Bare-Bones Basics #5: Yeast

Yeast Cells Under a Microscope

Yeast Cells Under a Microscope

The thing that makes brewing beer work, or, more generally, the thing that makes ethanol in general, is yeast. (Now, you can synthesize ethanol, industrially, through the hydration of ethylene, but this involves using some nasty chemicals that don’t belong in something you plan on drinking.) Yeast, as you probably know, eats sugars in your beer and (as Tim likes to put it) poop out alcohol.

Yeast is a single-cell fungus, which is found just about everywhere. All types of yeast reproduce asexually, though there is a process of genetic material exchange between cells. The yeast species you are probably most familier with is saccharomyces cerevisiae, ale yeast. This is actually the same specie as baking yeast, but in general, brewers use a less aggressive yeast strain that produces fewer unwanted chemicals that would give the beer an undesireable taste. Saccharomyces carlsbergenis, called so because it was first isolated by Carlsberg, also known as saccharomyces pastorianus or lager yeast, is, unshockingly, used in lagers. Saccharomyces carlsbergenis is a combination of saccharomyces cerevisiae and a third type of yeast, used mostly in wine and ciders, saccharomyces bayanus.

The thing most important for your beer that you need to know about the differences in these yeasts is that lager yeast generally has higher attenuation, meaning it can eat more sugars, leaving your beer more dry (though the variation in strains of each lager and ale yeast provides a large overlap), and that it works at a colder temperature (about 10-15 F colder) than ale yeast.

All alcohol-producing yeast can work in two different ways, based on if there is oxygen around or not. When yeast eats sugars without oxygen, the yeast gives off the waste of ethanol, and carbon dioxide, along with some energy. This energy does two things, it powers the yeast cell, so it can grow, and warms the liquid it is in. When there is oxygen present, the yeast cell can completely break down the sugar into water and carbon dioxide. This produces significanly more energy for the yeast cell, which lets it grow much faster.

When you add your yeast to your wort, you want some oxygen to rapidly grow your yeast so fermentation doesn’t take a long time. Once the yeast has consumed all the oxygen in the wort, it then switches to anarobic fermentation (without oxygen) and makes ethanol. If you have a large quantity of yeast cells to start with, you don’t have to oxygenate your wort as much, and you’ll get higher alcohol concentrations (and less water) in your beer.

Another stat you may see on the side of your yeast pack is ‘flocculation’. Flocculation means the ‘clumping’ of yeast cells in your beer. This sounds like it might be a bad thing, but actually it’s good. When your yeast cells are done eating sugars, they can do one of two things: with yeast that has a low flocculation, it will just sit suspended in the beer. High flocculation means the cells will clump together and float to the top, in the case of ale yeast, or sink to the bottom, in the case of lager yeast. This will make your beer clearer. Some beer styles are traditionally cloudy with yeast, and has a slightly different taste because of it.

Some of you may notice I didn’t mention brettanomyces, a genus of yeast used in making lambics. This yeast is naturally found in the air in the southwest of Belgium. Lambics are made, not by adding yeast directly to the wort, but by allowing them open access to the air. The yeast particles in the air fall into the beer, instead of physically putting a yeast solution into the beer. This yeast gives lambics a distinctive sour taste. This open fermentation, you might think, wouldn’t work, because it isn’t separated from the air. If the wort is exposed to the air, it will have access to oxygen, and the yeast would never anaerobicly ferment the sugars into ethanol. However, if you remember part of what is released is carbon dioxide. CO2 is heavier than air and sits on top of the wort, creating a barrier between the oxygen in the air and the wort, allowing fermentation.

White Lab Varieties

White Lab Varieties

There are many different strains of each of these species of yeast. Each have slightly different characteristics that will produce slightly different results. More or less flocculation, more or less attenuation, higher or lower prefered fermentation temperatures, etc. These allow you to fine tune your beer, in a general sense, the important distinguishing factor is ale yeast, lager yeast, or lambic yeast. This hopefully helps you understand how yeast works, and gives you a better idea as to what is happening inside your carboy.

Bare-Bones Basics #4: Grains

Aside from perhaps yeast, grains are arguably the most important aspect of beer. They provide the sugar for fermentation, a great deal of the flavor, enzymes to help the yeast break down difficult-to-digest sugars, and almost solely are responsible for the texture of a beer. In short, grains are to beer as grapes are to wine (suck it, Jim Koch).

The sugars in harvested grains are not readily useable by yeast. They start as starches, which are long strings of sugar molecules in a chain. Yeast can’t work it’s magic on these so they must first be broken up. Fortunately, this can be done by a process called “malting”. Basically, to malt a grain, you let it start to grow (germinate, for the botany-inclined) by soaking it in water. The germination process releases enzymes that break down the starches into sugars. It is then, in a controlled fashion, heated (kilned) to stop the germination. The amount of kilning affects the grain’s flavor and color.

The most common grain used in beer (and the only one allowed in Germany while still called ‘beer’) is barley. Barley used in brewing comes in various strains, each of which are processed in any number of ways, allowing for a wide range of options for ways to change your beer. In a general sense, most barley grains fall into two categories: Two-row and Six-row. Two-row is the traditional barley strain used in most European beers. Six-row is more common in American beers and has been bred to have higher enzyme content that will help break down more complex sugars in adjuncts added to the beer.

Wheat is used often in certain styles of beers (the over-arching category would be aptly named ‘wheat beers’). Germany and Belgium are most known for their various styles of beers featuring wheat. Wheat malts can not be used as 100% of your grain bill as they lack enough of the enzymes needed, and therefore should be used in conjunction with barley. Wheat also adds a noticeable haze to beer.

Other grains, such as oats, rye, even potatoes can be used to add fermentable sugars, too, but are more rare. We’ll try to do a beer and post about these on an individual basis.

Bare-Bones Basics #3: Bottling

Bottled beer has been around since the 1500s. Before that, the only real way to get your beer was straight from the barrel. Now, the most common way for you or I to have a beer at home is for us to buy a six-pack. So, how is beer bottled? What gives it the carbonation? Why are some beers more carbonated than others?

There are two major ways for a bottle of beer to have carbonation in it. The first, and original, way for beer to be carbonated was the beer was to be sealed in bottles before the fermentation was finished. When fermentation occurs, it releases CO2. Airlocks in fermentation tanks release this CO2.If the tank is sealed, the CO2 has nowhere to go, and therefore stays in the liquid. Since bottles are airtight, the it continues to ferment, carbonating the bottle of beer.

However, this is more difficult to do than it sounds, since bottling the beer too early in the fermenting process could easily result in the bottles becoming too carbonated, and burst the bottle. This resulted in a modified method of bottling beers. The modern method is to ‘prime’ the bottles. In non-filtered beers, yeast is still present in the bottles. Therefore, just before bottling, priming sugar mixed with water is added to the fermented beer. This allows for a more controlled amount of sugar to be present in the bottle before it’s fermented inside the bottle.

In modern mass-produced beers, bottling is very different. Since most mass-produced beer is filtered, and therefore, lacks yeast to ferment inside the bottle, the carbonation is more directly added. The bottling company simple adds CO2 inside the bottles and the gas enters the liquid.

Some beers, notably Guinness, and other similar beers, like Tetley’s, use Nitrogen for most of their pressurization. The nitrogen is less soluble than the CO2. This means that the beer can be pressurized higher with less ‘fizzyness’. This is why, when you drink it, nitrogenated beers taste so smooth. The bubbles of nitrogen form very small bubbles compared to CO2, leading to a creamy head.

Bare-Bones Basics #2: Hops

Now, most beer drinkers know that beer has 4 things in it: Water, Grain, Hops, and Yeast. In our first Bare-Bones Basics dealing with one of these, we’re going to talk about the hops.

Hop flowers

Hop flowers

Hops are small green flowers (biologist-types will call them ‘strobiles’) that grow on the humulus, which is a vine-like plant. These flowers are harvested once a year in late summer. Since hops lose their bitterness easily, most often, they are ground up, dried, and frozen, until they are sent off to be put in beer. Often, especially for the homebrewer, the ground up hops are made into small ‘plugs’ or ‘pellets’ as seen below.

Paul holding a small bag of hop pellets.

Paul holding a small bag of hop pellets.

As many people know, hops are what give beer a bitter flavor or aroma. It is, however, not as Boston Beer Company says, where “Hops are to beer like grapes are to wine.” Hops provide no sugars to the wort. In fact, you can make beer without hops at all, though it may be a little sweet and/or bland. Flavor-wise, hops do two things, depending on when you add them to your wort.

When added before you are done boiling your wort, hops will make beer more bitter. Boiling hops releases the alpha acids in the flower. The alpha-acid content of hops is generally what you’ll see listed as the defining characteristic of different kinds of hops. Higher alpha-acid percentage means more bitterness per hop.

Adding the hops later, near the end of the boiling phase of the wort, will add aroma to the beer. Beta-acids are responsible for this effect. Beta-acids are more fragile and will boil away if you add them too soon. These can even be added after the wort is cooling. This is called ‘dry-hopping’.

Now, there are many hops that can be used with either technique, but some hops have stronger alpha-acids, and others have stronger beta-acids. Which hops are used all depends on what the brewer is trying to do.

Now last year, there was a bad crop of hops, which led to the prices increasing significantly. If you noticed your favorite craft brew going up a buck or two per six pack this last year, that’s why.

Bare-Bones Basics #1: How is beer made?

Beer has been made for over 10,000 years, but how? What’s happening in those big vats in the brewery downtown? How is it possible to produce beer in your kitchen? Don’t you need specialized equipment?

Well, first off, the reason beer has been made for 10,000 years is because it’s an incredibly simple process:

  1. The starches in grains (generally barley, but there are many different options that will produce various beers) are ‘mashed’ to turn into a mixture of water and sugars called a ‘wort’.
  2. Usually (but not always), small green flowers called hops are added, adding flavor and aroma. Hops also act as an antibiotic to help in the next phase.
  3. Yeast is added to the wort. Yeast is a fungus that eats sugars, and produces alcohol and carbon dioxide as waste products.
  4. After all the yeast has died, the beer is ready to drink.

Now, obviously you can’t throw a handful of wheat into a vat with yeast and say “beer!,” but that’s the nuts and bolts: Make wort, add yeast, wait.