Simple Brewing Science : Basic Molecular Components

2015 is in full swing and it’s time for a post (finally)! I’ve got a couple of brews in the fermentation chamber that I can’t wait to tell you about, but they need a bit more time before bottling. I’d like to be able to present beverages from grain to glass in a single post because I find multiple posts about the same beer to be a bit dull. So while we’re waiting on that to run it’s course, I’d like to introduce a new series Simple Brewing Science! I see there’s a lot of practical homebrewing knowledge out there and many scholarly publications regarding brewing and food science, but not a whole lot to bridge one to the other. I want to help homebrewers improve their scientific vocabulary and understanding. I think that’ll help everyone down the line and it’ll allow me to better explain some of the things I have planned for later in the year. So let’s get started!

Chemistry

Stop! I see what you’re doing there. You saw the word chemistry and you got scared. Your palms started to sweat and you flashed back to high school for a minute. Stop trying to click over to HomeBrewDad or Brulosophy for a minute and calm down. Chemistry is our friend and if you want to understand brewing better, you’re going to have to understand the language of chemistry. Don’t worry, you don’t have to know anything because we’ll start at the beginning (I hear it’s a very good place to start). Chemistry is the study of the structure, properties, and changes in matter. It’s like playing with Legos … extremely tiny Legos. Each Lego in our example represents an atom of some element. When you snap Legos together to build something, you’re making a compound (the Lego structure) using chemical bonds (the snaps holding the Legos together). By and large, the chemistry you’re going to be dealing with in brewing involves taking larger structures and breaking them down into smaller ones. Let’s talk about the major structure types that you’ll be running into as a brewer.

Carbohydrates

One of the most important chemical structures in brewing is the carbohydrate which is sometimes called a saccharide. Carbohydrates are important because they provide the primary source of energy for all living things. They can also provide building structure for plants and animals, help move energy around, and are one of the fundamental components of DNA and RNA! Carbohydrates are awesome! But what are they? Scientists are not very creative people. When they say “carbohydrates” they literally mean “hydrates of carbon” or more plainly water and carbon.

We can generally write this as Cm (H2O) n . It’s generally accepted that m and n are 3 or more. The most basic carbohydrate you’ll see is a monosaccharide (one sugar). Some monosaccharides you might already be familiar with are glucose, fructose, and galactose. They’re all just short chains of carbons and waters arranged in various ways. The number of carbons present are one of the factors determining which kind of sugar it is. Generally, they look like this

The number of carbon atoms helps determine what kind of monosaccharide we’re dealing with. At the end, you have a carbonyl group. That’s nothing more than a carbon double bonded to an oxygen. What comes after this also helps to define what kind of monosaccharide this is. Sometimes you get to the carbonyl and it ends with just a hydrogen attached. This is called an aldehyde. You know when you’re putting together Ikea furniture and you get to the end there’s only that one piece left and everything fits well? That’s like an aldehyde.

However, sometimes you get to the end and there isn’t just a hydrogen, there’s something else. Sometimes, a lot of something else. This is a ketone. Going back to Ikea, this is probably like most of your attempts to put together their stuff; you end up with a bunch of random bits and you glob them on all on at the end in a desperate attempt to be done with it.

While I won’t go into great detail why this structure is important yet, ketones and aldehydes are probably words you’ve heard if you’ve been brewing for a while. This is what we’re talking about about when you hear those words.

So, we’ve talked about the number of carbons and the carbonyl structure to describe monosaccharides, the last thing used to describe monosaccharides are how all the pieces fit together. You can have all the same pieces and put them together differently and end up with different compounds. Let’s look at two monosaccharides you know, fructose and glucose.

The chemical formula for both are C6H12O6, but as you can see, they look different. One is an aldehyde and one is a ketone. When you have two molecules with the same chemical formula put together differently, they’re call isomers of one another. Fructose and glucose are structural isomers of one another since the structure of the molecule is different.

There also comes the case where two molecules may be structurally alike, but mirror images of one another. This is known as chirality. You’ll hear chemists describe a molecule as “left-handed” or “right handed” to describe it’s chirality or which side of the mirror it’s on. The system for determining this is a little beyond the scope of this primer and probably not necessary for most brewers to know, but it is important to point out that in almost every case, only one of the mirror images occurs naturally. This will become important later as the enantiomer molecule (the other side of the mirror image) is something we need for certain brewing reactions.

So once you know that, you know a whole lot about carbohydrates. Other carbohydrates you’ll encounter are just many monosaccharides stuck together. If two monosaccharides are stuck together, it’s a disaccharide. Some disaccharides you know from brewing are maltose (two glucose molecules), sucrose (fructose + glucose), and lactose (galactose + glucose). If many monosaccharides are stuck together, they’re polysaccharides. Some polysaccharides we talk about in brewing are starches and dextrins.

Proteins & Enzymes

What if I told you that the second most important molecule in brewing are actually like tiny machines that are responsible for almost every reaction in living things? They can act as molecular transporters, construction or demolition crews, or even act as messengers.

These molecules are proteins. Like carbohydrates, proteins are complex structures comprising of smaller subelements. The highest level of structure is the quaternary structure. This describes how multiple strands of proteins called polypeptides intertwine and interact with one another, much like a giant ball of worms.

Further down is the tertiary structure of proteins. Tertiary structure describes the three dimensional structure of a single polypeptide chain. This is where we start to see how a chain folds onto itself and that in turn reveals some of its possible function. The hollows left in this folded chain can sometimes form activation sites. When these activation sites form a particular shape and charge areas that can catalyze reactions in other molecules, that protein chain is called an enzyme.

Even further down is the secondary structure. Secondary structure describes how localized groups of amino acids link to each other geometrically. Short descriptions of these individual links are known as peptides. Some of the shapes used to describe link geometry are the helix, the pleated sheet, and turns. These shapes help to determine what “side” of the amino acid might face into or out of an activation site.

The very base structure of the amino acid is the primary structure. The primary structure is literally a list of which amino acid is connected in sequence. An amino acid has 3 main parts; an amino group (NH2), a carboxylic group (COOH), and a “R” side group. The R group is what differentiates amino acids from one another. In the case of our enzyme analogy, the R groups are responsible for the individual active sites, like the teeth of a key. When a molecule comes in contact with an enzyme, the key fits into the molecule’s “lock tumbler” lowering the activation energy of the molecule and allowing a bit of it to be broken off. This is how we go from very long molecules of starch to disaccharides of maltose.

You might also be familiar with the term free amino nitrogen or FAN in brewing. The organic component of FAN is literally the concentration of individual amino acids that are floating around not bound into a protein or only connected in very, very small peptide chains. Just keep in mind that these very basic building blocks are used by yeasts to build up their own proteins for cell division and efficient fermentation.

Lipids

The final molecular component we’ll talk about in beer are lipids. Lipids are a small component of beer, but they help in the health of the yeast (in moderation) and they play a role in mouthfeel, flavor, and head retention of beer. What are they? It’s hard to talk about lipids in a general way because they encompass so many subtypes, but very generally speaking, they’re molecules that are made up of fatty acids (or fatty acid derivatives) and are insoluble in water.

So, that’s cool and all, but what’s a fatty acid? Essentially it’s a long chain of hydrocarbons (hydrogens and carbons) with a carboxylic acid group at the end (a carbon double bonded to a oxygen and bonded to a OH group). This shape results in one end being charged and hydrophilic (water loving) and the other end being neutral and hydrophobic (water avoiding). This is a tricky balancing act because it means that fatty acids can be turned into surfactants (soap) or into water soluble compounds (like bittering in beer!). As you may have guessed, lipids come in molecular forms of various complexity. The complex lipids we see in brewing include triglycerides, waxes, and phospholipids. I won’t bore you too much with what each of these structures look like, but these compounds are primarily important for building yeast cell walls and helping in head retention. Your simple lipids are mostly made up of fatty acid derivatives like isoprene and include things like steroids, prostaglandin, and terpenes. These encompass your hop alpha acids and essential oils, basically the tasty and aromatic components of hops.


So that’s it for the basic molecular components of brewing. Since we know the building blocks we’re starting with, we can now move onto reactions and what’s actually happening from grain to glass in subsequent posts in this series. Let me know what you think about this series by dropping me an email or hitting me up @immaculatebrew if you're on Twitter.