My limited knowledge of Fermaid K was from an interview Curt Stock did with Brad Smith about Mead. From what I've gathered it is just a simple yeast nutrient component that you can feed your yeast at specific times during fermentation. I'm not too sure adding this will make or break how your beer turns out unless you are making a Braggot or something really deficient in nutrients.
This short blurb written by Shea Comfort is taken from a More Beer Mead Making kit.http://morebeer.com/public/pdf/wmead.pdf
At the first signs of fermentation â€” Add 1 gram per gallon of Fermaid-K + 1â€“2 grams per gallon of DAP to the must. â€œGo-Fermâ€ by itself does not provide enough of the nitrogen and nutrients needed by the yeast in a honey must (honey is very poor in both), so DAP and Fermaid-K are added to makeup whatâ€™s needed. Fermaid-K provides a well-balanced, complete source of miconutrients, sterols, organic Nitrogen, and unsaturated fatty acids. Fermaid-K has some Nitrogen (24 ppm N for every 1 g/gal) but this is still not enough to supply the amount needed by the yeast. The rest of the required Nitrogen is made-up using DAP (50 ppm N for every g/gal). Mix the required amounts of Fermaid-K and DAP with just enough warm, clean water to dissolve the white crystals of the DAP and thoroughly stir it into the fermenting must.
Note: that the reason why the DAP and Fermaid-K are added now at the first signs of fermentation instead of at the beginning during yeast hydration or must preparation is two-fold:
1. During the hydration process the yeastâ€™s cell walls are not yet fully formed and at this early stage the form of nitrogen in the DAP (note: Fermaid-K also contains DAP) can actually burn the cell before it becomes fully formed. Later, once the cell wall has become fully formed and stabilized, it will then be able to handle the presence of the DAP.
2. The DAP and Fermaid-K could very well have been added as soon as the yeast was ready to be pitched into the must, however, other organisms could have used it as an energy source to gain a stronger foothold before the yeast had a chance to dominate the environment. To avoid this scenario, it is advisable to wait until the first signs of fermentation are visible, then add the nutrients. This way you are assured of feeding only the â€œguestsâ€ you actually invited to the partyâ€¦