Boondocks Brewing
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Refractometer

Refractometers are widely used in the wine and beer industry by to track fermentation, but less commonly used by home brewers.  However, if used properly a refractometer can be a great tool to track specific gravity in place of or to supplement your hydrometer.  This week, I take a look at refractometers, how they work and how an average home brewer can use one.  I'm going to use BeerSmith as the refractometer conversion tool, as the hand calculations are fairly complex and could occupy another entire article.


How a Refractometer Works

A refractometer is an optical device that, like a hydrometer, measures the specific gravity of your beer or wort.  It does so by sampling a small amount of liquid, and looking at its optically.  The main advantage over a hydrometer is the small sample size needed - typically only a few drops.


If you start with a glass of clear water, you will notice that the water and glass bend the light passing through it in a certain way.  The bending of the light by the water is called refraction.  Light bends to different degrees as it passes through different substances.  This is the same effect that glasses lenses in eyeglasses are based upon - the lenses bend the light allowing glasses to adjust the focus of an image and make it clearer to your eyes.


If you add sugar to your glass of water, the light will bend more.  The refractometer takes advantage of this effect to measure the amount of bending (refraction) which indicates the amount of sugar in the sample.  Most refractometers use a prism and a light source to illuminate the sample.  On inexpensive refractometers, you hold the instrument up to a natural light source.  More expensive models have internal light sources.


Most brewing refractometers measure samples in Brix, which is a scale used to measure specific gravity primarily by wine makers.  Some also use a Refractive Index (RI) scale.  Both the Brix and RI indexes need to be converted to standard specific gravity or Plato scales using a formula, as wort does not have the same reflective properties as plain sugar water.


Calibrating Your Refractometer

Before you use a refractometer, it needs to be calibrated.  Most refractometers are calibrated by using a sample of distilled water.  You lift up the daylight (sample plate), and add a few drops of distilled water.  Close the daylight plate and allow the water to spread across the sample plate.  Make sure there are no bubbles.  Refractometers are temperature sensitive, so allow the sample to reach room temperature unless you have a model that automatically compensates for temperature.


Hold the refractometer up to natural light and take a reading.  Most refractometers have a calibration knob or screw that will let you adjust the zero setting.  What you want to do now is adjust the refractometer so it reads zero with distilled water in it.  This may take a few tries.  If you can't zero it out or it is not adjustable, you can handle the adjustment using BeerSmith (see the calibration items under the refractometer tool).


If you want an accurate reading, you should also calibrate the refractometer using a wort sample that has a known specific gravity.  You can do this calibration by mixing up a small amount of dry malt extract with water, then take an accurate hydrometer reading and also refractometer reading and enter both readings into the BeerSmith refractometer tool (use the "calibrate refractometer settings" button).


Using Your Refractometer when Beer Brewing

Using the refractometer is very similar to what you just did when calibrating it.  Open the sample plate, make sure it is clean and dry, then add a few drops of your wort.  Again, if the wort is hot allow it to cool to room temperature first (ideally 68F).  Close the sample plate, check for bubbles, and then hold the refractometer up to a natural light source.


Reading the refractometer is easy - just take the reading directly from the sight scale.  The reading you take will most likely be in percent/degrees Brix or RI.

Refractometer Limitations when Brewing Beer

 

Here's where some people get disappointed when using a refractometer.  Refractometers are calibrated to measure the amount of sugar (sucrose) in a clear sample of water.  The sugar in barley beer (maltose) is a different animal.  Therefore some adjustment needs to be made to take into account the fact that we're measuring colored maltose and not clear sucrose.  You can't just use the measurement you made with the refractometer.


Converting the Brix measurement to a specific gravity or Plato measurement made on a sample of unfermented wort is a moderately complex calculation which requires a spreadsheet or a tool like BeerSmith.  However, there is yet another complication: once the wort starts fermenting alcohol is produced, and the alcohol changes the overall equation yet again.


In practice, this means that in order to calculate the true gravity of a fermenting or fully fermented beer, you need not only the current refractometer reading, but also the starting gravity.  So if you are using a refractometer, it is critically important you record the starting gravity of the wort before fermentation if you want to calculate a mid-fermentation or final gravity for your beer.


Converting  Brix to Specific Gravity or Plato with BeerSmith

Now that we've calibrated your refractometer, and understand the limitation, open up the Refractometer tool in BeerSmith.  Assuming this is your original gravity reading for unfermented wort, select the "Unfermented Wort Gravity" calculation at the top and enter your Brix (or RI) reading from the refractometer.   The "corrected gravity" will show your original gravity for the beer.


Once you have your original gravity and the wort is fermenting, you can take additional readings.  In this case use the "Fermenting Wort Gravity" calculation in the tool and enter both your Brix refractometer reading and the original gravity.  The corrected gravity will show your current adjusted reading.

There is a third calculation in BeerSmith, called "Finished Beer ABV/OG" which lets you back out the original gravity of the beer if you forgot to measure it in the first place.  In this case you need to take a final gravity measurement with both the refractometer and an accurate hydrometer, and enter those readings to get the original gravity.


Are you looking for a refractometer?  MoreBeer carries several great brewing refractometers at great prices.

Thank you again for your continued support!

Brad Smith BeerSmith.com Follow BeerSmith on Twitter and Facebook

Enhancing Beer Head Retention

An important characteristic in homebrewed beers is the ability of the beer to retain a nice foamy head for a long period of time. Commercial brewers go to great lengths to improve head retention by a variety of additives. However homebrewers also have access to ingredients and additives that can help your foam last until the last drop.


Note that enhancing head retention is closely related to enhancing the body of the beer. Foam is the result of CO2 bubbles rising through the beer. These bubbles attach themselves to substances in the beer and form a skin around the bubble. Obviously the more CO2, the more bubbles, but the goal of the brewer is not bubbles but stability of the head. As foam collapeses, evaporating bubbles tend to solidify the beer near the surface, allowing more beer to be poured with less foaming after a few minutes have passed.


Head stability depends on the presence of substances with low surface tension in the beer which can form stable elastic bubbles. The two primary contributors to head retention are certain high molecular weight proteins and isohumulones (alpha acids from hops). Therefore beers with more proteins that are highly hopped will have higher head retention.


Methods for Improving Head Retention

We will explore the following possibilities:

  • The use of body and head enhancing malts such as crystal, wheat, or carafoam
  • The altering of the mash schedule to enhance head retaining proteins
  • The use of heading agents - additives that enhance head retention
  • Addition of high alpha hops - which will increase bitterness, but also increas isohumulones that enhance head retention
  • Limiting the use of household soaps on drinking glasses and homebrew equipment
  • The use of a nitrogen and CO2 mix for carbonation and serving
  • The shape of the glass used to serve the beer

Head Enhancing Malts

The inclusion of proteins and dextrines enhance the body and head retention of finished beer. Unfortunately when used to excess, proteins and dextrines can interact with tannins and reduce clarity and promote cloudiness, so a proper balance must be struck. Crystal malts to include the light Carapils and Carafoam, and caramel malts.


These are the most common body and foam enhancing additives that enhance head retention primarily by adding dextrines and other complex proteins. The overuse of such malts can result in proteins reacting with tannins to create a chill haze. Similarly, other grains high in protein such as flaked barley and wheat can be used to enhance head retention, though again at the cost of clarity.


Mashing Schedule

Since head retention depends on the level of high molecular weight proteins, any step in the mash that breaks down proteins is undesirable. For example, a protein rest in the 50-60 C (122-140 F) range would not be desirable. To improve head retention you would generally favor a full bodied, higher temperature mash, with main conversion in the 158 F (70 C) range, and avoid intermediate protein rests.


Heading Agents

Homebrew shops sell a variety of additives, usually under the generic title heading agent. Some are intended to be added at bottling time, while others need to be added at the end of the boil. Follow the instructions included with the agent to determine what is required. Many heading agents are derived from an enzyme called pepsin that is derived from pork.


Other popular heading agents include iron salts, gums, and alginates. All heading agents will alter the flavor of the beer, in general making the character softer. In general, heading agents are not necessary for homebrews that are made from 100% malted barley and wheat. Heading agents are more commonly used in commercial beers that have high rice and corn content, lacking the necessary proteins of an all-malt beer.


Hops

As mentioned in the introduction, isohumulones which are a form of alpha acid also will enhance the head retention of beer. Alpha acid is the primary bittering agent in hops. Therefore highly hopped beers will have better head retention. Obviously overall malt-bitterness balance is still required, but one can use higher levels of hops, particularly in darker full bodied beers to enhance head retention.


Limit the Use of Household Soaps

Household soaps such as common dish soap and dishwashing soap have a significant detrimental effect on head retention in beer. You should not use household soaps on either your brewing equipment or your main bar drinkware. Detergent washed glasses in particular will quickly reduce the head on even a well constructed beer. Instead use a beer-friendly cleaning agent from your local homebrew supplier.


A Nitrogen Mix

Some beers, most notably Guiness Irish Stout, are carbonated and poured with a mix of nitrogen and carbon dioxide. CO2 is relatively soluable in beer, and therefore does not promote the formation of gas bubbles as well as non-soluable gasses. Nitrogen dissolves less easily in beer, and provides a better base for forming a stable head. However, nitrogen alters the perceived character of the beer, and use of pure nitrogen would result in an unacceptable mouthfeel and carbonation.


A mix, therefore, is always used. The mix varies depending on the style of beer - a low carbonation stout might be served with a mix of 25% carbon dioxide and 75% nitrogen, while ales and lagers might include more CO2 - perhaps 60% CO2 and 40% nitrogen. Low carbon dioxide mixes (25/75) can be applied by mixing the gases in the cylinder, but higher mixes generally require two separate tanks - one of CO2 and one of nitrogen. A high precision blending device either at the tap (i.e. a stout tap) or inline are needed to blend the two gasses for dispensing.


Shape of Serving Glass

The shape of the glass is also a determining factor in both head formation and head retention. A tall narrow glass enhances the formation and retention of the head, while short wide glasses do not. This is the reason many Bavarian wheat beers and Pilsners are served in tall narrow glasses. Use the proper glass for the style of beer you are pouring to enhance the overall presentation.


Thank you again for your continued support!

Brad Smith BeerSmith.com Follow BeerSmith on Twitter and Facebook

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