Quick question for the group: Will unsanitized priming tablets/sugar likely/surely cause off flavours after bottle conditioning - especially, a wet/slightly moldy towel aroma?

I've been experiencing this off aroma/flavour consistently after bottle conditioning - and it's NOT present out of the fermentor (tastes excellent initially). Fairly sure my AG process is decent, sanitary, and it's not a yeast or ferment temp problem. Newbie question, but I've been using Cooper's dextrose tablets, and/or white sugar added directly to the bottles for priming. For my latest batch I boiled white sugar and primed in a bottling bucket as per traditional method - and I tasted a bottle after a week, and it was amazing - with no off flavours (yet;), and on par with what I would have expected out of the fermentor. I'm hoping this is the answer but wanted to ask for advice.

Does anyone have experience with this? And other than my so far anectodal experience, is it a no brainer that you must sanitize priming sugar - even those priming tablets?

Thanks a million for any and all help.

  • Can you describe that off aroma / off flavor?
    – Robert
    Jul 27, 2016 at 14:46
  • Hard to pinpoint but closest I can guess is "cardboard", but I can't really say for sure, but it isn't skunky, sour, or DMS-like. Another thing that happens is the body gets sweeter and develops a caramelly kind of flavour that wasn't initially present. I've heard this can be common with oxidation? I've since been boiling my priming sugar so fairly certain it isn't from that. I replaced my autosiphon as I'd also found a crack in the body of the large sleeve and checking or small cracking in the smaller rack insert part...
    – A. Mason
    Jul 28, 2016 at 13:52

3 Answers 3


I usually dissolve my sugar in boiling water, before adding it to the bottle or kegs for priming.

I have in the past just added half a spoonful of granulated sugar directly to the bottles with no ill effects.

If you are worried this may be a source of your off flavours then make a sugar syrup, and boil it for 15 min, then allow to cool with a lid on, and use this sterile solution to prime your bottles. Then at least you can rule out this as a source of contamination.

I would be surprised if this is your source of a mildew like mouldy smell, but best to be able to rule it out and then work down other possible avenues.

Tips for avoiding musty off flavours:


I have a couple of questions:

  • Where are you storing your tablets/priming sugar?
  • Where are you storing your bottles once filled?
  • How are you sanitising your bottles and caps?

If you are storing your beer/tablets in a dark musty environment then the chance for cross contamination is high, humans threshold for the musty chemical 2,4,6,trichloroanisole (TCA) is about 25 parts per billion. So the slightest contamination from the environment will affect your enjoyment of your beer.

Also, make sure you're thoroughly sanitising your bottles and caps, as the slightest pick up of mold will linger in the bottles during conditioning and metabolise chlorinated phenols in your beer into TCA. Pre-boiling your tap water before making the wort will help drive off the chlorine from the tap water which may reduce the amount of chlorinated phenols for the mold to convert.

Sanitation is most likely the problem, at some point somewhere you are picking up some mold, or you have been storing your products/finished beer in a moldy environment.

I had a similar problem, when I had been storing my beer our cellar, which can get a damp floor. I stopped storing my boxes of beer on the floor of the cellar, by building some shelves, which allowed air to flow around the floor and keep it dry and kept the cardboard away from the damp/condensation. This solved my problem.


In a word, no. What you are experiencing has another cause.


I have never had problems adding dextrose or sucrose directly in powder form to bottles. It can be messy but I have not found it to cause "bad bottled beer". Obviously I have never used any "suspect"/old/discoloured sugar so I don't know if they cause problems.

I would tend to recommend dissolving the priming sugar in boiled water, adding it to a suitable size bucket/barrel and pouring (siphonng if faint hearted) the beer to mix it uniformly - then bottling. As the original post shows - this produces good carbonated beer without all the hassle of spooning (and spilling).

  • Thanks for the response. I have since started boiling the priming sugar. So do you pour your beer from fermenter into the bottling bucket and not siphon?
    – A. Mason
    Jul 28, 2016 at 13:54
  • Yes I pour from bucket to bucket "in air". This is not generally regarded as good practice - allegedly due to oxygenation or infection. I discount oxigenation as a source of problems (for me anyway) but I accept that in some environments pouring may not be an optimal transfer method. But I use it and it works well for me. Actually I pour off the trub to allow clearing and then after a few days I pour the cleared beer onto the priming solution. Lots of foam and swooshing beer. If worried by pouring one can always siphon the beer onto the priming solution. Jul 29, 2016 at 16:11

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