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ryane
08/12/10 02:21 PM  
Brett and Lactic acid
On another board the topic of brett and lactic acid production came up. As far as Ive read brett can produce acetic acid, but Ive never come across anyone else claiming it produces lactic acid

so my question is, will brett produce lactic acid?

ChadYak
08/12/10 03:11 PM  
Re: Brett and Lactic acid
From everything I've observed and read it will produce some lactic acid through various metabolic processes but the levels excreted into the medium are low, maybe 1-10 mg/l depending on the specific strain and environmental conditions.
ryane
08/12/10 05:59 PM  
Re: Brett and Lactic acid
have any of the sources that i can look at?

Ive also come across that the taste threshold for lactic acid is in the neighborhood of 400ppm, any comments on that?

it would seem that there would be no noticeable impact on flavor from that low of a level produced

brewinhard
08/13/10 09:07 AM  
Re: Brett and Lactic acid
Check out Chad Y's Brettanomyces Master Project! Great info and more than you ever wanted to know on these crazy critters!
ryane
08/13/10 11:40 AM  
Re: Brett and Lactic acid
brewinhard - I did, I searched the entire site, but not much info on lactic acid, Im hoping that he can send me some links/references as Id really like to read about this....
CHadYak
08/14/10 02:07 PM  
Re: Brett and Lactic acid
ryane, there is no direct texts which talk about lactic acid production. The main acids produced and transported out of the cells are acetic acid, capric acid, caproic acid and caprylic acid. The reason nothing exists on lactic acid is because it doesn't produce it in quantities that have any organoleptic impact. Most strains most likely form almost none. Acetic acid on the other hand is heavily produced in aerobic environments, and therefore has been heavily concentrated on in previous studies. How most of the studies concerning compounds with yeast occur is through observing esters and then looking at the production of the acid which made up part of that ester and looking for its origin. If Brettanomyces species produced lactic acid, it would have been written about academically already, but instead it has been shown that without exogenous additions of lactic acid, minute amounts of ethyl lactate are formed if at all.

In my study I observed ethyl lactate production in every fermentation. All the fermentations which observed pitching rate and no lactic acid addition had between .18 and 1.81 mg/l. When adding 100 mg/l between a 5 and 10 fold increase in ethyl lactate was observed. This trend continued all the way up to 3,000 mg/l which I observed too.

That data is what leads me to believe somewhere between 1 and 10 mg/l is excreted out of the cell during various metabolic processes. If you go and read up about the TCA cycle and then read about the activity of the EMP pathway in Brett and lowered amino acid synthesis during aerobic growth a spotty conclusion can be made that somewhere some is being produced through various steps and not fully consumed. But Brett does not lactic ferment, this is a whole different process, and as those pathways do not appear to exist in the genome and they have not been observed by previous researchers. Lactic acid is not produces by Brettanomyces the way a lactic ferment takes place in Lactic acid bacterias.

All this will be up on the site soon and you can read all about various pathways and secondary metabolites. But it takes time to get content up and converted for the web.

ryane
08/14/10 05:42 PM  
Re: Brett and Lactic acid
thanks for the extra info, I searched and searched and could not find much info on lactic acid and brett in literature, and I suspected that if anything any discussion would be related to the krebs cycle and no actual production would be evident

the reason I asked was that someone had stubbornly refused to believe that brett did not produce lactic acid in a way that was appreciable, and they cited a ppt by steve piatz (hb assc) that stated brett produced lactic acid, I disagreed but they wouldnt believe me

ppt if your interested, its slide 19

http://www.homebrewersassociation.org/attachments/0000/4959/Sour_Belgian_Talk-Steve_Piatz.pdf

ChadYak
08/15/10 01:03 AM  
Re: Brett and Lactic acid
Yeah, most of what he has on there is spot on after a quick look over. Steve probably mistook something someone said one time. Krebs cycle (TCA cycle) that would be the place I would suspect any excess lactic acid would be made. This is different then a lactic acid fermentation.. which I'm not sure if any yeast is capable of.. anyone know of a yeast which produces lactic acid?
 
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