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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
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
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
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.
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
altering of the mash schedule to enhance head retaining proteins
The use of
heading agents - additives that enhance head retention
of high alpha hops - which will increase bitterness, but also increas
isohumulones that enhance head retention
the use of household soaps on drinking glasses and homebrew equipment
The use of
a nitrogen and CO2 mix for carbonation and serving
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.
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.
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.
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
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
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