Understanding Attenuation in Home Brewing

We recently brewed a maibock using Rogue’s Pacman yeast as distributed by wYeast that we picked up from the nice folks at Homebrewer’s Outpost.

Today when we checked our gravity after about 5 days of fermenting we were a bit below our goal of 1.016, coming in at about 1.023. Knowing that PacMan yeast is supposed to attenuate quite well I was curious as to what caused the yeasts to be so bashful at the dinner table. Our temperature was decent at about 68*, I made a good sized starter, so what was the problem?

I checked out the wiki at homebrewtalk.com and read over their page on attenuation. Using a formula I got from that page

Attenuation = 100 % * (starting gravity – current gravity) / (starting gravity – 1)

I realized that our attenuation was about 62% as opposed to the 74% we were shooting for. Further down the page I came across the following:

water to grist ratio: the enzymatic activity of the amylases is affected by the thickness of the mash. Thinner mashes enhance the maltose production and therefore increase the fermentability. See The Theory of Mashing.

We had indeed gone short on this. When we did our first few brews we followed Papazian’s recommendation of 1qt/lb of grain. After a few brews we started noticing that 1.5qt/lb was actually giving us a better brew. But, as is sometimes the case, we flaked on our math and wound up reverting to the 1qt/lb. We noticed this and took note, but had little idea how this would effect our beer. Now it’s clear that a higher water to grain ratio is preferred in order to increase the fermentability of your beer.

Duly noted.