Dear Mr. Wizard:
I am brewing a batch of "honey brew" using 6 pounds of amber extract and 2 pounds of honey. I purchased Wyeast 1056 (American Ale yeast) in the 6-ounce size. The package said the yeast was "pitchable" but I stepped it up anyway. Actually, I stepped it up twice: first to about a pint (approximately 1.033 gravity) and two days later to a little less than two-thirds of a quart (1.050 gravity). I brewed everything, cooled it off, and pitched the yeast into my 6.5-gallon carboy.
This is the first time I have used a glass carboy, instead of a 7-gallon bucket. I still chose to use the airlock, never thinking the krauesen would fill the remaining 10 inches of headspace in the carboy. The next morning I got up and found the headspace filled to capacity with krauesen. It was also spewing out of the air lock! Can you step up yeast too much? What are my chances of contamination? I immediately sanitized some hose, a brass coupling and another stopper and set up a blow hose. Your insight would be graciously accepted.
Vance J. Stringham
Mr. Wizard replies:
Although you had a giant mess on your hands with your excited fermentation, you may have added a normal amount of yeast. In my experience, small yeast packets do not contain enough yeast after they swell to contribute a proper pitching rate to a 5-gallon batch of wort. My opinion is based upon observing the vigor of fermentation as well as performing cell counts on yeast from smack-packs with a microscope. Stepping up the pack is a good idea, although one step would have done the trick. My suggestion would be to propagate the yeast in two quarts of 1.048 wort, allow the fermentation to finish, decant the beer above the yeast and pitch the concentrated yeast solids. One to 1.5 cups of yeast solids per 5 gallons of wort is a good pitching rate.
Now the bad news: The krauesen spewing out of your carboy is directly related to your pitching rate. A wimpy rate usually results in a thin krauesen that will rarely leave the fermenter. Air locks can vent the gas from such a fermentation. Increasing your pitching rate increases fermentation rate, decreases certain aroma compounds, decreases the chance of contamination ... and increases the odds of making a mess!
The minimum precaution when fermenting in a carboy is to attach a blow-off hose. Still, I don't think you contaminated your beer by neglecting to use a hose. Any microscopic invaders were most likely pushed onto your floor along with the krauesen. Usually the headspace provided by a 6.5-gallon carboy is plenty for a 5-gallon fermentation, but sometimes foam happens!
Dear Mr. Wizard:
I just brewed an all-grain amber recipe from the May 1999 issue. This was my third all-grain attempt, and it raises a few questions. Since I started using a 100,000-BTU burner, I end up with a smaller volume than the recipes anticipate. I know this is due to a more aggressive boil, but I am concerned with having to top off my fermenter. Is this a problem? Should I start with more wort? Also, the recipe calls for the gravity to start at 1.064. My yield prior to the boil was 1.042. Does it change during the boil? Should I check it again after topping off to 5 gallons?
Salt Lake City, Utah
Mr. Wizard replies:
Recipes printed in BYO give the "original gravity" of the wort. This number refers to the specific gravity of the wort prior to fermentation-in other words, after the boil. Wort gravity increases during boiling because the wort is concentrated as water is evaporated. Most commercial brewers want to evaporate at least 8 percent of the wort volume during boiling to ensure adequate removal of volatiles, such as dimethyl sulfide. Excessive evaporation can result in the formation of unwanted flavors. It also wastes energy. Energy is not a huge concern with homebrewing, but imagine a commercial brewkettle with a pre-boil volume of 800 barrels (24,800 gallons). A typical boil can evaporate 64 barrels (1,984 gallons) of water in 60 minutes! That requires a lot of energy.
For starters, to hit the target gravity and the target volume of a recipe you must know the efficiency of your brewing system. If you don't know your efficiency and strictly follow a recipe, you most likely will miss one of your targets. If your system is very efficient, you may hit the gravity target by over-shooting the volume target (by the way, adding water after the boil causes no problem as long as it is pre-boiled). Missing your target volume may not seem like a big deal, but it affects the bitterness of the final beer. More beer means a dilution of the hop bitterness. The bottom line is that getting a handle on your efficiency will help you. Your target was 1.064 post-boil and you had 1.042 pre-boil (which translates to about 1.050 post-boil); this indicates that your system may yield less from the malt than the recipe you followed.
Another technique you may want to adopt is tracking your evaporation. You can do this by calibrating your brew kettle and noting the pre- and post-boil volumes. Here's the formula to use:
Evaporation percent = 100 - (post-boil volume x 100 ÷ pre-boil volume).
For example: Say you collect 5.5 gallons of wort and boil it down to 5 gallons. This would be 100 - (500 ÷ 5.5), or 100 - 90.9, which equals an evaporation rate of 9.1 percent.
Most commercial brewers target between 8 and 10 percent evaporation during the boil. For homebrewers, a good evaporation rate is 6 to 8 percent per hour. A kettle that evaporates 6 percent per hour will evaporate 8 percent of the volume in 80 minutes. If another kettle evaporates 8 percent per hour, then a 60-minute boil will evaporate the same wort volume. As you collect more data, you can adjust your flame to fine-tune your evaporation rate. If you don't like topping off your batch with preboiled water, tweaking your boil is an easy way to eliminate this practice.
Mr. Wizard, BYO's resident expert, is a leading authority in homebrewing whose identity, like the identity of all superheroes, must be kept confidential. To see more of Mr. Wizard, check out the latest issue of Brew Your Own at better homebrew shops and newstand locations.