Why is rehydrating the dry yeast before pitching important?
Dry beer yeast needs to be reconstituted in a gentle way. During rehydration the cell membrane undergoes changes which can be lethal to yeast. In order to reconstitute the yeast as gently as possible (and minimize/avoid any damage) yeast producers developed specific rehydration procedures. Although most dry beer yeast will work if pitched directly into wort, it is recommended to follow the rehydration instructions to insure the optimum performance of the yeast.
Does foam or no foam during rehydration give me an indication of how actively the yeast will ferment?
No! There is no definite explanation why some dry yeasts foam more than others but it has been proven in a series of tests that the occurrence of foam during rehydration is not an indication for more active yeast. Yeast that produced large amounts of foam could have poorer activity than yeast that did not produce any or only small amounts of foam.
Should I refrigerate or freeze my dry yeast until I use it?
Yes, although dry yeast can be stored at room temperature and performs well for the duration of the shelf life it is preferable to store it at colder temperatures. Dry yeast will always lose some of its viability and activity over time but at colder temperatures these losses are less than at warmer temperatures. If you choose to freeze your dry yeast for storage, let it warm to room temperature in the package before rehydration & pitching.
I am making a high gravity beer. Does this affect the amount of dry yeast I should add to my wort?
Yes, for high gravity beers the pitching rate should be increased. The rule of thumb is one million cells per degree Plato per ml. Under-pitching can result in slow or stuck fermentation.
What will happen to my beer if I add too much or too little yeast?
The pitching rate influences the lag phase and general fermentation speed as well as the flavour of the finished beer. Too low pitching rates will result in longer lag phase and higher risk of contamination as well as longer overall fermentation time. Too high pitching rates speed up the fermentation but can lead to early autolysis.
Do I need to use nutrients when using dry brewing yeast?
Like any yeast, dry beer yeast benefits from additional nutrients. In particular, when brewing high gravity beers or using larger amounts of adjuncts, the wort needs to be supplemented with extra nutrients to ensure optimum yeast performance.
I always aerate my wort when using liquid yeast. Do I need to aerate the wort before pitching dry yeast?
No, there is no need to aerate the wort but it does not harm the yeast either. During its aerobic production, dry yeast accumulates sufficient amounts of unsaturated fatty acids and sterols to produce enough biomass in the first stage of fermentation. The only reason to aerate the wort when using wet yeast is to provide the yeast with oxygen so that it can produce sterols and unsaturated fatty acids which are important parts of the cell membrane and therefore essential for biomass production.
If the slurry from dry yeast fermentation is re-pitched from one batch of beer to another, the wort has to be aerated as with any liquid yeast.
I have a package of dry yeast that is 6 months past its expiration date. Can I still expect it to work?
Although the yeast might still be viable and active, there is no guarantee that it will perform as well as yeast within its expiration date.
How does changing the fermentation temperature change the “dry” or “fruity” character of my beer?
At warm fermentation temperatures, more esters and higher alcohols are produced than at colder temperatures, resulting in more fruity, floral flavors.
Can I re-pitch the yeast slurry from one batch of beer to the next? If so, what would you suggest regarding the amount of times I can re-pitch before I start with a fresh package of dry yeast?
Slurries from dry yeast fermentations can be re-pitched like any other crop yeast. Before re-pitching the yeast viability (stain with methylene blue) and microbiological cleanliness (using specialized laboratory media from Siebel Institute of Technology) should be verified. Because each re-pitching increases the risk of contamination and viability and vitality of the yeast can decrease with each generation (depending on beer style and fermentation conditions), re-pitching should be limited to maximum 5 generations.