Fermentation Essentials

Transcription

1 Fermentation Essentials There s a reason why the adage brewers make wort; yeast makes beer has endured. Fermentation is everything! Ironically, the smallest ingredient a single-celled fungus in a recipe can hold the biggest sway in determining a homebrew s success or failure. Success can be found by mastering some simple essentials. Let s go over these Fermentation Essentials Documentation and Tracking Yeast Selection Starters and Pitch Rates Oxygenation Temperature Control Understanding Fermentation Stages Documentation and Tracking The importance of good documentation cannot be over emphasized. Information can be kept in a logbook or on computer file, which tracks all information pertaining to the brew. The following are suggestions for documentation and tracking information. Yeast Information Strain ID, Lot# and MFG Date Package Size Beer style, volume, date Temperature at pitching Starter Information Pitching rate in cells/ ml Fermentation Information Wort cooling/ temp and time Wort aeration Fermenter volume Yeast pitching details Gravity and temperature daily Time to half gravity or set target (i.e. 5 P) Final gravity Cooling time and date Forced ferment sample Fermentation Essentials 1

2 Yeast Selection Dry Versus Liquid Dry Yeast today is just as good as liquid Yeast. It really comes down to what you prefer and the selection that is offered to you. Refer to Liquid Versus Dried Yeast: An Old Debate Revisited. Choosing a House Yeast The reason why many breweries rely on one workhorse yeast and a few specialty strains is more than sheer economics. Brew a batch, split it, and ferment under the same conditions with two similar yeasts. It s the only way to determine, for example, whether one prefers Wyeast 3068 or WLP300 for a hefeweizen. There are no wrong choices. Once a few strains are well understood, branch out and try something new, like the seasonal offerings from Wyeast s Private Collection or White Labs Platinum Series. Prepping Dry Yeast Regardless of the yeast type or choice, it must be properly prepared before pitching. Dry yeast can be sprinkled directly on the wort, but this isn t recommended. The cell walls of dehydrated yeast are fragile. During the first moments of hydration, the yeast are unable to regulate what passes through the cell walls. Thus, the shock of absorbing wort directly can cause a great deal of attrition perhaps as much as 50 percent. So not only would the wort be under-pitched, the dead yeast cells will begin to break down and affect the flavor. For these reasons, dry yeast must be hydrated first. To hydrate one pack, heat 100 ml of water to about 105 F (41 C). Sprinkle the yeast on the water, avoid clumping, cover with a paper towel, and allow to sit for 15 minutes. Gently stir until the mixture has a creamy consistency, and allow it to sit for a few more minutes. Let the covered mixture cool to within 10 to 15 F of the wort temperature and pitch. Another recommended aid for hydrating dry yeast is the addition of Go Ferm, a yeast hull-based nutrient that provides the building blocks for the cells to reconstitute themselves. Starters and Pitch Rates Making a starter is easy. Prepare a 10 percent solution by adding 150 grams of extra light DME into 1500 ml of water with ¼ teaspoon of a yeast nutrient blend. Boil the wort in a sauce pan for 10 minutes. Cover the pan, place into an ice bath until cool, and pour into a sanitized clear growler. Add the yeast. Aerate by shaking. The growler can be loosely covered with sanitized aluminum foil. If possible, give the growler a shake every few hours to introduce oxygen, which will increase the cell count. A better method is to use an Erlenmeyer flask and a stir plate. Boil the starter in the flask on the stove s lowest power burner, being careful to avoid a boil-over and subsequent mess. A few Fermentation Essentials 2

3 drops of Fermcap-S, an antifoam agent, will lessen the chances of a boil-over. When the boil is finished, add a sanitized stir bar, cover the flask with sanitized foil, immerse in an ice bath until room temperature, and add the yeast. The vortex from the stir bar will introduce oxygen continuously, resulting in a much higher cell count than could be achieved by a starter in a growler. For high-gravity worts, the starter must be stepped up to increase the cell count even further. Once starter activity slows, cool the growler or flask to crash the yeast, rewarm to room temperature, pour off spent wort, replace with fresh, cooled wort, and repeat the process. At pitching time, sanitize the mouth of the flask or growler with rubbing alcohol. Pour off the spent wort, re-suspend the yeast, and add to the beer. If using a flask with a stir bar, be careful not to pitch the stir bar with the yeast. Standard Pitching Rates From Wyeast: STYLE GRAVITY PITCHING ( F) FERMENTATION ( F) PITCH RATE (MillCells/ml.) Ale <1.060 >65 > Ale >65 > Ale >1.076 >65 >65 >18.00 Lager* <1.060 >65 < Lager* >65 < Lager* >1.076 >65 <60 >18.00 Lager <1.060 <60 < Lager <60 < Lager >1.076 <60 <60 >24.00 * Technique of pitching a lager warm, allowing fermentation to begin, and cooling to the desired fermentation temperature. How Does Pitch Rate Affect My Beer? Pitch rates make a dramatic difference in the final flavor and aroma profile of any beer. Ester production is directly related to yeast growth as are most other flavor and aroma compounds. A low pitch rate can lead to: Excess levels of diacetyl Increase in higher/fusel alcohol formation Increase in ester formation Increase in volatile sulfur compounds High terminal gravities Stuck fermentations Increased risk of infection High pitch rates can lead to: Very low ester production Very fast fermentations Fermentation Essentials 3

4 Thin or lacking body/mouthfeel Autolysis (When a yeast cell dies, it ruptures - releasing several off-flavors into the beer.) Oxygenation Providing adequate oxygen is critical for yeast. Under normal circumstances, yeast metabolize sugars under anaerobic (oxygen-free) conditions to produce alcohol and carbon dioxide. However, during the yeast s initial growth phase, oxygen is needed for the yeast to produce the sterols to synthesize their cell walls. Strong cell walls are needed for reproduction and for yeast health. The production of alcohol is toxic for yeast. Strong cell walls will provide protection. Boiling of the wort drives the oxygen from the wort. Pouring the wort back and forth from one bucket to another Shaking or rocking the carboy back and forth Aquarium pump with in-line sanitary filter and sanitized air stone Pure oxygen with sanitized air stone Method DO ppm Time Siphon Spray 4 ppm 0 sec. Splashing & Shaking 8 ppm 40 sec. Aquarium Pump w/ stone 8 ppm 5 min Oxygen with an Oxygen Stone Using a.5-micron stone and a flow rate of 1 L O2 / min, you need around 60 seconds to get 9 ppm, as shown: 30 seconds pure O ppm 60 seconds pure O ppm 120 seconds pure O ppm When oxygenating a higher-gravity wort, you need higher oxygen levels - roughly proportionate to the amount of yeast. However, it's usually recommended to reoxygenate after the yeast have time for a cell division, This will result in a cleaner-flavored beer. Obviously, if you want your beer to have more off-flavors (specifically acetaldehyde and diacetyl), then a second dose of oxygen is counter productive. Keep in mind these values are also temperature dependent. The cooler the wort is, the better your ppm aeration will be in the end. Temperature Control The first step is to determine the proper fermentation temperature for the yeast strain. Guidelines are available on the manufacturers websites. However, personal preference through experimentation also comes into play. Fermentation Essentials 4

5 Regarding Belgian brews, don t fall into the trap of fermenting too warm. Many of the fermenters in Belgian breweries are shallow and engineered to work at warmer temperatures. Taller, five-gallon carboys present a different set of thermodynamics. As a rule, ferment Belgian beers in the upper 60s in degrees Fahrenheit and then slowly raise the temperature to the lower 70s toward the end of fermentation. This will avoid excessive phenolic and solventy flavors. First thing is to find a climate controlled room. Heating Brew belts, Heating pads and wraps are available to keep fermentations warm during colder months. An aquarium heater in conjunction with a water bath in a storage tub. Cooling Fermentation creates it s own heat. More often than not, the carboy will have to be chilled, especially during the summer and in warmer climates. Place the carboy in a pan filled with water. Wrap a towel around the carboy and let the towel wick up the water. The heat loss from evaporation will cool the vessel. This process can be accelerated with a fan. Place the carboy in a water bath inside an Igloo cooler and cycle 24-ounce soda bottles filled with frozen water as needed. Heating and Cooling Refrigerator and small space heater connected to a Ranco two-stage controller to regulate my fermentation temperatures. A plastic cap with a built-in thermowell and blowoff attachment is placed on the carboy. The Ranco probe is inserted into the thermowell, which extends into the wort. This way I can get an exact temperature reading and stay within a degree of the desired target. Once the temperature has stabilized and fermentation has started, let the yeast do its job. Understanding Fermentation Stages Fermentation is usually divided into three stages: primary, secondary, and conditioning (or lagering). Fermentation is when yeast produce all of the alcohol and aroma and flavor compounds found in beer. Manipulation of temperature, oxygen levels, and pitch rate as well as yeast strain selection will all dramatically affect the production of aroma and flavor compounds produced during fermentation. Primary Fermentation The primary stage of fermentation begins when the yeast is introduced into cooled, aerated wort. The yeast quickly utilize the available oxygen to produce sterols, a vital compound for culture expansion. When the oxygen is gone, the yeast switch to the anaerobic phase where the majority of wort sugars are reduced to ethanol and CO2. Yeast growth occurs during primary fermentation. The extent and rate of yeast growth is directly related to the production of aroma and flavor Fermentation Essentials 5

6 compounds. The temperature of the primary fermentation should be regulated according to the desired flavor and aroma profile. The following is a guideline: Primary Fermentation Temperatures: Ales: 62 F 75 F (17 C 24 C) Lagers: 46 F 58 F (8 C 14 C) *Note: Lager fermentations can be started warmer (~60 F, 15.5 C) until signs of fermentation (gravity drop, CO2 production, head formation) are evident. Cool to desired fermentation temperature once signs of fermentation are observed. Wheat and Belgian styles: 62 F 85 F (17 C 29 C) Secondary Fermentation The secondary stage of fermentation refers to the stage of fermentation after the majority of the wort sugars have been consumed and there is a sharp decrease in the rate of fermentation. During this period, most of the final sugars are depleted and some secondary metabolites are converted by the yeast. Yeast flocculation and settling begins to occur due to the increase in alcohol content and the depletion of sugar and nutrients. Diacetyl reduction takes place during secondary fermentation and during the diacetyl rest that some brewers incorporate into the secondary stage of fermentation. Secondary Fermentation Temperatures: Ales: Same as primary fermentation (higher temperatures will increase diacetyl reduction rates) Lagers: 40 F - 60 F (4 C - 15 C). Some brewers allow the beer to increase in temperature to speed the diacetyl reduction. This increased temperature is usually only sustained for 24 to 48 hours. Wheat and Belgian Beers: Same as primary fermentation (higher temperatures will increase diacetyl reduction rates). Conditioning The conditioning stage takes place when the terminal gravity has been reached and the tank is cooled to refrigeration temperatures (31 F - 38 F, 0 C - 3 C). During this time the yeast continues to flocculate and settle. The yeast also conditions the beer by reducing various undesirable flavor compounds. Ales do not benefit from long conditioning times like lagers do. The desirable flavors in ales will decrease with age and therefore it is recommended that conditioning be as short as possible before packaging. Exposure to oxygen at this stage is extremely detrimental to beer quality. Conditioning Summary: Most of the yeast is removed from beer Formation and precipitation of haze forming proteins Reduction and mellowing of harsh flavors Reduction of sulfur compounds, diacetyl, and acetaldehyde Flavor stabilization Fermentation Essentials 6