This week I thought I would write a short article on the importance of healthy yeast, as poor yeast is a major source of off flavors in beer.
Some time ago I was reviewing a Beer Judge Certification Program (BJCP) score sheet, which is widely used to judge beer in formal competitions. I noticed that a large number of the “off-flavors” listed on the left side of the score sheet are yeast related.
In fact, of the 16 off-flavors listed on the score sheet, a total of 9 are directly related to yeast health. These flavors includes beer flaws like acetaldehyde, alcoholic, diacetyl, esters, phenolics, solvents, sour, sulfur and yeasty flavors.
To avoid these off-flavors you need to ensure proper yeast health and conditions throughout fermentation and maturation.
Start with Enough Healthy Yeast Cells
The first step is to make sure you pitch enough healthy yeast cells into your wort up front. Beer generally requires a much higher yeast cell count than beverages like wine or mead. There are three main factors driving how much yeast to use: The age/viability of your yeast, the size and gravity of the beer and the size of your yeast starter.
Consider first the age and condition of the yeast you are using. While dry yeast can safely be stored at room temperature for two years or more, liquid yeast is much more fragile with many packages falling below 50% viability within 6 months of packaging. Typical liquid yeast packages have about 100 billion cells when packaged, but most beers require a higher pitch rate, so a starter is needed for most liquid yeasts. Dry yeasts, being more robust, can often be used by just hydrating.
BeerSmith has a yeast starter calculator built into the recipe builder (and as a separate tool) to help you calculate how many yeast cells are needed. You can also refer to this article which covers basic yeast starters. However it is not unusual for a typical ale to require 150 billion cells for a 5 gal (19 liter) batch. Lagers require almost double the pitch rate of ales, making a starter very important.
If you are working with dry yeast, you can often just purchase a few packets and pitch them. Be sure to properly hydrate your dry yeast first. For liquid yeast, you will often need to create a starter by boiling up some dry malt extract (DME), cooling it and then pitching your yeast into the starter a day or two before you brew your beer. ‘
Aerate Your Wort
Adding oxygen to your wort is very important up front. When you boiled your wort, you also forced a lot of the oxygen out of it, but yeast need oxygen up front during the early growth phase to reproduce.
Here’s an article that covers the details of aeration. Methods include shaking/splashing your wort around, using a small aquarium pump to add oxygen and using an aeration wand with pure oxygen.
Of these methods, my preference is to use an aeration wand with a small tank of disposable oxygen, as pure oxygen is needed to reach the ideal aeration levels for the yeast, and these wands are now relatively cheap to purchase and easy to use.
Maintain Proper Fermentation Temperature
Before you pitch your yeast, you first need to bring the wort down from boiling to an acceptable fermentation temperature. If you pitch your yeast into wort that is too hot or too cold you risk shocking the yeast and killing off a portion of your carefully prepared yeast cells.
There are a wide variety of options for wort chilling. Options include immersion chillers, counter flow chillers, plate chillers and variations of an ice bath. Here is an immersion option, and Chris Graham covered some of these very well in a podcast I did with him. Ideally you want your wort to be within 5 degrees of the starter temperature to avoid shocking the yeast.
Next you need to maintain a good fermentation temperature for the length of fermentation and aging. There are a variety of methods to do this as well. A simple method is to put your fermenter in a cool dry place and wrap it with wet towels. Change the towels every 6-8 hours and the evaporative cooling will keep your fermenter several degrees below room temperature which is ideal for ales.
If you have the money or time you can consider other options including ice baths, fermentation chillers and even temperature control systems for stainless fermenters.
Ideally you would like to be able to raise the temperature a few degrees later in fermentation to allow for a diacetyl rest, and later perform a cold crash to help clear your beer more quickly.
Finally you need to allow adequate time for the beer to mature. A number of important changes happen late in the fermentation process, and proper maturation will result in a beer that tastes better and is more stable in the long run.
Those are my yeast tips for this week. Thanks for joining me on the BeerSmith Home Brewing Blog. Be sure to sign up for my newsletter or my podcast (also on itunes…and youtube) for more great tips on homebrewing.
