When you use tired old yeast, would it be better to make a starter?
Talking of yeasts, there was an interesting comment on effect of rapid temperature change on yeast from one manufacturer data sheet I read (Lallemand). On reconstituting yeast, they wanted you to do it at 85-95 deg. then cool gradually to wort temp 5 min per 10 deg, using small amounts of cool wort.. Their assertion was not that the cells got killed, but that rapid temp changes cause UNWANTED MUTATIONS, potentially causing off flavors.
I usually just sprinkle it onto the wort though it seems to work but I am not sure of the impact on the yeast rehydration process - and how much better my beer would be if I followed their process.
***************************************************** Some Yeast Facts *****************************************************
Lallemand data sheets are interesting to me, for example they illustrate difference between the yeasts and why they behave differently.
Why choice of yeast affects beer sweetness and attenuation.
e.g. London which they say will not eat maltotriose sugar, leading to the sweeter beers,
"London does not utilize the sugar maltotriose (a molecule composed of 3 glucose units). Maltotriose comprises an average of 10-15% of total sugar in all-malt worts. The result will be fuller body and residual sweetness in the beer. Be advised to adjust gravities and mash temperatures according to desired result. "
(If you pick the yeast in Brewers Friend calculator it does this compensation for yeast sugar usage for you.)
or Belle Saison which they say is a variety diastaticus.
"Saccharomyces cerevisiae var. diastaticus strains are capable of utilizing some types of dextrins. Extra care should be taken to ensure proper cleaning procedures are in place to avoid any cross-contamination with other brews. "
I put some by accident in a brew of Sticky Wicket stout and it was very dry tasting.
Choice of yeast affects Dry Hopping
Also they describe the different effects for dry hopping incising different yeasts. Some yeasts produce chemicals that accentuate hop flavor.
This is a fascinating paper detailing effect of various hops and transformation of the desired flavors, and includes the use of coriander as a source of chemicals for yeast transformation into similar flavors. Don't be put off by the chemistry speak, skim to find the conclusions (unless you are chemistry geek lol).
Rehydration guidelines are quite simple and present a much lower risk of contamination than a starter, which is unnecessary when using the recommended pitch rate of dried active yeast.
Sprinkle the yeast on the surface of 10 times its weight in clean, sterilized water at 30-35°C (86-95F). Do not use wort, or distilled or reverse osmosis water, as loss in viability may result. Stir gently, leave undisturbed for 15 minutes, then stir to suspend yeast completely. Leave it to rest for 5 more minutes at 30-35°C.
Without delay, adjust the temperature to that of the wort by mixing aliquots of wort with the rehydrated yeast. Wort should be added in 5 minute intervals and taking care not to lower the temperature by more than 10°C at a time. Temperature shock of >10°C will cause formation of petite mutants leading to extended or incomplete fermentation and possible formation of undesirable ﬂavors. Do not allow attemperation to be carried out by natural heat loss. This will take too long and could result in loss of viability or vitality.
Inoculate without delay into cooled wort in the fermenter. Belle Saison yeast has been conditioned to survive rehydration. The yeast contains an adequate reserve of carbohydrates and unsaturated fatty acids to achieve active growth. It is unnecessary to aerate wort upon ﬁrst use.
It may be carbonated adequately at 2 weeks, but the 4 weeks gives the yeast more time to clean up any off flavors.
And be patient, give it 3 days in the fridge before opening it for best results - this impacts proper absorption of the carbonation. If you are really impatient, put several in and you can hopefully see the difference over the few days. If you see no difference I guess it won't matter for you.