Microbiology of Beer, Bread and Cheese – Fall 2017

Laboratory 1: Chemical Analysis of Beer

Introduction:

Many changes happen to the raw components of beer (in our kit the components were Amber Malt Extract, Light Dried Malt Extract, Hop Pellets, Munton’s or Brewpub ale yeast and water) throughout the brewing process. We will be studying only a few of those changes. Specifically, we will analyze the specific gravity, color, and bitterness, and will use those measurements to learn more about the chemical composition and taste of the final product. We will also study both types of yeast by making microscope slides and by observing their flocculation behavior.

The information below comes in large part from the Homebrew Digest article by Peter Ensminger at The information on beer color and calculating the Loviband Scale comes from. Finally, the information on how to determine the level of acidity in beer is from.

Test 1. Specific Gravity, Alcohol and Sugar

We will be measuring the beer’s specific gravity (SG) using a hydrometer. Specific gravity (g/ml) is beer’s density with respect to water. Wort has a relatively high sugar content, and will thus have a higher specific gravity than water (1.00 g/ml at 20°C). Beer, on the other hand, will have a lower specific gravity due to the increase in alcohol (Ethanol has a density of 0.79 g/ml at 20 °C). The difference between the specific gravity of the wort (original gravity, or OG) and the specific gravity of the beer (final gravity, or FG) can thus be used to calculate a variety of final beer characteristics.

  1. Alcohol By Volume (ABV %)

ABV = (OG - FG) x 131.25

Brewpub yeast values: OG 1.050, FG 1.020

Kit yeast values: OG 1.050, FG 1.018

  1. Plato Scale (°P) measures the sugar levels in beer. Since the specific gravity of wort will go down as sugar is converted into ethanol, the specific gravity can also be used to estimate the amount of sugar in the product. 1° Plato is equivalent to 1% sucrose (1 g sucrose/100 g beer).

°P = (-463.37) + (668.72 × SG) - (205.35 × SG2)

Example: The specific gravity of a wort is 1.070 and that of the resulting beer is 1.015 at 20 °C. What are the densities on the Plato scale?

According to the equation:

°P[initial] = °Pi = (-463.37) + (668.72 × 1.070) - (205.35 × 1.0702) = 17.06

°P[final] = °Pf = (-463.37) + (668.72 × 1.015) - (205.35 × 1.0152) = 3.82

  1. Real Extract

Real extract is a measurement of the sugars that are fermented during the brewing process. It is calculated using the initial and final densities of the wort in °P.

RE = (0.1808 × °Pi) + (0.8192 × °Pf)

  1. Attenuation

Attenuation, plain and simple, is the amount of sugar that has been fermented to alcohol. Some yeast strains can convert more sugar than others. As with the other measurements we have made thus far, hydrometer measurements before and after fermentation are used to measure attenuation. Unfortunately, using specific gravity is an imperfect measurement because while all of the sugars are dissolved in water in the original wort, some of the residual sugars will be dissolved in ethanol in the beer (not just in the remaining water). Thus, many brewers use the term “Apparent Attenuation” (AA) instead.

AA = 1 - [°Pf / °Pi]

The "Real Attenuation" (RA) can be calculated from the RE (see eq. 2) and the initial density, °Pi:

RA = 1 - [RE / °Pi]

  1. Calories

Calories in beer all come from alcohol and residual carbohydrates (no fat or cholesterol!), and can be calculated as:

cal per 12 oz beer = [(6.9 × ABW) + 4.0 × (RE - 0.1)] × FG × 3.55

Test 2: Beer Color

We set out to make an Amber Beer. Let’s see how we did!

Beer color originates largely with the color of the malt that is used. Remember that after the barley (or other grain) is malted, it is dried and then roasted, toasted, or sometimes even smoked! As we learned in class, this heating causes carmelization and the Maillard reaction to occur, and these reactions cause the formation of dark colors and strong flavors and aromas. The longer a grain is roasted (or the higher the roasting temperature), the more it develops these darker colors and stronger flavors. Ultimately, roasting the grains influences the final color, flavor, mouth feel, body, and aroma of the final beer product. Thus, you can often tell quite a bit about the beer you are going to drink just by looking at its color.

1. Measuring Beer Color:

EBC

The European Brewing Convention (EBC) has created a method to quantify beer color, based on the beer’s absorbanceat 430nm (A430), using a 1cmpath length. For EBC values, the absorbance is then multiplied by 25.

Degrees Loviband (°L)

The American Society of Brewing Chemists quantifies beer color using the Standard Reference Method (SRM). This method measures the absorbance of beer at 430 nm using a ½” path length. The SRM value often uses the units Degrees Loviband (°L).

Since we have 1 cm cuvettes (not ½”), we will be measuring EBC. To convert between EBC and °L, simply use the following formula:SRM = EBC/1.97

Test 3. Beer Bitterness

To estimate beer bitterness, you need to know the original alpha acid content of the hops you added, the amount of hops you added and the amount of time you boiled the hops. A bitterness calculator can be found at:

Test 4. Microbiology of Beer

  1. Yeast Flocculation:
  2. The yeast cells have been sitting undisturbed since Friday. Observe the test tubes for both yeast strains. Have all of the yeast flocculated, or do some remain in the beer (the beer will be cloudy)?
  3. Now shake the 50 mL tubes vigorously for 30 seconds. Observe the yeast cells immediately. Did they separate completely, or are they still somewhat clumped together? Which strain is the most clumped?
  1. Yeast Appearance:
  2. Take 1 mL of the resuspended yeast cells, and place it in a 1.5 mL microcentrifuge tube. Spin 10,000 rpm for 1 minute. Decant the liquid and resuspend the cells in 1 mL of water. Repeat.
  3. Place 1 loopful of yeast cells on a slide and spread over 1/3 of slide. Let air-dry, then heat fix.
  4. Flood the slide with Crystal Violet for 30 seconds, then rinse with plenty of water and blot dry with bibulous paper. Observe using the high dry (40X) objective. Draw the yeast.