Fyfo writes the following, and a good job of it he does as well, I have added the other users methods as well.
Here is a post for activating your yeast before adding to a wash.
Why do we do this? Yeast is an amazing thing, but it gets stressed when exposed to the wash Luckily we can help it out by "activating" it first. "Activating" basically begins a process of allowing the yeast to reproduce in a stress free environment so we can maximise it's conversion of sugars to alcohol as quickly as possible and with minimum off flavours (caused by stressed yeast).
This is what I have been doing with great success so feel free to try it and see if it works for you...
I make up my wash as per the recipe and take an SG reading. I try to ensure the temperature has been adjusted with hot and cold water to reach mid twenties to low thirties (I mainly use bakers yeast). Then I extract around half a litre of the wash in a five litre jug. Then I add in the yeast (I aim for 75g per 25 litre wash) and stir thoroughly. I leave this for around an hour and find the yeast has grown exponentially and fills the jug with a browny yellow froth. Never put the lid on the vessel/container!!
Give the wash a really good stir to aerate it and now the yeast can be added to the wash. I don't stir it in.
I would take this a step further and Rehydrate the yeast first.
This means filling a jug (or whatever) with about 300ml of warm water.
Sprinkle the yeast on the top - and DONT STIR.
Leave it for 30 minutes to allow the cells to absorb water , Then stir gently to form a slurry.
Then add it to that 500ml wash sample and allow it to activate.
This way you can use less yeast - it will multiply to suit and wont taint the wash with stressed yeast flavours as you say
That initial stirring before it hydrates will kill off half the yeast cells before they can do anything.
This is the method recommended by the yeast producers for wine and should be done this way for our system too.
Nixon/McGraw say in The Compleat Distiller,
Yeast re-hydration Active dry yeast is often not properly re-hydrated. The first few seconds of re-hydration, as the cell walls re-constitute themselves, are critical to the survival of the yeast. Re-hydrating at too low or too high a temperature will cause a large percentage of the added yeast to be sickly or die, resulting in slower than expected fermentation. The same effect is caused by excessively high sugar concentrations at the beginning of the fermentation. This can cause up to 80 % of the added yeast to be unhealthy and die early in the fermentation. Proper re-hydration technique for active dry yeast is: • 1 part by weight to 5 parts sterile (boiled) water (e.g. 50 gm yeast is re-hydrated in 250 ml. Water). • Initial water temperature 38º - 41º C (100º - 105º F) • Mix well, and allow to sit for at least 10 and not more than 20 minutes before adding to ferment. CAUTION! This procedure is for pure, active dry yeast, and should not be followed for yeast products that contain nutrients. These are formulated for specific method of use, so be careful to follow the package directions.
Chugalug chips in with this,
When using an expensive yeast, I seldom have enough according to the packaging, always only using one pack whether it's 20l or 80l, so this is my protocol, especially when I'm under-pitching.
Oxygenate the water.
Raise temperature to 40C.
Sprinkle yeast, wait at least 10 minutes. 20 minutes is too long.
Feed the yeast by adding wort, must, wash, or some of the ingredients, juice, molasses, malt, sugar, etc.
When the wash is ready, pitch if the temperatures are close. If not, feed the yeast a spoon of the wash, put it in a plastic bottle, shake to aerate, float it in the fermenter until the temperatures are closer, then pitch.