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The Theory of Osmolality and Freezing Point Measurement

Osmolality (or Osmosis) is a term used to define the force of attraction between two substances due to their different solubility in water or other liquids. Osmolality is defined as the concentration of one substance relative to another. For example, if a solution contains 100% salt, then it will have a higher osmotic pressure than pure water. If a solution contains 50% salt, then it will have a lower osmotic pressure than pure water. Osmolality is measured in units called millimoles per liter (mM/L). One mole of any substance (in this case, salt) contains 602,370 millimoles. Another way to think about osmolality is by ratio. For a 1:1 ratio of salt, each liter of solution would contain 602,370 millimoles of salt. Osmolality of human blood is between 270-300mOsm/L.

It is a type of colligative property which measures the effect of non-soluble particles in solution such as, Polyphenols (which is responsible for the bitterness of tea) and sugars. Unlike other colligative properties,Raising the temperature will decrease osmolarity.

For example, if you place table sugar in water, nothing really happens to the solution. That’s because table sugar is already soluble in water. If you place a spoon of cornstarch in the solution however, the solution will thicken as the cornstarch dissolves into the water. A general rule is, as a substance is soluble in water, it lowers the solution’s osmolarity. However, if the substance isn’t soluble in water, it will increase osmolarity. Commonly, the more soluble a substance is in water, the lower its freezing point.

The freezing point of a solution is the temperature at which the solution becomes solid. The freezing point of pure water is 0 degrees Celsius (32 degrees Fahrenheit).

The freezing point depression of a solution is the difference between its freezing point and that of pure water. For example, If you place 1kg of pure water in an insulated container at 0 degrees Celsius and seal it tightly, it will stay liquid as the outside environment is also at 0 degrees. However, if you place 1kg of pure water in a container at 0 degrees and open it to the outside environment which is at -10 degrees, it will instantly become solid (or freeze) as the freezing point of the solution has now dropped to -10 degrees. This is due the added solutes (or particles) in the solution causing the freezing point of the solution to be lower than that of pure water.

Raising the temperature of a solution will not increase its osmolarity. However, raising the temperature of the solvent (or in this case, water) will increase its osmolarity.

This is why you should never drink water that is hot as your body cannot handle the high osmolarity of the solution and can lead to serious burns in the mouth, esophagus and stomach if not instantly vomit forth.

Polyphenols have a negative impact on beer flavor. For this reason, most brewers want to remove them from the wort before boiling.

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There are two methods of doing this using either chemical or physical means.

Chlorine is a common water purification chemical used to kill bacteria in drinking water. It works by combining with electrons from the bacteria and destroying it (a process called oxidation).

It can also be used to oxidize out polyphenols from brewing water. In order to do so, you must first add a chlorine compound (such as sodium hypochlorite or calcium hypochlorite) to the water before adding the malt. The compound is then rinsed with the brewing water and polyphenols are oxidized out.

Physical means involve using a solid material such as activated carbon to bind the polyphenols from the water.

Once the wort has been boiled with hops, it is now ready to be cooled down and yeast is added to initiate fermentation.

Viscosity

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Viscosity is a matter of how thick or thin a liquid is.

Thicker than water? Such as honey or molasses? Thin like water? Or in between?

Viscosity is measured using a unit called a poiseuille, after Henri Poiseuille, a french physician who studied the movement of liquids.

Generally, as a liquid becomes hotter, it also becomes thinner (have you ever noticed water seems to spill more easily from a hot pan?

). This is because as heat is added, the average velocity of the molecules is higher.

Polyphenols have a direct impact on the viscosity of beer. Since they are an aggregate, they are not as easily dissolved by the alcohol and begin to settle out as sediment at the bottom of the bottle or during secondary fermentation.

The final taste of beer is generally accepted to be more bitter than any other taste. This is due to the interaction of the polyphenols with the taster’s taste receptors.

The presence of tannins in a beer will generally cause it to be more astringent to the taste. This is generally considered a negative to most beer drinkers.

Alcohol has a very interesting interaction with all of the compounds found in beer. Alcohol is a very polar molecule and is easily dissolved by polar solvents (such as water).

In fact, this is how it causes people to get drunk. The alcohol is able to pass through the stomach wall and enter directly into the blood. Once in the blood, it prevents acetylcholine from binding to the muscarinic acetylcholine receptor. Acetylcholine is a neurotransmitter which causes the brain to be less in control of skeletal muscle movements. This causes slurred speech, dizziness, and other common effects of alcohol.

Alcohol will also have an effect on the acidity of the stomach. Normally the stomach produces hydrochloric acid to help with the digestion of proteins.

However, in the presence of alcohol, the stomach will not produce this acid and the ability to digest food is greatly reduced. This is why drinking on an empty stomach is never a good idea!

The third and final way that alcohol affects the body is by becoming a new chemical host for other compounds. This is accomplished by the addition of a hydroxyl (-OH) group.

This process is called oxidation. The liver can only metabolize a limited amount of alcohol per hour, which is generally why people get drunk (and eventually sick) once they’ve reached their limit.

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Even though there are many different kinds of alcohol found in beer, ethanol is the only one that causes a person to get drunk.

Beer is generally grouped into two main categories, ales and lagers. This is dependent on the genus of yeast used during primary fermentation.

During primary fermentation, the yeast will multiply until there is no more sugar for it to consume. This medium-weight alcohol is what generally causes a person to get drunk.

The yeast used during the primary fermentation of an ale will generally multiply quickly, and then gradually taper off once the sugar is depleted. This generally results in a sweeter tasting beer.

The yeast used during the primary fermentation of a lager will generally multiply slowly, and continue to multiply long after the sugar is depleted (as opposed to tapering off). Since these yeasts are working overtime, they tend to leave more compounds behind than their ale counterparts.

This generally results in a less sweet beer.

Porters and Stouts are generally either categorized as ales or lagers, however the alcohol content is generally higher than average.

Barley wines are generally lagers and have an even higher alcohol content, generally ranging from 7-12% ABV.

Amber beers are generally ales and tend to have a light caramel flavor due to the malt being heated at a low temperature in the brewing process.

The alcohol content of these beers generally range from 4-6% ABV.

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Pale Lagers are generally light in color and flavor.

These beers generally range from 4-5% ABV.

The alcohol content in a given beer can be altered by selecting different kinds of malt and the length of time spent fermenting.

The process of fermenting beers has been around since ancient times. Back then, the procedure was generally less refined than it is today.

In these days, brewers didn’t really have a scientific understanding of why their brews turned out the way that they did.

This is where a little educated guessing came into play. If a batch of beer came out a bit on the cloudy side, they guessed that maybe they left the fruit used to flavor the beer in a little longer.

If a batch of beer was a little bit on the flat side, they guessed that maybe they hadn’t boiled the wort for quite long enough.

As time went on, these guesses eventually turned into established procedures. One thing led to another and here we are today!

The process of brewing beer is relatively quite simple in theory.

Once you have your grain, you steep it in water (called “mashing”). This converts the starchy grain into sugar.

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You then drain the watery sugar water into a large trough called a “cooler.” Once in the cooler, you add yeast to kick off the fermentation process.

Once the yeast starts working its magic, the liquid (known as wort) is then boiled to sterilize it and to add flavor (hop pellets). After this, the wort is cooled and yeast is added once more.

After about a week or two, the beer is ready for packaging.

Up until this point it’s all fairly easy. But here’s where it starts to get more complicated.

Nowadays, craft breweries have gotten quite experimental with their beers and the ingredients that go into them.

Some craft brewers have taken to using fruits, various spices, and even different types of wood in their beers. Some even go as far as to use special kinds of yeast that produce different kinds of alcohol (such as Stout yeast, which results in a beer high in alcohol content).

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In some cases, the process of making these specialty beers can get quite involved.

So that’s a basic overview on how to make beer.

Beer is delicious and fun. So have some!

Return to Brewing page.

Sources & references used in this article:

What is Ross River Fever

Pharmacology