This is a summary of a talk President Ed Marquardt gave at the February 2014 meeting at Madra Rua in North Charleston.
......Most of these are well known but sometimes taken for granted! My big focus in the last year has been on the cold side of fermentation – i.e. everything after the boil. That is where you can make you’re biggest improvements. Big shiny brewstands are nice but you can still make bad beer if your practices after the boil aren't up to snuff.
These 4 things are practives that I have identified as common problems that have come up at homebrew meetings and in my own brewing!
After the boil make sure that anything that ever touches the beer is sanitized! Whether its Iodophor, Star-San or something else make sure your fermenters, racking canes, spoons, etc... are free from anything that can infect your beer.
Even after years of brewing I still run into some problems with sanitation. I recently had a batch of Irish Stout get infected because I didn't sanitize some Cocoa Nibs that I had used to add some chocolate flavor. I've also had bottles not sanitized well enough and had infections in the bottles that cause nasty off flavors and overcarbonation, including a bottle explode at a friends house – no one was hurt thankfully. Be sure and safe by making certain your equipment is sanitized.
Pitching and fermenting at the right temperatures is absolutely critical for yeast to produce the flavors that they are chosen for. Fermenting too hot is one of the most common ways to generate all kinds of all flavors (diacetal, acetalaldehyde,phenols, esters...). I always recommend chilling and then pitching at several degrees below your chosen fermentation temperature. If I want to ferment at 62F then I aim to chill the beer to 60F and then put the fermenter in my temperature chamber at 62F.
I use a small chest freezer with a temperature controller as a fermentation chamber. But for years I used the swamp cooler method. By setting the fermenter in a large tub of water (big blue one from Lowe’s!), covering with a blanket, and rotating ice packs in the water a couple of times a day you can keep the temperature of the fermenting beer in a favorable temperature range. For ales this is close to 65F. I always aim a little lower due to the heat generated during fermentation. An easy substitute for ice packs are frozen water bottles.
Most of the flavors are generated in the first 3-4 days for ales. Maintaining the temperature for that initial time period is the most critical! After that its much less important, I often let the temperature free rise to ambient after 4 days when using a swamp cooler and don't notice any off flavors. For chilling the beer down to pitching temperature wort chillers are a necessity! If you have a pump available it helps even more. My procedure is to chill as far down as possible with my immersion chiller and then pump ice water through the chiller to get it the rest of the way. I always have a bag of ice or two on hand!
3) Yeast Pitching Rate
Pitching the right amount of yeast is a surefire way to avoid the off flavors I mentioned above (diacetal, acetalaldehyde, phenols, esters...). There are many calculators out there that give recommendations on pitching rate. Its best to be ±20% of the recommended amount.
If beer is under pitched, the yeast get stressed and do not produce the flavors they are suppose to. Off flavors to some degree are a natural part of the yeast cycle. If there is enough yeast the off flavors that are generated during growth will be cleaned up by the yeast later in the process. But when yeast are stressed they produce significantly more off flavors and then there is not enough yeast to clean those off flavors that are present! If beer is over pitched, yeast do not go through a complete growth cycle. This results in few new yeast cells and an incorrect flavor profile developed due to the proper amount of yeast not going through the cycle they need to generate the right flavors and remove off flavors!
There is another thread on the forum that links to a great article on yeast starters by Jamil Zainasheff. I highly recommend reading it. After years of brewing and reading everything I could find I still learned a few things.
Yeast use oxygen for cell membrane synthesis. Without oxygen, cell growth will be extremely limited. Yeast can only produce sterols and certain unsaturated fatty acids necessary for cell growth in the presence of oxygen.
Inadequate oxygenation will lead to inadequate yeast growth. Inadequate growth can cause poor attenuation, inconsistent or long fermentations, production of undesirable flavor and aroma compounds (mentioned above!), and produces yeast that are not fit for harvesting and re-pitching. For low gravity ales (under 1.050 OG) the amount needed is about 10ppm, for lagers 1.5x to 2x more is recommended.
There are a lot of ways to get that oxygen into the wort. You can shake the fermenter to drive air in or use an aquarium pump with an air stone. The most oxygen you can drive in with either method is 8 ppm - that is the solubility limit using air. To achieve higher than that pure oxygen is needed. Over-oxygenation is generally not a concern as the yeast will use all available oxygen within 3 to 9 hours of pitching and oxygen will come out of solution during that time as well. Under-oxygenation is a much bigger concern – once again the off flavors mentioned above can rear their ugly heads. Most people I’ve talked to have seen an improvement in their beer when they start using pure oxygen to oxygenate the beer. The yeast finish fermentation faster, produce less off flavors, and attenuate better.
For high gravity beers its recommended to give the wort a second shot of oxygen after 6-12 hours of pitching. This gives the yeast another growth boost and helps to ensure healthy yeast throughout the fermentation process. I typically do this on beers with a gravity over 1.090. I wouldn't recommend doing this past 24 hours of pitching due to the interruption in the yeast cycle and the potential for oxygen to remain in the beer can cause cardboard/sherry-like flavors due to oxidation.