Now it's time to explore hop and yeast options. Once we have created the malt color and flavor profile for a specific beer style, it's time to define its place within that style. We do that by our choice of hop variety, quantity, and by the yeast. There is never just one way to appropriately hop and yeast a beer.

Hops: Hops are an extremely complex issue. A single hop choice can define a beer as British or German in style. Beer styles evolved concurrently in many areas of the world. The factor determining which hop varieties were used, and resultant flavor, was largely a pragmatic one... they used what was available. Indigenous hop varieties in the U.K. were not the same as those in Northern or Eastern Europe. Today we have availability of hybrid varieties from all over the world, and active research programs to make new varieties. This was not the case when most of the beer styles we commonly brew were invented. We therefore largely identify a beer's geographic style by the hop types used.

That being the case, we should categorize hops into general geographic styles. For simplicity, we will only mention the most common varieties from any region:

The "Old World" varieties are the original strains from which less traditional hybrids came. Terms like "Noble Varieties" and "Land Race Strains" indicate those original few strains. Recent hybridization programs have yielded remarkable new varieties that exhibit vast differences in flavor qualities and bittering capacity. Having defined basic hop varieties in terms of similarity to familiar beer flavors from around the world, we can hear some of you saying, "why can't anyone just describe hop flavors and aromas in plain simple words!" OK, fine, here is a plain and simple answer. We use things we are familiar with to describe things that are unfamiliar. Hop flavors and aromas are like nothing else, and that makes them virtually impossible to describe. That desire to describe hops gives us supposed attributes such as "spicy", "floral", and "herbal". We know of no one (other than book authors) who claims to actually sense these attributes in hops. That is as close as anyone can come to labeling them. Occasionally a hop's attribute may in fact evoke in your senses some vague recognition of something else, but another person would not likely agree. If you begin thinking about hop flavors being related to identifiable geographic beer flavors, you will become able to define your personal perception of those flavors. It may be beneficial to purchase 2 or 3 similar individual beers from each of these geographical categories, and carefully consider their flavors, thus creating your own "definitions by differentiation."

Yeast: Yeast is no less complex, but we more readily identify it's fermentation impacts and attributes. We are generally familiar with alcohol flavors and ester aromas. We experience them daily in things like ripening fruit and other adult beverages. That familiarity helps us recognize the "fruity" estery designation that some beers have as well as the aroma or flavor of ethanol, similar but mild compared to that in liquor. What we are less familiar with are the subtleties of yeasts. Those flavor characteristics require learned identification, much like hops.

Following are a couple of quantifiable characteristics that help us predict the types of flavors yeast may create: "Attenuation" is the thinning or reducing of sugar concentration during fermentation. As sugars are converted to alcohols and CO2, tangible sweetness of the liquid is reduced and of course, the flavor of alcohol and other yeast byproducts is introduced. Not all of the sugars in malt are fermentable and it is a beer's residual sugar content that helps define its overall character. Of the sugars in an unfermented beer, only 75% to 80% are actually fermentable, or potentially convertible by the yeast. Brewing yeasts have a rather wide range of attenuative potential, ranging from the low 60’s to as high as 80%. Yeast, which can convert only 65% of the total sugars leaves behind quite a bit of otherwise potential fermentables, making the body of the beer fuller, and flavor maltier and sweeter. Yeast that ferments 80% of the total sugars (essentially everything fermentable) pretty much cleans house, and results in a dry, less malty beer, tending to accentuate hoppy qualities in the absence of other sensory stimuli. Choosing yeast by attenuation allows you to shape that important beer quality.

"Flocculation" is the clumping and settling character of yeast. Some strains collect and settle so rapidly they barely stay in suspension until fermentation slows. Flocculation has an impact on some of the alcohols and organics formed in a beer. A "highly flocculent" yeast tends to allow higher concentrations of Diacetyl to remain, commonly perceived as a buttery or butterscotchy quality associated with some beers, most notably Extra Special Bitters (ESBs). Healthy highly flocculent yeasts produce pleasant levels of this flavor. Problematic fermentations may produce excessive concentrations of diacetyl that should not be confused with the desirable character of highly flocculent yeast. Most yeast is more resistant to settling, considered "powdery" or even "non-flocculent.” Generally, these would be thought of as cleaner tasting yeasts, that is, more neutral from a stand-point of the yeast's actual flavor impact. But, there are of course exceptions to this less flocculent/cleaner rule, and yeasts like those used to make Hefeweizens and Wit Beers show how non-flocculent yeast can in fact have a very definitive and critical flavor impact. We are referring specifically to the Clove-like flavor and Banana-like aroma these beers usually carry. (Yes, if you were not aware, those flavors are caused by the yeast!) While desirable in those beers and with those yeasts, those flavors would be considered a defect in a beer not normally associated with that character. Beside the attenuation and flocculation induced flavors, each yeast will have attributes that may subjectively be described by words like "fruity", "malty", tart", minerally" and even "sulfury". Where do these things come from and why don't they show up in all yeasts and beers?

They come from byproducts formed naturally in the fermentation cycle, and they are in fact a part of all yeasts and beers to some degree. What differs from yeast to yeast is how much of what byproduct is produced. Yeasts naturally produce these small quantities of alcohols, organic acids, esters, and sulfur compounds that either:

a) remain below average human sensory threshold
b) or, are removed via the production of CO2, acting as a "scrubber", substantially purging these things from the beer.

That brings us to a brief discussion of palate sensitivity. If most yeasts and beers have some of one or more of the mentioned flavors or aromas, then why can't we always detect it? Or, why do some people detect it more than others? Well, that again is a complex issue, but simplified, it looks like this. Humans have an average sensory range within which most of us can detect flavors or aromas. At the bottom end of that range, some of us will be able to detect and others will not. The point at which we first detect is called the "minimum sensory threshold". From there we continue to sense the flavor or aromatic stimuli more strongly as its source gets more potent, up to a point that we can detect no greater strength. That point is called the "maximum sensory threshold". Between the "minimum" and "maximum" thresholds we sense increasing flavor or aromatic intensity. The same is true with all of our senses. Below a certain temperature, you don't sense warmth, but then begin sensing increasing warmth until it simply feels burning hot. Below a certain level, you don't sense light, and as brightness increases it eventually reaches a point that is blindingly bright. More does not feel any hotter or brighter. In beer and yeast, some people will sense yeast qualities and byproducts sooner and stronger than other people. What one may perceive as the absence of a stimulus is really a matter of sensory level and sensitivity.

While by no means exhaustive or even remotely authoritative on the subject of yeast, one last issue must be addressed. The final topic is propagation and/or re-using yeast. While admittedly a major recipe expense, we DO NOT recommend either of these. It is not because we want more of your money; it is because we do not want you to risk making 5 gallons of vinegar! Propagating, or growing yeast in your home, is very feasible if done properly, but also very risky because the environment is anything but sterile. As you might attempt to make a "starter" to increase the population of your yeast, you would likely be growing a variety of negative wild yeast and bacterial attributes as well. Re-pitching yeast from one batch to another is also very risky. Stray wild things you expose the beer to, prior to the initial fermentation grow in population just as does the desired yeast. Rarely does that relatively small population of wild stuff reach a critical point and make enough negative flavors to ruin a batch in the first usage. The problem arises when the yeast is saved and re-used, and the wild stuff gets a second chance. Generally speaking, undesirable "wild" yeasts and bacteria reproduce at rates faster than the "civilized" yeasts we choose to add to our fermenter. The wild stuff population and byproducts may remain below the threshold of our senses during the first yeast usage, but it is much more likely to reach a critical population quickly in the second usage and make very noticeable negative flavors the second time around. The ultimate question becomes whether it is worth chancing a lost batch in order to save the cost of fresh yeast.

Confused? Well, you're in good company. Few brewers are foolish enough to think they really understand all of this fully. We hope this causes you to think, question, and discuss it more fully with us. With any luck at all, we'll both learn something about a topic that doesn't seem to have a lot of absolute answers.