lucas said:
just to clarify, im asking about SAFale Vs. the yeast from a bottle of coopers pale ale, not the coopers dry yeast.
I've only done one brew with the dry coopers yeast and it was crap, but to be fair that was probably more an issue of temp control and using coopers "brewing sugar" instead of malt. i have plans to do a controlled "budget brew" some day soon, tin of the farmland draught, some dextrose and perhaps ill use the coopers dry yeast (since im building up quite a supply of it) and see how it turns out when its not brewed at 28-30 degrees.
on another (completely unrelated note), if autolysis is what happens when yeast eats dead yeast; and boiling yeast kills it, why do people consider boiled yeast "yeast nutrients"? isnt that just paving the way for autolysis?
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I've used Safale S-04 in the past on stouts with pretty good results - IMHO. I like the fast finish of this strain and the slightly fruity notes that this yeast gives. Well worth a try and is heaps better than the sachet of yeast nutrient that Coopers kindly provides with their kit concentrates...
Re your question on yeast autolysis and boiling yeast as nutrient, there are slightly different things happening to each of these batches of yeast which makes it worthwhile using the dry kit yeast in this manner. The hard part is trying to describe the differences without going into total beergeek mode!
h34r:
//engage beergeek mode//
Yeast require a number of nutrients for growth, including vitamins, minerals, carbs, nitrogen and trace elements (including copper and zinc). A good source of nitrogen comes from the amino acids found in the wort. Yeast cells use the nitrogen to develop cell proteins and other compounds. There are roughly 20 amino acids and they are commonly found in the malt extract / wort that we use in beer brewing. All of the wort amino acids and the small peptides are referred to as Free Amino Nitrogen or FAN. The FAN level in your wort is a good indicator of potential yeast growth and therefore fermentation performance. Cheap malt extracts are often low in FAN. A typical all malt freshly mashed wort has around 150 to 220 mg of FAN per litre. So any decent yeast nutrient should contain FAN...
Now, yeast has FAN levels of around 2% by weight, so, if you want to increase the FAN levels in your wort, you could toss in some yeast in the boil (I normally add it with about 10 mins to go). Ok so it doesn't add all that much FAN but it does also add some zinc to the brew - which is an important yeast growth contributor - and whilst it's not a lot, it's better than tossing the sachet into the bin...There are other contributors that the yeast cells surrender, such as Vitamin B, but I think you get the point without boring you with too much more detail!
The boil does kill the yeast and it violently erupts the cells - as opposed to the cell breakdown via autolysis - so the boil assists by releasing nutrients into the wort from within the cells and even the cell walls themselves, which will help the fermentation yeast that's eventually pitched after the wort is chilled. Some brewers add modest quantities of bakers yeast to their boil to provide a relatively cheaper nutrient to brewing yeast...
An alternative to this rather murderous endeavour is to purchase some true yeast nutrient, typically food grade mono or di-ammonium phosphate which is a good nitrogen source.
A note of caution - don't just buy kilos of bakers yeast or yeast nutrient and upend it into the kettle - too much of this stuff will result in a horrid undrinkable and potentially dangerous beer.
Yeast autolysis (aka auto-self-lysis-splitting) , in very general terms, occurs when the existing yeast cells run out of sugars to consume in solution and the cells die through the action of their own enzymes which break down the cells structural molecules in order to find further nutrients - ie, it suicides out of starvation! It can occur if you left the yeast in the fermenter for an extended period of time, long after the fermentation had concluded. To avoid autolysis in the bottled product, it's wise to make the yeast cells dormant - by refrigeration, or, by pasteurising the beer and removing the yeast altogether from the brewed beer, or by racking the beer to reduce the cell count in suspension. Yeast autolysis does add significant levels of amino acids to the beer, as the walls rupture, but at this stage of the fermentation process, you wouldn't want to introduce amino acids (which tend to add to a fuller mouthfeel in the beer) via this process as the autolysing yeast adds substantial sulphur compounds to the beer and you'll get off flavours and a vegemite or meaty smell to the brew that may be impossible to remove.
So boiling dry yeast can potentially add yeast nutrients, whereas yeast autolysis occurs when the yeast cells run out of sugars to ferment and the cells self destruct.
Sorry about the long post (again!),
Cheers,
TL
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