The Cold (and Boring) Side of Brewing

• Post By: Scott
• Date: 01.08.2013
• Category: Articles

We’re always excited about a new recipe we want to try, our next brew day, or a new piece of equipment to brew with. Unfortunately, that same enthusiasm rarely carries over to fermentation, and that’s where the magic happens. Great brewers will tell you: “Good beers are all about fermentation”, “Fermentation, Fermentation, Fermentation”, etc, but despite the importance, it seems to be the least romanticized part of brewing. So I decided to write a post about how I care for my yeast, and what happens after the flame goes off. FYI, a lot of this might be repetitive for some brewers, but I’ve had a number of requests for this topic.

 

The first thing every home brewer should be told is that the brew day isn’t that important. You can commit the brewing equivalent of murder during the the brew day, and if the beer was fermented well, it’ll most likely still be good. Let’s define some terms first. The ‘hot-side’ is wort production; the part of the brew day where you’re making wort. It starts when you mill your grains (or mix in your extract), and ends when you kill the flame on your kettle. The ‘cold-side’ is everything that happens after you turn off the kettle (fermentation, clearing, packaging, etc), and the handling of your yeast. Even though it’s much more fun to add hops to a kettle, great beer is made during the cold-side.

 

Yeast
Yeast make beer. It sounds silly, but wort itself doesn’t taste good. The flavors and compounds that yeast generate are what make beer, beer. So yeast should be your primary focus. The first question every brewer should ask before starting a batch is: “Do I have the proper amount of healthy yeast for this beer?” Now in the case of a 1.035 Bitter, it could be as simple as a single vial or smack pack. For a 1.080 Imperial Stout, we’re going to need a massive starter, multiple vials, or re-pitch yeast from a prior batch. I don’t need to cover pitching rates and cell counts here, as there are a bunch of great calculators available. I use mrmalty.com, and get good results from his numbers. I find his viability percentages to be a bit too conservative, but it’s otherwise spot on. The important thing is to stick with one calculator, try it, find out if it works for you, take notes, and adjust as needed.
Oxygen
Most home brewers oxygenate by some means that introduces atmospheric air into wort. Most home brewers (myself included) don’t get enough oxygen saturated into their wort. It takes a lot of shaking, with a decent amount of head space to get 8ppm of O2. I finally broke down and bought an O2 regulator and stainless diffuser stone so I can aerate with pure O2. I noticed an immediate difference on high gravity beers, and batches where I re-pitched yeast. If you don’t brew high-gravity beers or re-pitch yeast, you might not see the benefit. I, personally, will never go back.
Temperature
People are unhappy when they are too cold or too hot; yeast are no different. Steady, controlled temperatures are very important to clean fermentation. A sizable chunk of yeasts’ ester production occurs during the growth phase of fermentation. That happens to be the first 12-72 hours or so. For this reason, I am a proponent of pitching my yeast into wort that’s a few degrees colder than my target fermentation temperature. This allows the yeast to slowly acclimatize to the environment, and ensures they won’t take off like gangbusters. Lag time isn’t something you should fear, assuming that you sanitize properly and pitch a proper amount of healthy yeast.

 

Now that the yeast have acclimatized, started to multiply, and warmed up the wort to my target fermentation temperature, my goal is to keep that temperature consistent. Firstly, ambient temperatures do not equate to fermentation temperatures. Buy some of those cheap little liquid crystal stick-on thermometers for like $1-2. They are surprisingly accurate, and will show you what the temperature of your wort is. There was BYO article a few years back that showed the temperature of fermenting wort in the center of the fermenter was no more than .5F off from the temperature sticker stuck to the outside (Do keep in mind we’re talking about 5 gallon buckets and carboys.) For the skeptics, a sanitized probe thermometer will also work.

 

There are a number of methods to keep a fermenter cool. Swamp cooler setups, frozen water bottles, refrigeration, or just a cool basement all work. I live in Arizona, so it didn’t take me long to opt for refrigeration and a temperature controller. I tape my temp probe to the side of the fermenter; it works well. Whatever method you choose, just make sure that your temps are reasonably steady. 1-2* of swing isn’t too bad, but I’d work to keep it from swinging any more.

 

Fermentation will reach a noticeable peak, and then activity will start to slow down. Every stain is unique, but generally, allowing the fermenter to slowly warm up at this point is good idea. I ferment most of my ales around 62-66*, but at this stage, I’ll let them free rise to 68-72. The yeast will take up and metabolize diacytl, as well as a host of other compounds that could lead to off flavors later on. Keeping the yeast warm and happy at this stage will also aid the yeast in entering their dormant stage. They’ll floc better, and generally be healthier for re-pitching.

 

Re-pitching Yeast
Don’t re-pitch yeast from a prior batch if you weren’t completely clean and sanitary throughout the process, or if anything about the fermentation seemed off in any way. Since I typically only re-pitch for a couple generations, and don’t store my yeast for more than a couple days, I don’t bother to separate the trub from the yeast. Using a thoroughly sanitized ladle, I mix up the slurry at the bottom of the fermenter, scoop up a measured amount, and directly re-pitch to the next batch.

 

Don’t pitch onto an entire yeast cake; it’s bad practice. You’re almost always over-pitching, and you should be fermenting in a clean, sanitized fermenter. It’s not that hard to measure out a specific volume of slurry; take the time to do it right. Also, yeast nutrients and oxygenation become increasing important with re-pitched yeast. Wyeast, Fermentis, White Labs, etc all grow their yeast in nutrient rich environments. They are healthy and ready to rock out the smack pack, satchel, or vial. Re-pitched yeast is not as healthy and ready to rock, so a healthy dose of O2 and some nutrients go a long way to a healthy fermentation.
Maturation and Packaging
I don’t need to go into depth here, but there’s a few things worth covering. First, I’m not a fan of the month-long primary. I just don’t feel it does anything. It is a good idea to leave the beer on the yeast for a couple days after fermentation has ceased, but the yeast aren’t contributing anything after that. The beer is maturing, which is a good thing, but it can mature off the yeast just as well as it can on the yeast.

 

At this point, your beer is fragile. It’s vulnerable to sunlight, bacteria, and oxygen, so take care of it. Clean and sanitize your kegs or bottles well, and do everything possible to avoid oxygenating the beer at this stage. Those that keg might try flushing their kegs with Co2 prior to racking, especially for hoppy beers. Brewers that bottle shouldn’t be as concerned, as the yeast will take up most, if not all, O2 in the bottle when they ferment the priming sugar. Also, don’t keg or bottle in direct sunlight, as hoppy beers skunk very quickly in direct sunlight.

 

Wrap Up
As with every part of brewing, take detailed notes. Note how the fermentation is progressing, what’s happening with the temperature, and anytime you change something. The more you work with a specific yeast strain, the more familiar with it you’ll become. Every strain behaves a bit differently, and there’s no substitute for experience with a strain. WLP007 for example will attenuate 2-5 gravity points after all signs of activity have stopped. Every yeast has it owns quirks, and detailed notes will help you better understand the yeasts you use most often.

 

I know most of my points in this post aren’t earth-shattering, but the take-away should be to really sweat the small stuff when it comes to the cold-side of brewing. Minor and even major mistakes made during the hot-side portion of the brew day can be washed away with a solid, clean fermentation.