Recently, James Spencer (host of the podcast Basic Brewing Radio) and I (Editor of Brew Your Own magazine) launched a plan to conduct a series of brewing experiments. These experiments would test various questions of interest to homebrewers. In addition, participating homebrewers would perform the same experiment as us, potentially strengthening the results of our experiment. Our first collaborative experiment involved testing the effects of leaving your beer on the yeast for extended periods of time. (Read the results in the September 2009 issue of BYO and hear our tasting and discussion of the experiment on the May 28th episode of Basic Brewing Radio.)
For the second experiment in the BYO/BBR series, we’ve chosen to test the effect of pitching rate on your beer. All brewing sources maintain that you should pitch an adequate amount of yeast to get good fermentation characteristics and great-tasting beer. But, how critical is pitching rate? We’ve designed an experiment to test this.
The Question and Common Wisdom
Our experimental question is: how does pitching rate affect your beer? Common wisdom tells us that a lower pitching rate results in a slower fermentation, lower attenuation and more esters. Very low pitching rates are also said to provide a window for contamination to take hold, because the yeast does not quickly colonize the wort and produce enough alcohol to inhibit other microbial competitors.
Higher pitching rates are said to result in a faster fermentations, higher attenuation and cleaner beers. Exceptionally high pitching rates are said to impart a character called “yeast bite.” Our experiment focuses on the expected differences and will attempt to quantify the degree to which these factors are influenced by pitch rate.
To test this hypothesis, we have a simple experimental design. There are quite a few options you could add to this experiment, but we’ll explain the basic idea first.
We suggest that experimenters brew 6 gallons (23 L) of wort. This wort will be split evenly between three fermenters. (Ideally, the three fermenters would all be of the same type.) One wort would be pitched with the recommended amount of yeast. We’ll call this the 1X trial. The other two fermenters will be pitched with 1/4X and 4X amounts of yeast, respectively. (In other words, a quarter of the recommended dose of yeast and four times the recommended dose.)
To arrive at the standard pitching rate, we’ll use Jamil Zainascheff’s pitching calculator -- found at mrmalty.com. For simplicity, we’ll weigh out the required amount of dried yeast. Assuming that a given weight of dried yeast will repeatably contain roughly the same amount of viable yeast cells, this should allow experimenters to reliably get fairly close to the calculated rates. (At a minimum, the relative yeast amounts should be correct.) For beers with a SG 1.048–1.056 (12–14 °Plato) original gravity (OG), 4 grams of dried yeast is recommended to pitch 2.0 gallons (7.6 L) of ale.
Options include reserving a small amount of unpitched wort as a control and/or pitching at 1/2X, 1X and 2X. And, of course, individual experimenters are free to try different experimental designs — perhaps 5 gallons (19 L) of beer split into five 1.0-gallon (3.8-L) jugs?
Data to Collect
We’ll collect a variety of data, both objective and subjective. Forms will be available online to fill out. We'll post a link to the online form on this blog and on basicbrewingradio.com. These will include spaces for all the relevant data plus room for additional comments.
Pitching rate is said to affect the rate of fermentation, so — for each of the three fermenters — we’ll record the time until fermentation starts and the time until fermentation is complete. When fermentations start and finish can be hard to judge. For this reason, we suggest picking an arbitrary set of criteria and applying it to all the fermenters. For example, let’s define the beginning of fermentation as the time when the top of the wort is completely covered with kräusen. (This will likely be after the first bubbles in the airlock appear.)
Likewise, let’s say that fermentation has finished when your final gravity is reached. (There still may be some bubbling in the airlock at this time, due to gas diffusing out of solution.) We recommend taping an index card or other piece of paper to each fermenter and keeping your records there as the experiment progresses. (This will also serve as label indicating the pitching rate employed in that fermenter.) We will also record the final gravity (FG) of each of the beers. If you miss the start or finish of fermentation, either report it as before or after a certain amount of time or don’t report the data. (In other words, don’t guess at the time or feel that missing it renders the rest of your data useless.)
Once the beers are packaged and conditioned, it will be time to collect the tasting data. (Remember to treat all three trial identically during packaging.)
Pitching rate is said to affect ester production. Esters contribute the “fruity” aromas to beers and are especially evident in ales. So, smell and taste each beer and rate them according to how fruity they appear to you. Likewise, see if you detect any differences in the body or sweetness of the beer. Both of these will be reported qualitatively. For example, you may find that beer #1 is the fruitiest followed by #2 and then #3. Or you may find, for example that number 3 is the fruitiest, and 1 and 2 exhibit the same level of esters. We’ll also measure the foam stand in inches and time until it collapses.
Finally, record any other differences you find between the beers. Are there any flavors or aromas that are found in only one of the beers? And finally, subjectively, do you find the beers to be overall fairly similar? Or does the pitching rate greatly affect the character? Which beer do you prefer?
OK homebrewers, let's get out there and advance homebrew science!