Sterile Techniques

The elimination of contamination is the most important factor in brewing; the one a brewer cannot afford to get wrong.

No matter how good the recipe, how efficient the mashing, how high the quality of ingredients, if the brew is contaminated it’s all for nothing. Poor sterile technique is the one factor that can undermine all the others and ruin a lot of hard work. The only microorganism in your beer should be the fermenting yeast. If only this were always so.



May sound obvious, after all, we know when a pint is off, but I believe that contamination can be quite insidious. What about lower levels of contaminants that, while not sufficient to be seen as such, are manifested as a taste that lacks the ‘usual flavour’, or is an ‘average pint’, or ‘nothing special?’ Its easy to put it down to a poor mash or recipe, but it might also be that some contamination got in between sterilising and using the fermenter bin, or before a vigorous fermentation got going – especially if there was a long cooling period, and was the wort boiled soon after mashing? Boiling may destroy any contaminants, but even dead bacteria and the compounds they produced while the wort was sitting at cool temperatures, might still taint the brew.


The essence of good sterile technique is to minimise the opportunity for contamination and incubation. Always use equipment as soon as sterilised on the assumption that something will always get into containers and onto stirrers etc. as soon as they are free of sterilant. We all have our own sterile methods and each considers their’s to be fine or wouldn’t use it. However it is likely that we all have our own ‘lazy moments’ or ‘blind spots’ as well as sound methodology, which it is important to share, and is why I want to start a discussion on sterile techniques.

An illustration – albeit from an absolute beginner. [Anecdote about beginner who dried sterilised bin with dishcloth].

Brewing equipment has to be microbiologically clean, not the same thing as just physically clean.

I repeat, sterility is the most important factor in producing a good beer. In fact I would say that the drop in quality due to contamination off tastes is likely to be greater than the gain in quality from full mash brewing. Anyone noticing off tastes should put on a kit or use malt extract. Any problems with mashing can then be eliminated. If there are still off tastes, there is a sterility problem and one may just as well stay with kits until it is sorted out.


I use Sodium Metabisulphite, which does not need to be rinsed, unless dirty, then Chempro. There are equivalents eg. bleach (1 cup per gal.). Don’t forget boiling water, always have a kettle handy for a sterile rinse and emergencies.


Have a large bowl into which will fit the largest utensil. Addis make good square bowls with close-fitted lids. All utensils that will make contact with the wort or sterile surfaces are kept submerged in sodium met. in the bowl with lid fitted, until used, then returned. This includes stirrers, thermometer, hydrometer, funnels etc. and tubing (get all air out). Sod. met. does not need rinsing off, but if using Chempro or bleach (why?) utensils can be rinsed with boiled water before use. Do not just sterilise utensils once, then leave them on the draining board etc. to gather bugs.


Microorganisms and spores are falling out of the air constantly and will rapidly contaminate any exposed surface. Anyone who has studied microbiology will have done the experiment exposing agar plates for 30sec, 1, 2, 5, 10 min. etc and incubating. This gives a frightening measure of the rate of microbial ‘fall-out.’ Sterile surfaces must be kept covered. Keep the lid on the fermenting bin with sterilant in until it is used. Only remove the lid to empty sterilant and put in wort and water and then replace the lid. Wort can be stirred by lifting the lid on one side only with a sterile spoon left inside until the yeast has been pitched. Then clip the lid 2/3 around the fermenter, just enough to allow excess CO2 out and cover with a towel. Resist the temptation to keep lifting the lid every day or so to see how its doing, only open when necessary eg. skimming, stuck fermentation etc. In the home, contamination cannot be eliminated, only minimised.

Do the same with barrels. A spare barrel cap with the valve hole sealed with tape can be used while sterilising, to prevent sterilant damaging the valve of the valve cap. After filling the barrel, the valve cap can be sterilised with boiling water.


is removed from the bowl and emptied of sterilant and fitted into bin and barrel without it touching anything else. A sterile short piece of tube can be fitted to the siphon end and used to suck on and removed as liquid starts to flow down. This avoids putting your mouth on the siphon tubing.


Bottles are cleaned and sterilised by 1/2 filling with fresh sod. met. Eight are filled, sealed and left for 20+ minutes. Then emptied into 8 more bottles and left to drain. I have one batch sterilising, one draining and one being filled. In this way the same 4 pints of sod. met. can be used to sterilise 40 pint bottles. Before filling, the drained bottles have caps removed and are shaken to remove excess sod. met. I use a conditioning tank with a Boots flip-top spout (sadly no longer available) which fits into the bottle.



is from a clean batch. Do not use sugar from the general household stock. Buy a fresh bag of cane sugar and keep sealed or in a sterilised jar with a label threatening anyone who touches it, puts wet coffee spoons etc. in it, with death, or worse. Better still, keep the jar under lock and key and labelled potassium cyanide.’

After being careful thus far, you do not want to add contamination at the final bottling stage. The sugar bag or jar is kept on its side to prevent ‘fall-out’ getting in. A teaspoon is sterilised with boiling water (which evaporates) and kept under a clean, folded kitchen towel at all times when not being used to transfer sugar.

A plastic funnel is sterilised inside and outside with boiling water, fitted in a bottle and sugar added. Once some beer has washed the sugar in, the funnel is removed and the bottle is filled with the tap nozzle. The funnel is inverted and left to drain on kitchen paper. Every 8 bottles the funnel is re-sterilised.


Put hops in a muslin bag and place in small saucepan. Add priming sugar and just cover with boiling water. Simmer briefly. In this way hops and sugar are sterilised together before adding, with water, to the barrel or conditioning tank.



  1. Sterility is the most important factor in brewing, sincecontamination can undermine everything else.
  2. Low level contamination, not necessarily perceived as such, can makea potentially great beer, mediocre.
  3. We can’t eliminate contamination, only minimise the opportunitiesfor infection and incubation.
  4. Sterilise every container and utensil that will touch the wort.
  5. Use wort and equipment immediately after sterilisation, they won’tstay sterile.
  6. Do not allow anything non-sterilised to touch sterilised equipment.
  7. Sterilise with sodium metabisulphite solution, which does not needrising and helps preserve beer, or with chlorine-based products such asChempro or bleach which do. Don’t forget boiling water, always have

    some to hand.

  8. Sodium met. only sterilises. Use Chempro, bleach etc. to clean andto remove the few contaminants against which sodium met. is lesseffective.
  9. Keep utensils submerged in Sodium met. in a bowl with a lid, betweenuse.
  10. Keep the lid on fermenting bin and barrel between sterilising andfilling, stirring etc.
  11. Put a few pints of sodium met. solution into sealed barrels, binsetc during storage to prevent mould.
  12. Buy a spare barrel cap (with hole covered with Sellotape etc.) touse during sterilisation and storage as sterilants corrode the valve.Sterilise valve cap with boiling water.
  13. A rapid start to fermentation reduces contaminant growth. Use anactive yeast culture or pitch dried yeast at 80oF/27oC.
  14. Clip the bin lid 3/4 around and cover bin with a towel or blanket.Only lift lid when necessary eg. to skim yeast, check gravity.
  15. Submerge siphon tubing carefully to fill the inside with sterilant.
  16. To start siphoning, use a sterilised 5ml auto pipette tip, shortpiece of tube etc. to attach to the end of the siphon to avoid touchingit with your mouth.
  17. Sterilise 8 bottles with half a pint of sodium met. for 15-20 min.Then pour into the next 8. In this way 4 pints sterilises 40 pintbottles.
  18. Priming sugar should be kept purely for brewing and separate fromthe household supply. Dispense from a container on its side or coveredagainst “aerial fall-out.”
  19. Regularly sterilise spoons and funnels for putting sugar intobottles during bottling.
  20. For dry hopping, put hops in a muslin bag and blanche in a minimumof boiling water and add water with hop bag to barrel, conditioning tanketc.

Robin Jones

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