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Boiling the wort, with the addition of hops, extracts the hop alpha acids and isomers and dissolves them, stops enzyme action, kills bacteria, fungi us, and wild yeast, precipitates and coagulates undesired proteins, stabilizes salts in solution, and boils off undesired harsh hop oils, malt oils, sulfur compounds, ketones, and esters. A full, rolling boil for at least one hour is necessary to make quality beer.

PROBLEMS ENCOUNTERED WITH THE BOIL are many if the wort is not boiled, not boiled for one hour, or not boiled vigorously. Not boiling risks contamination from fusarium mold (on the barley), bacteria, wild yeast, and further Saccharification (undesired) by enzyme action. This may produce diacetyl, DMS, sulfury notes, cooked vegetable, sourness, acidness, garbage-like taste and smells, and moldy notes. The wort must be sanitized.

Not boiling for one hour risks under utilization of hop acids, and the bittering level may be off. Additionally, the head may not be as well formed due to improper extraction of isohumulones from the hops. A good rolling boil for one hour is necessary to bind the hop oils to the albumin’s, forming colloids that remain in the beer and help form a good stable head.

A rolling boil aides in the removal of undesired volatile compounds, such as some bitter hop compounds, esters, and sulfur compounds. Beer made without a rolling boil may be more astringent and be more prone to DMS formation

Clarity will be also be affected by not using a full hour rolling boil, as there will not be a good hot break to take out the undesired proteins. This will also affect shelf life of the bottled beer, as the proteins will promote bacterial growth even in properly sanitized beer bottles over time.

The preservative qualities of hops will also suffer greatly if the wort is not boiled for one hour, as the extraction of the needed compounds will be impaired.



Boiled wort must be cooled as quickly as possible. This is done to prevent infection, prevent DMS formation chemically in the wort, and provide a good cold break to precipitate out proteins and trub.

The best way of cooling is with a wort chiller. Two varieties are commonly available to homebrewers: counter-flow (used by breweries), and full-immersion. Either variety will cool 5 gallons in about 10-15 minutes to yeast pitching temperature. Using cooled, sanitized (boiled and chilled) add water with the small batch method is also acceptable, if the carboy is at yeast pitching temperature (90 degrees or less) after everything is mixed.


stem from slow cooling and improper handling of cooled wort.

Infection from bacteria and wild yeast will occur when the temperature drops below 150 degrees. They will multiply with astonishing speed at these higher temperatures. Diacetyl and DMS-producing wort bacteria will definitely taint slow-cooled beer, giving DMS, butterscotch, cooked vegetable and sulfury tastes and aromas to the final beer.

Additionally, slow cooling will cause certain chemical reactions to occur in the wort that will cause DMS to form. This DMS is not due to contamination or wort bacteria, but tastes/smells the same and will be impossible to remove.

Unsatisfactory cold break will occur if the wort is cooled too slowly. Poor cold break will leave undesired hop components and proteins and gums in the beer. These become insoluble as the wort is suddenly chilled, and drop out to the bottom of the fermenter and will not be re dissolved. The same compounds have time to be re-absorbed when the wort is slow-cooled. These compounds will result in chill haze and encourage the development of certain bacteriological off-flavors.

Using tap water which has not been boiled and chilled for carboy cooling using the small-batch boil method runs the risk of adding any bacteria (such as coliform) that are often present in tap water.


Oxygen needs to be introduced into the wort to promote yeast development during the lag phase, when it is living and reproducing aerobically. This is done by aerating the wort.

Aeration of the wort is generally done by shaking the carboy vigorously. This is the only time that oxygen is to be introduced in the beermaking process

Aeration should be done in a relatively clean (biologically speaking) environment. If the air smells bad aerate the beer somewhere else.

Aerating hot wort has the following advantages:

No risk of contamination from air; better cold break by oxidizing some protein fractions.

Aerating hot wort has the following disadvantages: Polyphenols turned to tannins; oxidation of hop resins; darker color.

Aerating hot wort should not be done for very pale, very dark, or very full-bodied worts, or for delicate styles such as Viennas.


include under aeration and overaeration.

Under aeration will cause the yeast to prematurely stop fermentation, resulting in stuck fermentation, excessively sweet wort, diacetyl and acetaldehyde remaining and not re absorbed, and sulfur from yeast autolysis.

Overaeration may result in excessive formation of ethyl acetate, giving solventlike acrid aroma and taste, and banana aroma.


Fermentation is generally divided into two stages: Primary fermentation and Secondary fermentation.

Primary fermentation refers to the initial, active phase when the yeast is forming the kraeusen head. During this stage the yeast is actively fermenting the malt sugars to alcohol and carbon dioxide.

Primary fermentation is generally over when the kraeusen head disappears. At this time about one -half to two-thirds of the fermentables have been converted. Primary fermentation will generally take anywhere from three to ten days, depending on the yeast strain, the fermentation temperature, and the dextrin content of the wort.

Secondary fermentation allows the slow reduction of the remaining fermentable sugars. This may take from seven to twenty-one days, depending on the yeast strain and the amount of fermentable sugars in the wort. Generally, ales will require a shorter period of secondary fermentation than lagers. During this period the yeast will begin to flocculate as the last of the sugar are used up. It is important that no oxygen be allowed into the beer at this time. Most brewers recommend racking the beer to a secondary fermentation vessel at the end of the primary fermentation.

Fermentation should proceed at the proper temperture for the yeast strain and style of beer being brewed. Sudden variations in temperature in excess of 6 degrees F. per day must be avoided during fermentation. Strong light should also be excluded from fermenting vessels (especially glass carboys)

Gas locks should be of the type that will not permit lock water to be sucked down into the carboy. Locks should not permit a great pressure to build up in the carboy.

If using a blowout technique (recommended), make sure that the blowout hose is sanitized before installing it on the carboy. Suspend it above the catch bucket, so that there is no possibility of blowout being sucked back into the carboy should the carboy be cooled. The hose should also be big enough that pelletized hops will not cause it to foul, resulting in a blown cork and kraeusen foam on the floor. Never fasten or seal the cork to the carboy!


include the following: underpitching; overpitching; improper temperature; rapid temperature variations; light-struck; excessive fermentation time, stuck fermentation

Pitching is the act of adding the active yeast starter to the chilled and aerated beer wort.

Underpitching will result in excessive contamination. The wort is in its most vulnerable state after cooling and prior to high-kraeusen blowout. Sufficient yeast must be pitched to bring about high-kraeusen blowout within 24 hours, and ideally less than 12 hours after cooling. This time between pitching and high-kraeusen is called "lag time", and the smaller the lag time the better. Underpitching will give any contamination a chance to establish itself in the beer, resulting in DMS, diacetyl, cooked vegetable, and similar off-flavors. Another result may be a delayed reaction in the bottled beer, resulting in overcarbonation from a seemingly normally-carbonated beer left for two or three months.

Overpitching will generally result in "yeast bite", a noticeable yeasty taste in the beer. Re-using all of the slurry from the bottom of a primary fermenter in a new batch will usually overpitch the batch. Overpitching results in rapid consumption of the limited amounts of dissolved oxygen, simple sugars, and yeast nutrients. This will result in yeast autolysis, or self-digestion, and will result in yeasty, sulfur-like flavors.

The optimal amount of yeast is about 0.4-0.6 ounce of pasty, thick yeast sediment per gallon of wort, or about 2.0 to 3.0 ounces per gallon. For dry yeasts this translates to no less than 12 grams of yeast, activated before pitching by dissolving in 90 degree F sanitized water (not wort or sugar water) for about 20 minutes. For cultures, a starter of at least 16 oz of wort (for five gallons) should be prepared and allowed to go into high kraeusen before pitching into the wort. Using less than this amount (such as directly from a bagged culture package) will underpitch the batch and result in an excessively long lag time.

Improper temperature will result in a totally different beer from what is intended. Too high a fermentation temperature for lager yeasts will, in most cases, result in fruity-estery tastes that are uncharacteristic of lagers(unless you are making a steam beer with a heat-tolerant lager yeast). Tocold a temperature with an ale yeast can cause it to stop working and flocculate out prematurely, resulting in a stuck fermentation, with accompanying diacetyl, acetaldehyde, and excessively sweet tastes.

Rapid temperature fluctuations will often result in production of DMS and other sulfur-like compounds, particularly with certain lager strains. It can also disrupt the yeast life cycle, resulting in premature flocculation and mutant yeast growth. Temperature changes should be limited to no more than six degrees (Fahrenheit) per 24 hour period once the yeast has established itself in the wort.

Light can destroy a fermenting beer in the same manner as it can destroy bottled beer, by causing a breakdown of hop oils to undesirable sulfur compounds. This will result in a skunky taste and aroma. Keep glass carboys away from strong sources of light at all times.

Leaving the beer in contact with the yeast sediment and trub for any extended length of time is undesirable. Such trub can contribute many off flavors such as medicinal, sulfury, diacetyl, and astringency. Yeast autolysis (decay) can also provide food for any stray bacteria present in the beer and permit it to grow. While racking to a secondary is generally not necessary for most ales due to the short fermentation time, it is a good idea to carefully rack to a clean secondary any beers destined to be secondary-fermented or cold-lagered.

Stuck fermentations are generally a result of either premature flocculation of the yeast before it has a chance to properly attenuate the wort, or, in the case of high-gravity beers, a lack of alcohol tolerance in the yeast strain which causes it to die out and stop working before the fermentables in the wort have been consumed. "Rousing" the yeast, which can be done by gently shaking the sealed carboy, may sometimes result in the fermentation resuming sufficiently to complete the attenuation. Rousing must not result in additional oxygen being dissolved in the beer at this stage. Another method is to add more fresh yeast, in the form of a starter culture. This is the best method of completing the fermentation of a high-alcohol beer started with a normal yeast strain.

Often times a fermentation is considered "stuck" when, in reality, all the fermentables have been consumed. A beer made with a high dextrine content

may only attenuate to around 40% - 45% of the starting gravity, with the high end gravity a result of the unfermentable dextrine content of the beer. No amount of rousing or repitching will result in a lower final gravity of such a beer.


Racking is the process of transferring the beer from one container to another, generally to leave behind unwanted trub. It is of utmost importance that racking be done without "splashing" the beer, or permitting oxygen to dissolve in it. Racking is usually done by means of a siphon. It is important when starting a siphon that the lips never come into contact with any part of the hoses that will contact the beer.


include splashing or aeration of the beer, poor sanitation, and contamination when starting the siphon.

Splashing and aerating the wort while racking can result in oxidization of the beer, which will give a sherrylike, cardboardy taste. It can also permit the formation of undesirable esters and sulfur compounds.

Microbiological contamination can also be introduced by splashing the beer at this stage. Poor sanitization, especially hoses or racking tubes that are dirty and therefore impossible to sanitize properly, will also introduce microbiological contamination. Starting the siphon by sucking on it will contaminate and usually ruin the beer.


The word "lager" in German means "to store". Lagering is the process of cold-aging beers made with lager yeasts. Lagering is done at colder temperatures than those used for primary or secondary fermentation. Temperatures between 32 and 35 degrees are generally used. Time for lagering ranges from a few days to a few months, depending on the starting gravity and dextrin content of the beer.

Cold lagering is generally done only for beers made with slow-fermenting lager yeasts (S. uvarum), although short to medium periods of cold-aging will help almost any beer with active yeast.

Lagering will act to improve the beer by smoothing out the harsh flavors present. During lagering many of the tannins present in the beer combine with the haze-forming proteins and settle out. The yeast slows down but still continues to work, converting slow-fermenting sugars such as maltotriose and the higher dextrins. As these sugars are consumed the yeast will then act to consume some of the undesired esters and sulfur compounds that may have been formed by inadvertent oxygenation, light-striking, or yeast autolysis. The yeast then will go dormant and flocculate out, clarifying the beer


include oxygenation and rapid temperature fluctuations. Oxygenation will result in the formation of diacetyl and oxidized fusel oils, especially with darker beers. Higher temperatures and rapidly fluctuating temperatures encourage the formation of aldehydes (which give beers stale, cardboardy-like flavors) and yeast cell decomposition, which results in sulfury, stale and solventlike flavors, and can contribute to later instabilities in the bottled beer.

Beer should always be racked off the trub in the primary fermenter to a secondary before lagering.


Priming is the term for adding extra fermentables to a beer just prior to bottling, to permit the yeast to carbonate the beer. The renewed yeast activity should be just sufficient to force the CO2 produced into the beer at the correct gas volume level. Note that most commercial breweries force-carbonate their beers by pumping CO2 gas into them through a carbonation stone(a porous stone that disperses the CO2 into very small, fine bubbles).


are usually due to using to much priming sugar, too little, storing newly bottled beer in a too-cold location, not dissolving sugar in water and boiling, weak yeast, or using wort or malt extract (instead of corn sugar) when priming a lager beer.

Corn sugar is generally used by homebrewers for priming as it is easy to use and, in small amounts, does not impart any flavors to the beer. The amount of corn sugar used for priming is critical to the proper carbonation of the beer. Generally, 1/2 to 3/4 cup of corn sugar per 5 gallon batch of beer will give a proper carbonation level. Excessive amounts of sugar will cause overcarbonated beer, "crawlers", "gushers", or exploding bottles ("bombs").

Dry powder malt extract or wort saved from the boil ("gyle") can also be used instead of corn sugar. However, there are risks with priming with malt or gyle. For example, lager made from yeast strains that give fruity flavors at higher temperatures must not be allowed to carbonate at temperatures above those used for primary fermentation, when primed with malt or gyle, or fruity flavors will develop. Generally it is better to prime lagers with corn sugar.

Corn sugar should be added to water and boiled for at least five minutes before being added to the racked beer. This sanitizes everything and also pre-dissolves the sugar for easier use by the yeast.

Primed beers should be stored for at least two weeks at temperatures between 60-70 degrees to permit the yeast to work. Beers made with lager yeast and primed with malt or gyle should be stored at 50-55 degrees for about a month to prime. Lager beers that have been lagered for long periods (4-6 months) may require a longer period to prime, or, in some cases, a fresh repitching of yeast.


Bottling (or kegging) is the process of transferring the primed, finished beer into the pressure vessel (bottle or keg) so it can prime to the proper carbonation level.

Bottling is similar to racking and many of the same problems can develop, particularly if oxygen is introduced during the bottling process. Avoid using auto-shut-off bottle fill tubes if they splash excessively.


can occur if the beer is splashed or oxidized, if the bottles are over or underfilled, or if the bottle caps are not properly sanitized.

The optimal fill level in a beer bottle has the liquid level about one inch below the lip of the bottle. Insufficient head space will interfere with the natural carbonation process and result in undercarbonated beer. Too much head space will permit excessive oxygen to dissolve in the beer, resulting in off flavors.

Caps should be boiled in water at least two minutes before use. This sanitizes them and softens the plastic sealing material, insuring a better closure.

Flushing bottles with CO2 gas both before filling and before capping is a technique used by some brewers, especially those with kegging systems. Flushing greatly reduces the chances of oxidation damage in bottled beer.


Beer should be stored in a dark, constant temperature environment. After the beer has primed, the colder the storage the better. Cold storage greatly increases the life of fresh beer. Beer should not be subjected to rapid or large temperature variations, heat above 70 degrees, or strong light.


generally result from high temperatures or rapid temperature fluctuations. High temperature (>70 degrees) storage will result in premature "staling", with sherrylike and oxidized tastes appearing after only a few months. Autolysis of the sediment, especially combined with any starches or proteins in the beer, will be accelerated and may turn a beer that’s been perfect for months into a gusher or a bomb. Rapid temperature fluctuations accelerate the effects of high-temperature staling. Intense light (sunlight) will result in skunky flavors.

The ideal storage location for beer is a constant-temperature cellar or a refrigerator (if you cellar goes above 70 degrees in the summer).