Brew for Africa - 011-949-1009 / 076-173-9196

The Home Brewing Blog

Brewing problems and how to resolve them

Home brewing is both simple and complex at the same time. The process itself is fairly straightforward, but at the same time there are a gazillion factors involved, each of which can affect the eventual result. In this chapter we will take a look at the most common brewing hiccups that may occur during various stages of brewing.

Mashing and Sparging

The number of problems that can occur during mashing and sparging is limited, but there are a few factors that may lead to the following, most common, issues.

Low mash efficiency.
This is characterized by a light, watery, thin wort that is too light both in colour and in gravity. The cause of low mash efficiency is almost always insufficiently crushed grains. The solution is to adjust the grain mill to create a proper grist.

Low extraction efficiency.
Another possible cause of too light and thin a wort occurs during sparging, due to an incorrect distribution and flow of the sparging water. The water should be sprinkled evenly across the top of the grain bed, and seep through it in an even fashion. Simply running water (e.g. from a kettle or tap) into the grain bed will create channels through which the water flows down immediately without actually running through most of the grain bed.

It is also important not to sparge too quickly. The sugar should have enough time to dissolve in the sparging water. Depending on the amount of grain and the brewing set-up used, proper sparging should take anything from 30 minutes (for most home brewing buckets, pots and/or urns) to 2 hours or more for larger volumes.

Lumpy mash.
Sometimes a mash contains lumps or "dough balls". This happens when the grain is not properly mixed in with the strike water. This most often  occurs if the grains are added to the mash tun before the strike water, followed by insufficiently stirring of the mash. The way to prevent this is to add the water to the mash tun, then gradually add the grains while stirring properly to prevent any dry pockets from forming.

Stuck sparge.
A "gummy" mash or a grain bed that is too compact can prevent the sparging water from flowing through the grain bed. Instead the water will simply sit on top of the grains and not go anywhere. The best way to prevent a gummy mash is to incorporate rests at the proper temperatures into the mashing process to break down the gluey starches or proteins that cause a stuck sparge.

The exit tube from the mash tun may also be blocked. If this happens frequently, the design of the mash tun and its manifold (if the mash tun contains one) might be the problem. Redesign the manifold and/or wort outlet if necessary.

A quick solution to get a stuck sparge going again is to force some air or water back into the mash tun's exit tube. This tends to dislodge some of the grains and can lift the grain bed slightly, which loosens it. Adding boiling water to get some heat into the grain bed, especially when 'gummy' ingredients play a role, may also help to thin the mash. Add hot water, stir, perform another wort recirculation step as outlined in previous chapters, and sparging should then work as usual.

Cloudy wort.
After a proper recirculation of the wort through the grain bed prior to sparging, the green wort coming from the mash tun should be reasonably clear. If it is opaque and recirculation does not clarify it, this might indicate too many unconverted starches still present in the wort. In this case the saccharification was incomplete at the time of sparging. The grain bill may have had insufficient diastatic power (especially if large amounts of non-diastatic adjuncts are involved). The temperature may have been too low or too high, or the duration of the mash may have been too short. These factors will all have to be investigated and adjusted where necessary. Use an iodine test to ensure no residual starches are left in the mash before lautering.

The problem may also originate in the crush of the grains. If the grain is too finely crushed and contains too much powder, some of this will end up in the wort. Adjust your malt mill accordingly if this is the case. Note that proper wort recirculation prior to sparging will minimize the effects of a powdery crush to some extent.

Harsh bitterness or phenolic flavours in the beer.
If the finished beer has an unpleasant bitterness that can't be traced to excessive use of harsh bittering hops, or if it has a flavour reminiscent of insufficiently pickled olives, tannins may have been extracted from the grain husks. This is most often caused by a mash pH that is too high. This can happen when light coloured beers are being brewed with very hard, alkaline water, or when a small amount of grains is steeped or mashed in a large volume of water. Lower the pH of the strike water and/or the mash, and use no more than 3.5 to 4 litres of water per kilogram of grain for steeping or mashing.


Apart from the sudden boil-overs that most home brewers know all too well, there is not too much that can go wrong during the boil. If the volume and gravity of the wort extracted from the grains is within acceptable limits, then the beer's hop bitterness and other flavours should end up within the expected ranges as well. If they don't, the boil gravity of the wort is the most likely culprit. Take a pre-boil sample of the wort, cool it down to room temperature and do a gravity reading to ensure that you have not overshot or undershot your pre-boil gravity target range.

Other than that, the most common problems are wort colour and scorching.

If the wort ends up too dark and the beer ends up being too strong, the wort has been over-concentrated due to too much water boiling off. If this happens, some water should be added during the boil to make up for the loss. Note that the use of water with a high alkalinity also promotes wort darkening, and h gravity worts tend to darken more during the boil than light gravity worts.

The wort may also scorch if too much heat is applied during the boil, either from over-powered electric heating elements or a gas flame that is turned up too high. This tends to happen with malt extract more often than with a full grain wort, since malt extract may not have been stirred in properly and can sit in higher concentrations at the bottom of the brew pot or wort kettle. However, all wort can be scorched if heated excessively, which darkens it and creates more dark, complex sugars that result in a beer that is darker, has a higher finishing gravity and has a different flavour than intended.


The fermentation may look like a step in the process that is simpler than mashing, but what happens during this stage is actually far more complex. A variety of things can go wrong in the fermenter. We can't discuss all of them here, but the most common ones are outlined below.

Long lag time or no start of fermentation at all.
While it always takes some time for the yeast to wake up and get on the job (the "fermentation lag" or "lag time"), an excessively long lag time is an indication that the yeast is not having a great day and, consequently, is likely to do a sub-standard job. There is a number of factors that may cause a long fermentation lag. The main ones are insufficient wort aeration, an insufficient quantity of yeast, insufficient yeast health and viability (the yeast may be too old or may have been stored under the wrong conditions), too high a wort temperature (leaving the yeast stunned or dead) or too low a wort temperature (causing the yeast to go dormant). Ensure healthy yeast, sufficient wort aeration and the right wort temperature, and fermentation should start within 6-12 hours after pitching. A proper wort should contain all the nutrients to support the yeast's growth phase, but adding some yeast nutrient is never a bad idea when it comes to ensuring a good fermentation.

No visible fermentation or fermentation completes very quickly.
Many home brewers tend to judge the progress of the fermentation by the amount of carbon dioxide gas bubbling out of the airlock. However, this is not always a good indication. The fermenter may have a leak, through which the slight overpressure escapes without creating bubbles in the airlock. The fermentation may also complete quickly (but properly) depending on starting gravity, yeast type and wort temperature. The key to verifying that fermentation proceeds along normal lines is to take gravity readings, and to observe the Krausen that floats on top of the beer. If Krausen forms, fermentation takes place. If the wort gravity drops, fermentation takes place. If the gravity is low and stable, the primary fermentation is complete. These observations are all far more important (and accurate) than the amount of bubbles coming out of the airlock.

Stuck fermentation.
Sometimes a fermentation stops long before the expected finishing gravity of the beer has been reached. There are several common causes that may lead to a stuck fermentation.

The wort temperature may have been too low, causing the yeast drop out of suspension. The yeast then sits on the bottom of the fermenter and no longer comes into contact with unfermented sugars. Bring the temperature of the wort back up to the proper level, then rouse the yeast by gently stirring it to bring it back into suspension and into contact with unfermented sugars. Use a sterilized spoon or paddle to stir the yeast back into suspension and avoid splashing, because you don't want to aerate the beer after yeast has been pitched. Don't try to stir the entire sediment back in suspension, as this sediment "cake" can also other substances which should not all end up in the beer.

Another problem may be that the yeast is insufficiently healthy, or is faced with adverse conditions such as limited oxygen and yeast nutrient availability, either of which inhibit yeast growth. This causes the yeast to eventually die from old age without producing any new cells to take over when previous generations die out. The solution in this case is to pitch more, fresh yeast.

The composition of the wort may also be a problem. Yeast adapts itself to the types of sugars that it encounters. When the wort contains a high percentage of refined sugars such as dextrose or sucrose, the yeast will adapt and begin to produce the enzymes that process these sugars. But in doing so, it may lose the ability to produce the enzyme needed to process maltose, which is the main fermentable sugar in wort. Therefore a high refined sugar content may lead to unfermented maltose being left behind in the wort once the yeast is done fermenting the refined sugars. The solution in this case is also to pitch more, fresh yeast once the fermentation stops.

Prolonged and continued bubbling.
This does not always indicate a problem. It may just be that the fermentation proceeds slowly due to low temperatures. There may also be a lot of sugars in the wort that ferment slowly (especially in dark worts) or the starting gravity of the beer was very high and the yeast simply needs more time to deal with all the fermentable sugars. There is, however, another possibility: an infection with bacteria or wild yeasts. These can sometimes ferment sugars that would otherwise be unfermentable, such as dextrins and lactose. These yeasts and bacteria are known as "gusher bugs", because they also cause the beer in the bottle to be over-carbonated. Beers infected with gusher bugs have very little taste and almost no body, in fact they are are much like alcoholic, sparkling dish water.

High finishing gravity.
This is not necessarily a problem. Sometimes a fermentation is considered to be stuck, but is in fact complete. The finishing gravity of a beer may simply be high if the wort contains a lot of unfermentable sugars. This is especially the case with beers brewed with significant percentages of malt extracts, with beers that have been mashed at the high end of the temperature range, or when the grain bill contains a large amount of dextrin malt. Beers that have a high starting gravity (such as full-bodied strong ales and barley wines) also tend to have a higher finishing gravity. The properties of the yeast also play a role: a high attenuation yeast will ferment the beer out much further than a low attenuation yeast will.


The development of carbon dioxide in the bottle is the product of fermentation under pressure. Typical problems at this stage are overcarbonation or undercarbonation.

If the beer is overly fizzy or foamy when the bottle is opened and the beer is poured, this is most often the result of bottling too early. If
the beer hasn't fully fermented out before bottling, then the remaining fermentation will take place in the bottle, adding more carbonation to what is already being provided by the priming sugar. Note that some dark beers can take several weeks to ferment out completely, because they contain sugars that ferment very slowly. If a properly carbonated beer is overly fizzy when poured, that usually means that the beer isn't cold enough.

If the beer does not carbonate, and the beer is still flat after spending several weeks in the bottle, there are only a few possible causes.


  • No viable yeast. Either all yeast was flocculated out of suspension (some beer finings such as Isinglass can remove more yeast than is desirable) or the beer has spent too much time in the fermenter so that the yeast has died of old age. (This is also likely to cause autolysis flavours, as discussed below.) If this is the case, the beer will not only be flat but also taste sweet due to the presence of unfermented priming sugar. Opening the bottle, adding a knife tip of dry yeast and recapping the bottle may save your batch of beer. Do not add more priming sugar, because this will cause the bottle to overpressurize and potentially explode.
  • Not enough priming sugar, or no priming sugar at all. Opening the bottle, adding priming sugar and recapping the bottle may remedy the problem, but also introduces the risk of over-priming, which may lead to dangerously pressurized bottles that may explode.
  • Low temperature. The yeast needs to be within a temperature range at which it is active (which generally means room temperature) in order to carbonate the beer. If the beer is too cold, the yeast will be insufficiently active and little or no carbon dioxide gas will be produced. This can easily happen when bottles of beer are stored in unheated rooms, garages or sheds during winter. Bringing the bottles back up to room temperature and turning them upside-down once in order to bring the yeast back into suspension is enough to fix this problem.
  • Leaking crown seals. If the bottles are improperly capped (wrong type/size of crown seal, wrong type/size of capper tool) the cap may not provide an airtight seal in spite of the fact that it looks fine. In that case the carbon dioxide gas slowly escapes, leaving the beer mostly uncarbonated. Use the proper bottles, caps and capper tool for your next brew.

Funny smells and flavours

There are quite a few possible problems that manifest themselves in the form of flavours or smells when the finished beer is being poured poured into the glass. Unfortunately, at this point in time it is usually far too late to do anything about it. The best the brewer can do is to analyse the problem and its causes, and prevent it from occurring again in the future.

This substance is characterized by a cidery aroma, a flavour of green apple, and/or a smell of green apple or freshly stripped tree bark. Acetaldehyde is an intermediate compound in the production of alcohol by the yeast. If the yeast is stressed, too much acetaldehyde may be left in the beer. Causes of acetaldehyde include overpitching, unhealthy or stressed yeast, as well as the presence of too many sugars that the yeast struggles to digest. This can happen when too much sucrose (a.k.a. table sugar) is added to the wort or when food grade (not brewing grade) malt extracts are used. Some, most or all of the acetaldehyde may disappear over time during lengthy bottle conditioning and maturation, but its breakdown can cause the production of other flavours which may or may not improve the overall flavour of the beer.

Astringent / tannin / grainy flavours.
Astringency differs from bitterness by having a puckering quality, like sucking on a tea bag. It is a dry, powdery flavour and is often the result of tannin extraction from the grain. Speciality grains may have been steeped for too long, too hot, or in too much water. The pH of the mash might have been too high, the mash may have been oversparged, or the sparging with water may have been too hot. These flavours may also be produced when the remaining Krausen, which floats on top of the beer and clings to the sides of the fermenter during and after fermentation, is stirred back into the beer. Overly grainy or husky flavoured beers may also result when the husks of the malt have been shredded too finely or ground into a powder during milling.

Characterized by a buttery or butterscotch flavour, diacetyl is essential in some beer styles (especially smooth, sweet ales such as Belgian and English ales). However, it is considered an off-flavour in other styles, most notably in lagers. Diacetyl production is mostly a factor of the yeast type and the fermentation temperature and, to a lesser degree, wort composition. It is usually formed early in the fermentation and re-absorbed during the later stages. Having a fermentation that starts hot (and therefore promotes the formation of diacetyl) but ends at a lower temperature (thereby inhibiting the re-uptake of diacetyl) can leave too much of this compound in the beer. Maturation and lagering at the right temperatures are the best way to promote the re-uptake of excessive diacetyl. However, sometimes other unwanted compounds are oxidized into diacetyl over time during lengthy maturations, which may either save or ruin a beer depending on its initial problems and its desired final style. For example, oxidation reactions may cause the formation of diactyl from the aceto-lactic acid that plays a role in yeast metabolism, especially during lengthy maturation periods. Beers with a long fermentation lag tend to be higher in diacetyl.

Dimethyl Sulphide (DMS).
This substance is most notable on the nose, making the beer smell like cooked vegetables (especially tinned sweet corn) or tomato sauce. Like diacetyl in ales, a moderate amount of DMS is not uncommon in many light lagers and is generally considered to be part of the style. In excessive amounts, however, it becomes a problem. DMS is formed constantly during the boil from compounds naturally present in the malt and, if the boil proceeds properly, is boiled off at more or less the same rate. Boiling the wort with a lid on the brew pot prevents the DMS from boiling off, and condensate that drops back into the wort during the boil reintroduces the boiled-off substances into the wort.

DMS is a common problem with food grade malt extracts, which have not been properly boiled during production. The DMS left in the malt extract can't be removed once the extract has been produced. Certain bacterial infections can also cause DMS to be formed, but then the flavour has a more rancid character (more reminiscent of cooked cabbage than of cooked sweet corn) and is usually accompanied by other off-flavours produced by the bacteria. A lengthy maturation may improve a beer with excessive DMS, but this also depends on the presence of other compounds. DMS is usually converted into acetaldehyde during lengthy maturations, which in turn may be converted into diacetyl. Sometimes this works, sometimes it doesn't.

Fruity esters.
Many ales rely on the presence of fruity esters which, as their names suggests, lend sweet, fruity and pleasant flavours to a beer. One ester in particular, isoamyl acetate, has a distinct banana flavour that is a signature flavour in certain Belgian ales and in German Weissbier. Other esters may cause aromas of candy, artificial fruit flavours and bubblegum which are acceptable in low levels in certain ales but not in higher levels, and in other styles they a always considered a defect. The most important factors in the formation of fruity esters are yeast genetics and fermentation temperature. Some yeasts produce lots of fruity esters, others only a low amount. They are formed at the higher end of the fermentation temperature range. If they are unwanted, then care must be taken to keep the fermentation temperature low, and to use a yeast with a low ester profile.

Grassy or metallic flavours.
Flavours and odours reminiscent of fresh cut grass are not common, but they do occur. They are linked to chlorophyll and are usually the result of improperly stored ingredients. Poorly stored malt can pick up moisture and develop musty smells, while aldehydes can form in old malt, producing more green grass flavours. Hops that are not properly stored or have not been properly dried prior to storage may also introduce chlorophyll and grassy aromas. Metallic flavours are usually caused by unprotected metals dissolving into the wort, but can also be caused by the hydrolysis of lipids in poorly stored malts.

Moldy aromas and flavour.
Molds are quickly recognized by their characteristic smell and taste. Black bread molds and mildew can grow in both wort and beer. Contamination is likely if the wort or beer is exposed to musty or damp areas during fermentation. Sometimes white or green mold colonies can form on top of the beer during fermentation. Strange green, white or light brown patches floating on top of the beer during or after fermentation are an indication of this particular form of infection.

Medicinal or leathery aromas and flavours.
These are the product of unwanted phenols. These can be caused by the presence of chlorine in the wort due to cleaning with chlorine-based products and not rinsing sufficiently. Chlorine compounds in the fermenter will create a substance known as trichlorophenol (TCP for short) which has a distinctive and unpleasant aroma and flavour. Wild yeasts that have infected the brew also may be the cause of these flavours.

Overly spicy, clove-like or astringent flavours.
These are the result of unwanted polyphenols. They can have several causes. A common one is the tannin that can be extracted from the grain husks due to steeping grains in too much water, as a result of oversparging the mash, or in response to a mash pH that is too high. Tannin is a polyphenol, and sometimes a hint of this particular flavour can be found in olives that have been under-pickled.

Another common cause of polyphenols is yeast, most often when the wrong yeast ends up in the beer. This can happen when the wort is contaminated with wild (airborne) yeasts, or when the beer is fermented with a yeast not suitable for the purpose. Underpitched, damaged or mutated yeast may also produce polyphenols.

Note that certain yeast strains (such as some Belgian ale yeasts and German wheat beer yeasts) produce certain amounts of phenols as part of their normal flavour profile. Some Belgian ales are fermented or bottle conditioned with local wild yeasts that can impart aromas on the beer reminiscent of horses (!) but in these beers this is considered appropriate and desirable.

Phenolic flavours may range from nasty (e.g. plasters and hospital gauze) to pleasant (e.g. spicy notes of pepper and cloves). The latter, in moderation, are desirable in some styles, most notably German Weissbier, but also in some Belgian ales. They are generally considered an off-flavour in most other styles, and are always a problem when present in excess.

Rough, sharp or "hot" alcohol or solvent-like notes.
This indicates the presence of fusel alcohols: high molecular weight alcohols such as amyl or butyl alcohols which are more suitable for cleaning purposes than for consumption. These alcohols can form if the fermentation temperature fluctuates or is too high, and sometimes if excessive amounts of yeast are pitched. Fusel alcohols are combined with organic acids to form the esters that are responsible for fruity flavours. Temperature fluctuations during the fermentation may cause these fusels (and other solvents such as acetone) to be formed during earlier stages of the fermentation but not be removed later.

Flavours of Marmite, stock cubes or barbecue sauce.
When yeast cells die from old age or other causes, they eventually fall apart and release the substances contained within the cell. This process is  known as autolysis. The released compounds steep meaty, Marmite-like flavours into the beer. Marmite is actually made from dead yeast, and this is also a main ingredient in stock cubes. In fact, dead yeast (which has been hydrolysed with salt, rather than autolysed from old age) is a frequently used ingredient in a variety of processed foods, because of the meaty flavour it can add to these products.

The most common sources of autolysis flavours are beer that is left in the fermenter (sitting on top of the yeast sediment) for too long, and the use of old yeast, which contains a large amount of dead cells.

Soapy flavours.
When fatty acids from the yeast cells break down in the trub, soapy flavours may result. Soap is in fact a salt of fatty acids. During a proper fermentation most fatty acids are combined with alcohols into fruity esters, but some will end up in the trub where they may eventually be saponified (i.e. turned into soap). The best way to prevent this is not leaving the beer on the trub for too long, and not to stir the trub back the beer. That is, of course, assuming that the soapy flavour is not simply the result of detergent residues left behind after cleaning the brewing equipment!

Smells of sour milk, rotten eggs or dirty diapers.
These delightful aromas are the result of bacterial infection, which in turn are caused by improper sanitation or lack of hygiene. Faecal and decomposition odours are usually the result of coliform or similar bacteria, while sour smells and flavours tend to result from lactic acid bacteria infections (most commonly Lactobacillus and/or Pediococcus strains). Note that lactic acid is considered appropriate in some sour beer styles, and that sulphur-like aromas in moderate quantities are normal for certain yeast strains.Lager yeasts especially can produce hydrogen sulphide during fermentation, which smells of rotten eggs but is not a result of beer spoilage. However, this odour should not be excessive. When in doubt regarding sulphur-like notes, allow the beer more time to ferment and condition to see if the problem sorts itself out.

Flavours and smells of vinegar.
Acetic acid (i.e. vinegar) may be produced if oxygen is introduced into the beer late in the fermentation when there are few sugars left for the yeast to digest. The yeast switches to an aerobic mode and begins to oxidize ethanol into acetic acid. Once formed, this acetic acid is impossible to remove. The way to prevent it is to avoid introducing oxygen into the wort after the fermentation has started.

Stale / oxidized flavours.
Oxidation is one of the most common problems with beer, including commercial beers. If the wort is exposed to oxygen at higher temperatures (typically over 30°C) the beer will sooner or later develop aromas of wet cardboard. Combined with fusel alcohols resulting from high fermentation temperatures, oxidation may also produce harsh, sharp and solvent-like hydrocarbons. Avoid aeration after the fermentation has begun; this is the only way to prevent the formation of these flavours.

Skunk / lightstruck aroma.
Skunky or cat musk notes in beer are the result of the harmful effects of daylight (especially sunlight) on the delicate molecules that are responsible for the hop flavours and aromas in beer. These are complex and fragile organic compounds, and the ultraviolet component in daylight breaks them down and converts them into chemicals known as thiols. Thiols are a group of malodorous compounds that naturally occur in faeces, the urine of cats and mice, skunk spray and other unpleasant substances. The chemical added to LP gas or natural gas to give it a detectable odour (methyl mercaptan) is also a member of the family of thiols.

Beer should always be kept out of direct sunlight in order to prevent the hop flavours from being converted into thiols, and should be packaged properly to minimize the amount of light entering the bottle. Brown glass protects beer much better from daylight than green glass does. Bottles made from clear glass offer no protection at all and are exclusively used for cheap industrial beers that have not been brewed with hops but instead contain chemically processed, pre-isomerized hop extracts that have a much better resistance to light.

Find us on Facebook ▲ Back to top