Re-Pitching Yeast, Boil Timing, Brewing Lagers: Mr. Wizard
Q
I am tired of buying yeast all the time. is it OK to just repitch the trub from a previous batch?
@dangerolsen
Via Twitter
A
Re-pitching of yeast is a normal method used by brewers around the globe. Although the practice is simple, there are a few rules that may make the method less than ideal for the typical homebrewer. The first rule is that the yeast should be harvested shortly after fermentation is complete and used within a short time period.
The most common method of yeast harvesting is by bottom cropping, because lagers are the dominant beer type in the world. Most commercial lager brewers these days bottom crop yeast from the bottom cone of cylindroconical fermenters and store it for short durations in a yeast brink (chilled and often agitated storage tank). Ale strains are sometimes bottom cropped and other times skimmed from the top of open fermenters, then stored in a similar fashion to lager yeasts prior to re-use.
There are a variety of ways to harvest yeast when homebrewing and the yeast can successfully be stored and re-used if you are careful. I suggest storing yeast in a flask and using cotton batting to close the top. Yeast stored in this type of container can be placed in a refrigerator without any problems for up to about 10 days before re-use. It is really preferable to keep this duration as short as possible since yeast viability and vitality decrease with time, especially as storage temperature increases. Ideally the storage temperature should be around 34 °F (1 °C).
Harvesting yeast for re-use at home has one major drawback and that is the fact that most homebrewers do not brew frequently enough to re-use for very long. Some brewers share yeast and are able to keep a culture going from one batch to another with short storage durations in between. This can work very well if you have a group of friends who are good, clean brewers.
Q
Does the amount of time it takes to get the wort to a rolling boil have a negative impact on the brew itself, or not?
Kevin Dill
Via Facebook
A
In a very general sense the time required to bring wort to a boil can cause problems when the time is too long. Holding hot wort for extended time periods leads to heat-related chemical changes, generally termed “thermal stress”. But in a more practical sense this is not normally associated with waiting for the kettle to boil for one very simple reason; evaporation rate.
Brew kettles are designed to boil and evaporate water from wort during boiling. Traditional, some would argue outdated, kettles are usually designed to evaporate about 8–10% per hour. More modern designs focus on reduced energy consumption and thermal stress during boiling, and the evaporative rates in these designs is usually around 4%. So how does this relate to kettle heating time? In order to achieve these evaporative rates a certain amount of energy must be supplied to the kettle and this amount of energy is plenty to heat the contents of the kettle to the boiling point during wort collection.
In practice, brewers do want to get the wort boiling as soon as possible to save time and also not feel like too much time is spent looking at a pot of wort waiting for it to boil. It does help to have a burner that can be cranked up for the heating stage and then dialed back once the wort begins to boil. If the burner is too small to get the wort boiling within 30-45 minutes of kettle full I would look for a larger unit that can provide more heat. One practical method used by most brewers during the brew day is to begin applying heat to the kettle during wort collection. If this is timed right the boil begins just about the time the kettle is full.
Q
I’m relatively new to homebrewing and want to try to brew a lager but I have been scared away by the temperature requirements. Without spending a lot, what are my best and simplest options?
Colin Oakes
Toronto, Ontario
A
One of the keys to brewing great lager beers, really, is keeping the fermentation temperature cool. There is no way to sugar-coat the importance of this fact. Lager beers that are fermented warmer than about 58 °F (14.5 °C) often have fruity aromas and sometimes have strong solvent and sulfur notes depending on the yeast strain. Here at Springfield Brewing Company in Springfield, Missouri, we brew several different lagers and the strain we use for fermentation works really quite well at 54 °F (12 °C). Some brewers prefer cooler temperatures for lagers, and the lower end of fermentation temperature used by commercial breweries hovers around 46 °F (8 °C). In order for commercial brewers to consistently achieve these cool temperatures, jacketed fermenters that are chilled with glycol or ammonia are required. Homebrewers often do something similar by placing their fermenter in a refrigerator to maintain a cool environment.
I think we brewers are often times spoiled by technology and too frequently equate old or traditional methods with being outdated, primitive or simply wrong. While there is no question that technology allows us to do things differently than our forerunners, there is also no question in my mind that brewers from the past brewed some very fine beers. You are in an ideal location to brew lagers like they were brewed prior to the advent of commercial refrigeration. And this is brewing during the months of the year that are cool enough for the type of beer you want to brew. By looking at the average highs and lows in Toronto, there are about four months of the year that have an average daily temperature in the middle of the sweet spot for most lager strains.
My advice on brewing lagers is pretty simple. Begin with healthy yeast and pitch plenty of it. Targeting 15 million cells per mL of wort is a good rule of thumb pitching rate for normal gravity beer. If you pitch with a slurry that has a normal cell density of about 100 million cells per mL, you will need 3 liters for a 20-liter batch size. For all those gallon users, sorry for switching units, but I cannot think in gallons of wort when cell densities are also reported using metric terms. Three liters of yeast seems like a lot of yeast, but the numbers don’t lie. Proper pitching rate is a great start for great lager.
The second half of this piece of advice is to give your yeast the building blocks required for proper growth, and this means properly aerating your wort. If there is one gizmo every brewer should build or buy sooner than later it is a wort aeration device. During growth yeast cells need oxygen to synthesize sterols and unsaturated fatty acids, both of which are important constituents of cell walls.
And finally, let the fermentation take off in a cool environment with a maximum temperature not warmer than 54 °F (12 °C), and no cooler than about 45 °F (7 °C). This very well may be the average temperature of your garage. If you follow these three simple pieces of advice your lager fermentation should be complete in 10 to 14 days for brews with an original gravity in the 12 to 15 °Plato (1.048 to 1.061 SG) range, and longer for higher gravity beers. After fermentation is complete there are multiple options for packaging and cold conditioning, but these are not as critical to defining the beer flavor as is fermentation. Focus on the fermentation of lagers first, and the rest of the process will be become more apparent the more you brew and the more comfortable you become with these types of yeasts.
Q
A commercial brewer recently told me that he is concerned that volatile organic compounds from wildfires in the Pacific Northwest will condense on hops and alter their organoleptic properties. Is this a real possibility? Assuming it is, how might the tainted hops affect beer?
Greg Lewis
Idaho Falls, Idaho
A
I know that wine grapes grown near eucalyptus trees can pick up enough eucalyptus oil to impart the aroma to wine. So it is does seem possible in theory that hops grown near wildfires could pick up enough smoke from the air to taint the aroma of the hops. I know that some western areas of the United States had a bad wildfire season this year and that the smell of fire and resultant ash was a nuisance to residents living nearby. As it happens, some wildfires in Washington were relatively close to hop farms.
To answer this question I looked in brewing texts and online for references about wildfires affecting hops and came up empty handed. So I then asked a friend and colleague in the brewing industry who works for Roy Farms in Moxee, Washington, if he knew anything about this topic. Roy Farms is one of the largest hop farms in the world and is located in the Yakima Valley. The answer I got in response to this question was very positive to brewers; the smoke concentration required to impart smoky aromas to hops would have to be so high as to be lethal to humans and other mammals living near the hop fields. The good news is that there have been no deaths around Washington hop fields attributed to smoke from wildfires, and thus no smoke effect on the hops either.
I thought this question seemed to meet the litmus test of something falling into the realm of the possible, but based on my limited search it seems that this may be one of those things not to lose sleep worrying about.
