Beer Faults – A Guide to The Tastes and Smells of Bad Beer!

At some point in our brewing careers we are all going to make a bad batch. It’s a fact of life and is something we can’t change. For most of us this means committing the most cardinal of all sins….throwing your beer out.
But for some of us this just isn’t good enough. I for one like to know what went wrong and at what point and if I can save it, I want to know how. So here my friends is a guide to the disturbing world of the tastes & smells of bad beer.

Fruity or Vegetable Smells
This is caused by under aerating wort prior to pitching yeast. It can be caused by a long lag phase. In other words the yeast has taken too long to start fermenting. The cause could be not enough yeast pitched or the yeast is stale or infected. There is no cure for this.

Banana Odour
This is caused by the same things as above. That is the yeast is not aerated enough for good fermentation to start. Buy the time you get to taste it it’s to late, no cure.

Vinegar Taste & Smell
This is caused by acetic acid bacteria. Can be airborne by fruit fly or dust particles. If you the wort was aerated well, the yeast is off to a good start, the fermenter is well sealed and an airlock fitted, vinegar bacteria should be kept out. If infected, tip it out. No cure.

Lactic Acid Bite
Another bacteria that infects beer. The symptom is a sharp acidic bite to the tongue. Could be caused be poor cleaning of fermenter from last brew. Again, no cure.

Diacetyl Flavour
Often described as butter or butterscotch flavour. Minor lactic acid infection could be a cause. Often from not pitching enough active yeast, Aeration during fermentation, or Transferring to secondary fermenter too soon (absorbed air). Often a buttery flavour can be a characteristic of the yeast being used. Pitching and fermenting at too high a temperature is a cause. Stick to the yeast manufacturers recommended temperatures. If it is the yeast, change your yeast style. If using a lager yeast, cold lager for two weeks at 0-5C, this will reduce some of the diacetyl and the flavour. Curable.

Esters or Fruity Aroma
Esters or fruity, apple like aromas are caused by fermenting at too high a temperature and poor aeration of Wort. Summer temps of 30C + are a frequent cause. Ferment your ales at 17-25C and you wont get fruity flavours or aromas. In Queensland areas, we suggest using a ‘Fridge Temperature Controller’ or placing a large towel over the top of the fermenter with the ends soaking in a tray of water on each side, maintaining a temperature of about 25C with evaporation of the towel, even though the air temperature is in the 30’s. If you taste a sample of the brew before bottling, and it seems to estery or fruity, and you have a fridge available, store the fermenter of beer in the fridge for a couple for weeks at 5C-10C. This helps. It is basically the same as lagering. Even ale yeast will absorb some of the ester & diactetyl flavours. Certain yeasts will provide fruity flavours or apple like flavours. Curable.

Sulphur or Rotten Egg Gas Smell
Sometimes a by product of certain yeasts. Mostly driven off during fermentation. Sometimes a little in bottle. This usually goes in about 30 seconds. The smells that stay are the problem. Can be caused by leaving beer on yeast on itself causing a rotten egg or swamp gas smell. Sometimes it can even produce a burnt rubber smell. If not autolisis, it could be an infection. In either case, good sanitation and healthy yeast are good insurance.
If you are re-using yeast from a previous batch, test it for taste, aroma and appearance. If it tastes clean and beers, smells beery (not sour or acidic) and the colour is pale, light amber to almost white and too dusty in appearance, it is good to use. If it is not good enough to taste, it is not good enough to use. Curable.

Medicinal or Phenolic Flavour (Clove Flavour)
Could be caused by yeast austolsis, bacteria or wild yeast. May also be cause by too much chlorine in water supply. An easy was to get rid of chlorine is to leave a fermenter full of cold water for 24hrs with the lid off. The chlorine will evaporate. Remember though that in wheat beer, the clove flavour and smell is desirable. Curable.

Skunky Odour
We don’t have skunks so we guess an old cat will do for comparison. This smell is from the hops deteriorating in the bottle or the bottles have been exposed to sunlight (ultraviolet) Even fluoro tubes will cause light strike. Store your beer in the dark as long as possible to give a longer shelf life. As little as a week in the light will cause light strike in brown bottles, with green or colourless bottles it will be even less.

There are many other tastes, smells or aromas in beer, several things you should ensure when you are brewing are:

  1. Good hygiene or sanitation will prevent most problems.
  2. Pitching enough yeast for your particular beer recipe will also solve a lot of problems.
  3. Always remember the importance of fermentation temperature!
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