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> Yeast Lag Phase, contributed by Aeneas
cj in j
post Feb 26 2005, 06:58 PM
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Yeast Lag Phase FAQ
Submitted by Aeneas

It has been some time since you pitched your yeast and you are not seeing any signs of fermentation, is it time to worry, repitch, add dry yeast, or is the batch ruined? In this FAQ, topics relating to the initial stages of fermentation will be addressed so that you, the brewer, can make an informed decision as to how best to proceed.

I want to reiterate the importance of proper sanitation in brewing. Your wort is at its most susceptible before fermentation begins, thus cleaning and sanitizing your fermenter and anything that will touch your beer after the boil is critical to prevent unknown microbes from invading your wort and spoiling your beer. I firmly believe that proper sanitation is the most important and often underappreciated aspect of homebrewing.


Q: It has been XX hours since I pitched my yeast, and I have not observed any signs of fermentation (krausen, airlock activity etc.). Is my beer ruined?
A: First, relax, no, your beer is not ruined. There are two aspects as to why you may not be observing fermentation, mechanical and biological. Mechanically, you need to confirm that all the seals around your fermenter are tight. This means that if you are using a bucket, that the lid is properly affixed and sealed well (I make sure that the lid is seated by striking the rim of the lid with the palm of my hand), and that the airlock has liquid in it to the levels indicated by the lines on the airlocks themselves. If you are using a blow off tube make sure that the tube seats well in the fermenter and that the free end is immersed in water. Mechanical issues more often than not are not responsible for a ruined batch of beer. Biological issues can range from insufficient pitch count to dead yeast and will be addressed below.

Q: After I pitch my yeast, how long do I have to wait before I see signs of fermentation?
A: The lag period of fermentation can vary substantially. It depends on many things: nutrient level, dissolved oxygen content, yeast viability and pitch count to name a few. Initially the yeast are replicating, and in doing so require oxygen and nutrients to make more yeast cells. The number of viable yeast cells will affect this because only viable yeast cells can reproduce. Thus, pitching a fresh starter of sufficient size for your batch is highly recommended (see cj_in_j's Cold Pitching FAQ). The important thing at this stage is to be patient, yeast are hardy creatures and will eventually begin fermentation when the number of yeast cells in the fermenter is high enough and the dissolved oxygen has been depleted. I have never had lag time more than 48 hours, even when pitching a liquid yeast pouch without a starter, so I would say that if it has been more than 2 days since you pitched, you should consider repitching.

Q: Are my yeast dead?
A: Probably not. The only way you would have killed your yeast would have been to pitch them into wort that was too hot. As a general rule, if your wort is below body temperature, it is OK to pitch your yeast. A quick gauge of this can be made by comparing your forehead temperature to that of your fermenter using the palm of your hand, however, pitching your yeast into wort above 80░F is not recommended. Adhesive thermometers similar to those used in fish tanks are available for homebrewing and are useful to determine if your wort is at a good pitching or fermenting temperature.

If you went to the other extreme and chilled your wort too much before or after you pitched your yeast (put it in a fridge or left it outside in the snow, for example), the yeast will go into cold shock and just sit there, not really growing or reproducing, just waiting for the temperature to warm so they can take off. This problem is often associated with lager beers as many people chill their wort to lager temperatures right away and aim for the low end of the spectrum. If brewing a lager beer, a large starter is highly recommended to get rapid fermentation. The yeast from a one-gallon starter is generally sufficient. If a starter is not used, I recommend pitching your yeast at room temperature then slowly, over the course of 3-4 days bringing the beer to fermentation temp. This will give the yeast enough time to get off on the right foot but will not cold shock them into slow growth.

Q: It has been 48 hours and I don't see airlock activity, should I repitch? What strain should I repitch with?
A: I advocate repitching after 48 hours ONLY if you don't observe any fermentation. One test that you can do yourself to determine if fermentation is happening or has happened (in some low gravity beers, you might have missed it) is to swirl the fermenter -- if you see bubbles coming from the airlock, you can be fairly certain that CO2 production, as sign of both aerobic and anaerobic respiration, has or is occurring. Another route would be to swirl the fermenter, remove the airlock and sniff, you should sense CO2 as a very astringent and irritating odor. Take a hydrometer reading to confirm.

If you had poor viability or pitched too hot, your yeast might be toast, so it may be time to consider repitching. I generally keep a couple packets of dry ale and lager yeasts in my refrigerator for these situations. Try to match the dry yeast to the brew, if it is an English beer style, an English-style yeast, for a German and American ales, Nottingham or Coopers are good dry yeasts. They may not be exactly what you want, but will salvage a batch if you are to this point. It is better than tossing the batch out.

Q: What affect do long lag times have on my finished product?
A: The biggest risk from a long lag time is contamination. As I have mentioned in the introduction to this FAQ, proper cleaning and sanitation is critical. Since you don't know that the lag period will be long while sanitizing your fermenter, it is critical to make sure that you clean and sanitize your gear well each time you use it. That said, most homebrew beers are contaminatedŁ at some level, the degree of contamination may not be very high but these low level contamination can cause phenolic, estery, lactic or enteric characters to appear in your final product. Once active fermentation takes over, the risk of these contaminations ruining your beer is low because the environment that fermentation generates is highly unfavorable for other microbes. Pitching an old starter or yeast with poor viability can give off flavors, not from the fermentation by the healthy yeast but from the breakdown of the dead and dying yeast. Often a vegetal character is described in this situation.
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