I'm getting to be a fairly experienced brewer now but this is my first experiment with sours. I read about using lactobacillus from yoghurt so I thought I'd give it a bash.

The process so far... Simple all-grain mash, OG around 1.047. Sparged, raised to 80oC to pasteurise, then chilled to 30oC. Placed in a sanitised demijohn leaving the smallest possible air gap at the top. Just shy of 5 litres in total. Popped a bubble trap on then wrapped it with a heating belt to maintain 35oC. I cannot rule out the presence of oxygen.

I pitched in a 65ml pot of Yakult live yoghurt that apparently contains 6.5 billion lactobacillus casei.

After 12-18 hours there seemed to be gaseous fermentation going on - bubbles rising and a sort of small krausen formed. This puzzled me because I thought casei was homofermentative.

I couldn't resist popping out the bubble trap and having a sniff of the fermentation. Oh dear... I wish I hadn't done that. I was expecting to smell the beginnings of souring... What I actually smelt was an affront to my nostrils... The sort of smell that makes you pull away. Fetid, perhaps slightly fecal, or dead vegetation.

The fermentation appeared to stop after around 30 hours but the smell is still unpleasant. The gravity is still way up near 1.047 so if fermentation as I understand it took place there wasn't much action.

I have risked tasting the product and there is definitely some sourness there, but it's hard to get past the smell.

I'm now in day 3 and the demijohn is just sitting there looking completely inactive... So I sit and wait. It's around pH 3.5.

My plan is to boil the soured wort to drop the break out and kill the lacto, add some late addition hops, and then pitch saccharomyces as normal.

So I guess my questions are...

What is that smell, and is it normal? Will the smell disappear? Will the boil get rid of the smell? If I wasn't going to boil it would be smell disappear? Why did it appear to ferment?

Thanks already for your help! :)

/* EDIT */

I boiled it today, about 3.5 days (80 hours) after first pitch the lactobacillus. There's a strong sourness on the palate but it's not lip-puckering. No bittering hops so it was just a quick 45 minutes boil.

The nasty smell certainly mellowed but didn't disappear completely. It's no longer overpoweringly unpleasant but now just a funky 'note' of the aroma profile.

Steeped 30g First Gold whilst I was chilling it back into a different, sanitised demijohn. Pitched a stack of Nottingham dried for a nice quick fermentation.

/* EDIT */

OK - fermentation over. FG dropped to 1.011 - ABV 4.3%. That hideous smell has mellowed a lot but not completely disappeared. It is still detectable but not unpleasant.

Bottled a week ago but couldn't resist popping a bottle today. Obviously carbonation is poor but it's a lovely refreshing sharpness. On the whole, very pleased. I'll be trying this again.