bottom and the beer on top. I'll be able to estimate the amount of yeast slurry I have by doing this. I'll then decide on how many pint canning jars to store it in. Let's say that I need two canning jars (I always have pint canning jars with sterilized water in them in my brew cabinet). I'll pull two down, remove the lids. I'll take the yeast and pour off the beer and then I'll add enough water from the two pint jars to equal two pints of yeast slurry and water. I'll pour the rest of the water out, then swirl up the yeast/water mixture and pour it into the two canning jars and seal them up. Put them in the fridge and wait until you're ready.
You've done some good things by feeding your yeast.
1. You've fed them and kept them from dying off for the time being.
2. You've increased your cell count, thus increasing your supply of yeast.
3. You've proven to yourself that they are still viable.
After you've used harvested yeast successfully over and over, you'll start to trust it just as much as you trust your fresh smack pack or vials.
I'm brewing tomorrow. I'm going to be using harvested Scottish Ale yeast (wyeast 1728) and it's the fourth time I'm using it. This yeast was originally pitched from a wyeast smack pack on June 9, 2013 into a RIS. I've only made Big beers with this yeast. This yeast has made three 5 gallon batches and been fed once. I had 11 pints of it last weekend. I've still got 9 pint jars of it in the refrigerator. I used 2 pints to get my starter going on Monday and I stepped it up to 2 liters yesterday morning.
Thanks for the feedback...
So now I'm planning on starting a new brew tonite I will be using the yeast I just harvested, if after 3 day I got no activity, can I pitch in a new package of yeast.
Sorry for all these questions and thanks again
It sounds like you just harvested. If you are brewing today, you've got nothing to worry about. I understand the angst that comes with your first harvesting. You dont want to risk it without knowing. Don't worry you are gonna be good.
I know it's too late to do this now but, for future reference, brew the same day you rack from the primary and, toss it right in. This is assuming you are brewing a similar style of beer that requires that type of yeast. I don't like to hold yeast if I don't have to. You can re-pitch that yeast over and over. I have done this I believe 9 times. It was a bunch. We just got tired of making things that require 1056.
Just pull it off the bottom of the previous batch and pitch it right into the new batch. Sanitize some sort of container (with boiling water or Star San) and collect the yeast. Then toss it in the new batch.