It’s that time of year again … Saint Patrick’s Day. A time for letting loose, having fun, drinking beer! Have you ever stopped to think–how does this rich, black stout keep it’s consistently perfect flavor? How do they always deliver that perfect foam and fizz? The answer? Yeast banking. Visit your favorite Irish beer’s website and you’ll see. Take Guinness for example:

“Next comes the Guinness yeast, a strain that’s been handed down from generations past. It’s so precious that we keep a reserve amount under lock and key, just in case anything should happen to our main supply. The yeast captures the full freshness of every one of the painstakingly sourced ingredients, ensuring our beer is perfectly fermented and charged with the flavor that’s made us famous across the globe.” —Guinness® Brewing

Without yeast banking, that consistently perfect flavor and fizz of your favorite fermented beverage would fall flat in time.

The question is, can you do it at home? Absolutely. Let’s look at how.

What is yeast banking?

A yeast bank is a store of isolated yeast–wild or harvested, that is kept alive for future use. A yeast bank or culture library is an important part of any brewers kit. The same could be said for mushroom growers as well, as spawn and cultures can be stored in similar ways.

Banking methods

There are a few accepted methods in the brewing and culturing world that generally have consistent results. Let’s look at a few:

Agar-agar plates

While agar-agar plates or Petri dishes are great means of cultivating cultures for growth, they are not ideal for long term storage. In time they will dry out and your cultures will die.

Agar Slant

For short term storage–six to nine months–an agar slant can be used. Similar to the agar plates, agar is poured into a tube which can then be sealed off, preventing drying out. This method is ideal for the small-batch home brewer as it can be stored in a refrigerator and accessed with relative ease.

As with all culturing projects, you will require sterility when it comes to your mediums and equipment. This will require you to have access to an autoclave or at least a pressure cooker, which is often more reasonable for the home brewer. You will also need agar-agar, an inoculation loop, and ideally, an agar plate/petri dish streaked with an isolated yeast colony.

Glycerin Freezing

For more long term storage you might want to consider glycerin freezing. While yeast does go dormant in typical refrigerator temperatures, not all metabolic functions stop, which means in time, they will die.

Freezing, on the other hand, is a much longer form of storing, stopping all metabolic functions and allow in the yeast to be stored for a longer period of time. For home brewing purposes you are looking a 1-3 year life, maybe longer due to the warmer temperatures in home freezers. Commercial operations will have the ability to store at much lower temperatures, thus extending the life of the yeast.

This type of storing will require the use of food-grade glycerin, pipettes, and an autoclave, but will harness much better long term results.

From yeast to beer

Beyond using a favored strain of yeast, brewers like Guinness rely on the basics of all brewers of beer: Barley, Hops, water, and a secret recipe is all you need. That combined with a little patience and you can be home brewing in no time.

Of course, it may be too late for you to get started for this year’s holiday celebration, but there is no time like the present to start preparing for Saint Patrick’s Day 2020!