My daughter gave me two Brewer’s Best kits for my birthday. One is a Russian Imperial Stout (1.078 OG), and it came with one pack of 11.5g yeast. When I plug this in to Mr. Malty, I get back that I need approximately 5g more yeast. I’ve seen this with all kits, i.e., one pack of dry yeast as default. Why is that? I do remember brewing my first several batches with just what came in the kit, and it came out ok, but if the brew needs more yeast, why not put that in the packaging? Just curious. Thanks.
There’s many reasons why two packets of yeast aren’t included. Most importantly is that the cost of the kit will rise deterring potential buyers while giving little benefit to the resulting beer.
Yeast calculators are subjective. Some overshoot, some undershoot? There are at least three well known formulas for determining yeast cell count needed in a brew. It’s doubtful that a well know kit manufacturer would short yeast in their kits if it really is needed.
Yeast is readily available at the homebrew store where you purchased the kit and if you really wanted to ferment the kit with the calculated amount of yeast, an extra packet could easily be purchased along with the kit, placing the burden of the extra yeast packet onto the consumer and homebrew shop owner.
Your beer should turn out fine with one packet. It might turn out better with two. The main reason for the extra yeast in a strong beer like a RIS is that the high specific gravity is tougher on the yeast so there may be extra lag time before fermentation begins. If it begins fermenting quickly then it will be fine. If there are no signs of fermentation after about 36 hours then you should add more yeast to prevent contamination. The longer the wort sits before fermenting, the higher the chance of off-flavors.