Lager Yeast Starters & Chill Haze: Mr. Wizard


I always make a yeast starter in order to pitch the proper amount of yeast. Typically, I use a stir plate in the basement, which is a consistent 68 °F (20 °C) ambient temperature. The last time I made a starter I happened to take a temperature reading with an infrared thermometer and it read 80 °F (27 °C). Would this be a problem when making a lager that I plan to ferment at 58 °F (14 °C). Will the yeast mutate at a higher temperature? Should I be concerned about the temperature of the starter during propagation? Should I attempt to make the starter at the planned fermentation temperature?


There is a widely held belief among brewers that yeast should be propagated at, or very close to, the same temperature as the subsequent fermentation. I have always thought that this general rule comes partially from empirical observations and partially from what seems to make sense. If you are getting ready to ride a bicycle race in Colorado, it makes sense to train in the mountains and not at sea level. So if you are preparing lager yeast to ferment at 58 °F (14°C), then it seems logical to propagate the yeast at 58 °F (14 °C) instead of 80 °F (27 °C). The problem I have with this logic is that comparing how an animal responds to environmental conditions is far more complex to how a single-celled organism like yeast responds to environmental conditions. We humans love anthropomorphisms, yet the connections are usually not so obvious.

One of the common misconceptions about lager yeast strains is that these yeasts like the cold and are not as happy when grown at warmer temperatures where ale strains seem so content. That’s three anthropomorphisms in one sentence and the temptation to think of yeast cells as little people is not particularly useful to brewers. The fact is that lager strains grow really well at warmer temperatures and it is also true that the resulting beer is fruitier and ale-like than when the same strain is fermented at cooler temperatures. Anchor Steam is an example of a lager beer fermented at warmer temperatures. The same is true for ale strains; reduce the fermentation temperature and fruitiness usually follows. The main difference is that lager yeasts can ferment at much cooler temperatures than ale strains, and when fermented at the lower end of their functional range, lager strains result in very clean beer.

In my experience, lager yeast can be propagated at warmer temperatures (68-77 °F/20-25°C) and then pitched into cooler wort and be successfully used for lager fermentations in the 50-55 °F (10-13 °C) range. During yeast propagation, brewers are more concerned about growing healthy yeast cells than controlling the environment in such a way to optimize beer flavor. In order to optimize growth the propagating culture is aerated using a variety of methods.

On a small scale, flasks stoppered with cotton plugs and mixed using stir plates or shaker tables have enough gas transfer at the gas-liquid interface to provide oxygen to the growing culture. In larger propagators, air or oxygen is bubbled into the culture and the transfer of oxygen into the liquid is often aided by the use of mixers. In all cases, oxygen is added during fermentation to benefit the growth of yeast. This practice is far different from normal beer fermentations where oxygen is usually detrimental to beer flavor (there are notable exceptions to this rule, such as Yorkshire Square fermenters). My point is that yeast propagation and fermentation methods have some key differences.

You ask about the potential for mutations if lager yeast is grown in a warmer environment. Again, human perception comes into play. Many of us think of a three-eyed fish as a mutation, but mutations are rarely so obvious with yeast cultures. Subtle changes are more common with yeast strains. Cultures may slowly become less flocculent over time, or diacetyl reduction may become problematic, or attenuation may begin to suffer as a culture is used over and over.

Brewers know that changing the environment, for example the fermentation temperature or wort original gravity, is one way to change how a yeast strain behaves. As brewers conduct a fermentation, harvest the yeast from the top or bottom of the fermenter (depending on yeast type and harvest method) after fermentation, re-use the yeast crop and repeat the process, we are selecting cells from the total yeast population for re-use based primarily on flocculation properties. Over time the culture may lose the properties that are desirable to brewers and when this occurs, the yeast is re-propagated from laboratory cultures. This is perhaps the primary reason commercial brewers want to grow the yeast in a similar environment that fermentation takes place. In my view of this subject, I do not believe the nuances of propagation temperature, within the norm of what most of us consider “room temperature,” are likely to have much effect in the typical homebrewery.


I’m new to all-grain brewing. I have a 10-gallon cooler as a mash/lauter tun and get a fair amount of chill haze in my beers. My typical process is two weeks in primary, two in secondary, and two bottle conditioning. I then chill and serve. Is there something I can do to reduce or eliminate the chill haze without a large investment in more brewing equipment?

I am one of those brewers who believe in sticking to the fundamentals of brewing and then bringing in special tools and brewing aids only after knowing that the fundamentals are being addressed. It is really tempting to begin an answer about chill haze with a long discussion about fining agents and how proteins and polyphenols (tannins) can be selectively removed by the proper selection and use of these compounds. You may discover you need to travel down that road and if you do need to use finings to address your chill haze issues you can research this topic at that time.

It is possible to brew bright, stable beer without using finings, but this does not happen by accident. You are new to all-grain brewing, so there are several things that you need to make sure you are doing correctly before you begin looking for a silver bullet to solve the problem.

Here is a short list of items that I would begin reviewing to address your quest for clarity:
1. Malt milling can influence beer clarity if the crush is very fine and you carry an excessive load of particulates into the kettle. Since malt husk contains tannins that react with proteins to form haze, an increase in these compounds from over-milling and poor wort clarity flowing from the lauter tun can cause haze problems in the finished beer. This is one of several reasons that brewers are careful about malt milling and mill gap adjustment.

2. When wort first flows from the lauter tun it is normal for the wort to be cloudy and a bit weak since the lauter tun bottom is normally covered with water prior to filling. For these reasons the wort is recirculated by gently pumping or pouring the “first wort” flowing from the lauter tun to the top of the mash. This flushes the weak wort to the top of the mash and allows the mash bed to establish its filtration properties. The recirculation process in a commercial brewery is typically continued until the wort is clear and the specific gravity has risen to the expected first wort strength. An inconsistent wort flow rate during wort collection can lead to spikes in turbidity so keep the wort flow steady during collection.

3. A vigorous kettle boil for at least 60 minutes is very important for beer flavor and beer clarity since certain undesirable aromas and protein and tannin fractions are removed during the boil. Many brewers add Irish moss, a good source of kappa-carrageenan, to wort towards the end of the boil in an effort to increase the size of protein flocs. Since the large flocs settle faster than the smaller and more fragile chunks of protein “break,” or denatured proteins and protein fragments, Irish moss aids in removing these haze-active proteins from wort and beer. With or without Irish moss, a vigorous boil is a must. Almost all commercial brewers use whirlpool vessels to separate protein break and pelletized hop residues (when pellet hops are used) from wort following the boil. Many homebrewers have begun using whirlpool-type vessels for the same purposes.

4. Rapid wort cooling after the boil is also very important if you want to brew bright beer. When wort is rapidly chilled “cold break” forms and this settles out in the fermenter. Cold break, like hot break, is comprised of proteins and tannins. Cold break formation is hindered by slow wort cooling; this is one reason why wort chillers are so valuable.

5. Cold storage prior to packaging is the closest thing to a silver bullet when it comes to producing clear, stable beer. The reason this method is so effective is that it causes chill haze formation and, given enough time, allows for the haze to settle from the beer. Most chill proofing aids accelerate this process, which is one reason why they are so critical in commercial operations, and do work very well, but at the end of the day are not required if you have time. The important thing about this process is temperature; you want the beer close to freezing, 30 °F (-1 °C) is perfect to cause as much chill haze formation and subsequent settling as possible. You will want to carefully rack your beer off of the sediment before bottling. Since yeast will also settle during this time, it is often a great benefit to add a small amount of yeast prior to bottling.

After you focus on the five fundamentals above, you should see the fruits of your labor. If you still want clearer beer, send us another question and I will discuss finings and enzymes that can be used to combat haze!

Issue: October 2013