Dear Mr. Wizard,
I have been brewing for 3 years and all of my beers have been ales. For my most recent 2 batches, I have decided to go with lager yeast. When brewing the first batch, I pitched the yeast at 70° F and put an airlock on. On the second batch, I pitched the yeast at 50° F and put an airlock on. For both batches, it took five days for the yeast to start fermenting. The first batch turned out fine, and the has started to ferment. Could the slow start in fermentation be caused by putting an airlock on too early and the yeast not getting enough oxygen? Do you have any suggestions?
Mr. Wizard replies:
The main factors that influence the "lag" time between pitching yeast and the onset of vigorous fermentation are pitching rate, wort aeration and wort temperature. When seasoned ale brewers, like yourself, brew lagers they often make the mistake of simply switching yeast strains and fermentation temperature.
In my experience, lagers ferment much better when a higher pitching rate is used. For example, many commercial ale brewers use between 5 and 10 million yeast cells per milliliter of wort while lager brewers typically use between 15 and 20 million yeast cells per milliliter of wort. Homebrewers do not usually count yeast cells like commercial brewers, but given the same type of yeast slurry thickness, you would need to double or triple your pitching volume to get these results. My comments on pitching rate in the past have generated some debate by those who feel my advice is a bit extreme, but it is my experience that many brewers add insufficient amounts of yeast. Your description of the slow start sounds like a classic case of under-pitching.
Wort aeration also has a dramatic influence on the length of the lag time because oxygen is used by yeast for growth. Low wort-oxygen levels translate to decreased yeast growth, lower peak-cell density in solution and hence longer fermentation times. The best methods for aeration all utilize some device to actively transfer oxygen into wort, such as an aeration stone. Simply splashing the wort as it enters the carboy is not as effective as an aeration stone, and relying on oxygen from the atmosphere to diffuse into the wort by leaving the airlock off for some period of time is the least effective method of aeration. If you are using the latter technique your slow starts could certainly be due to poor aeration. I would advise using a different method and putting the air-lock on immediately to minimize the risk of contaminating your wort with airborne microorganisms.
Finally, there is the temperature variable. Some lager brewers like to add plenty of yeast, begin fermentation between 46° and 48° F and allow the fermentation to rise to about 52° F. These brewers feel this method produces the cleanest lager flavor. Other brewers advocate beginning fermentation around 70° F and cooling it down to around 52° F after fermentation begins. This method is used to compensate for lower cell densities by stimulating yeast growth. I have experimented with various methods and have found that some lager yeast strains are more finicky than others and really do not work well with cool starts. The lager strain I most frequently use is a German pilsner strain. It works best for me if I use a healthy pitching rate and begin fermentation no cooler than 52° F. I typically see active signs of fermentation within a day of pitching, and primary fermentation is usually complete within 14 days.
Dear Mr. Wizard,
Is secondary fermentation necessary or even desirable for all styles of beer. My local homebrew supply shop (and microbrewery) advised that, unless I plan on dry-hopping, I shouldn't use a secondary fermentation. Their main objection was the unnecessary risk of contamination. Are there other benefits besides dry-hopping and clarification in using a secondary fermentation? If I were brewing a stout, I obviously wouldn't be dry-hopping or concerned with clarity. Would I be okay just using a two-week primary fermentation and maybe dropping the temperature a bit after 5 to 7 days for the remainder of the 2 weeks before bottling/kegging?
Mr. Wizard replies:
I like this question because it contrasts the conventional wisdom of homebrewers, who almost always refer to primary and secondary fermentation, with commercial brewers, who ferment in "uni-tank" fermenters. To be honest, I have never understood why the homebrewing vernacular uses the term "secondary fermentation" to describe the aging process. Typically, when wort is fermented in the "primary fermenter" it ferments completely. The specific gravity ceases to change after a week or two, and then it is transferred to the "secondary fermenter" for aging. If the beer is transferred to the secondary after fermentation is complete there will be no "secondary fermentation." The true second fermentation occurs when priming sugar is added to the beer at the bottling stage and the result of this second fermentation is carbonated beer.
Historically, most commercial brewers used a primary fermentation vessel (open or closed) to completely ferment their beers and then transferred the young, flat beer to a conditioning vessel for aging. Lager brewers typically would add kraeusen (young fermenting wort) at this stage and ale brewers would add priming sugars. The beer would clarify, carbonate and age during this secondary fermentation. Then the beer would be filtered (if the style was filtered) and bottled or kegged.
These days, uni-tank fermenters have gained popularity and the fermentation process has been simplified. Fermentation and aging are conducted in the same vessel. Many brewers "cap," "bung" or "spund" the fermenter when the specific gravity is about 1°Plato (1.004 SG??)above the expected final gravity. This technique allows for natural carbonation and the devices used can be adjusted to vent excess pressure from the fermenter, allowing control of carbonation level and protection against over-pressurizing the tank. Most uni-tank users hold the beer at fermentation temperature for a few days after fermentation is complete for diacetyl reduction and then cool the beer either slowly or rapidly depending on the particular brewery. After the beer has been aged it can be filtered if desired and packaged.
A typical timeline for a uni-tank ale would be a 5-day fermentation capped after about 3 days, followed by a 2 -day diacetyl rest, then by a week at near-freezing temperatures. Uni-tank lagers may ferment for about 10 days before capping and usually are lagered for about a month before filtration and packaging. The great thing about uni-tanks is that they have conical bottoms allowing the yeast to be removed shortly after cooling for re-use. Some brewers periodically purge the cone of yeast sediment during aging to reduce off-flavors associated with yeast autolysis. Most microbrewed beers you drink are probably made using a similar method to what I have described and most likely have been exposed to yeast sediment during aging. Beers that are dry-hopped are either transferred to another tank with the hops placed in the tank prior to transfer (or the hops are added to the uni-tank from the top after fermentation is complete.)
I have made many 5-gallon batches of beer in a single carboy with great success. I have also fermented a lot of beer in uni-tank fermenters with equal success. I agree with your local homebrew shop that a secondary fermenter is not required to make great beer. Furthermore, it is possible to produce very clear beer in a single-vessel process if you cool the beer prior to racking it to the bottling bucket or keg - provided that you are careful and skillful during the racking process.
Give it a try and see how it works for you! If you like the beer produced by this method, you have one less fermenter to clean and sanitize per batch and you only have to rack the beer once.
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