Lacto and IBU's

[gometz]

Lately I have been wondering about how the inhibition of lacto by IBU's is talked about on here. Normally people talk about using only 10-15 IBU worth of hops in their sour beers to avoid inhibiting the lacto activity. But is it the actual converted alpha acids that inhibit lacto?

As in, if you add half an ounce of Saaz at 60 minutes compared to two at 15 minutes and assuming the IBU's are the same; is it the same level of inhibition, or four times?

As I understand it, hops themselves have preservative qualities, not brought out by isomerization of the alpha acids. By talking strictly in terms of IBU's is it assumed you are only doing early additions?

As background: I am making (or trying to) my first sour using 3203 and used 0.75 oz of Nelson Sauvin in the last minute (trying to only get aroma). But now I realize I may have killed the bugs and I'm a bit worried. Others seems to be getting a noticeable sourness after a week using 3203, but mine is barely if at all noticeable.

 

[ArcaneXor]

Doing a quick lit search for abstracts, it does seem like it's the hop acids that inhibit some Lactobacillus strains.

 

[TopherM]

If you are only looking for aroma, complete your lacto souring, then just do a strong dryhop prior to packaging/serving. Then your lacto and your hops never interact.

 

[gometz]

If you are only looking for aroma, complete your lacto souring, then just do a strong dryhop prior to packaging/serving. Then your lacto and your hops never interact.

This is my plan from here on out, but now I am just worried that I've killed my lacto. I think I am going to pull a sample, purge it with CO2 and place it in a warm water bath in a cooler at about 100*F for a day or two to see if it sours quickly.

 

[metic]

As I understand it, its not just alpha acids/IBUs that inhibit lactobacillus. Lambic producers use large quantities of aged hops in which alpha acids have degraded.

That said, adding 20 grams of late boil hops isn't going to wipe out the lactobacillus. (In fact, I'm not sure that hops kill lactobacillus so much as slow down its reproduction.) So maybe the bugs were outpaced by the saccharomyces in the blend. The effect that has will depend on how much fermentable sugar is left in the wort after primary fermentation. It might mean that the beer takes longer to sour (if there is enough sugar left for the lactobacillus), or it might mean that it doesn't get quite as sour as you'd like (if there aren't enough available sugars, or if alcohol levels get high enough to kill of the lactobacillus before they've made their contribution).

But if you're only seven days in, I'd wait at least another week or two before getting worried. Its too early to tell---my berliner weisses are only a little tart after a week, but plenty sour after a month or two.

 

[youreanimpulse]

I am using 3203 on an Oud Bruin and just tested it at four weeks. Same gravity as two week test: 1.012 from 1.05. Slightly more sour than at two weeks, which is still not very sour. It seems like it's working slowly but not that slowly (compared to other sour mixes I've used). I have mine at 9 IBUs, all at beginning of boil. If yours is souring within a week or two I think you're on the right track. But only time will tell. If it stops souring before you want, add pedio and wait a while.

 

[gometz]

I need to take a gravity sample today, but the last one was not very if at all sour (that was on Thursday, 6 days in).

 

[youreanimpulse]

Yeah, I checked at two weeks, so I guess I can't comment. Seems early for worry. I wouldn't sample yet if it were me. They say 6-8 weeks for this mix to sour completely, and I assume that's if you aerate as suggested, which I won't except for opening for sampling biweekly (much more often than I would normally, it's supposed to be fast, so I want to observe it). I'll be happy if it's 3 months, still plenty fast for a sour.

 

[gometz]

Yeah, I checked at two weeks, so I guess I can't comment. Seems early for worry. I wouldn't sample yet if it were me. They say 6-8 weeks for this mix to sour completely, and I assume that's if you aerate as suggested, which I won't except for opening for sampling biweekly (much more often than I would normally, it's supposed to be fast, so I want to observe it). I'll be happy if it's 3 months, still plenty fast for a sour.

I guess normally I wouldn't worry, but seeing everyone else come out saying that they were getting sourness so quickly made me worried. I am going to buy another pack to make another sour later on, but I guess with this one I will wait and see what it does over the next month. I'm 10 days in now, it has been sitting at above 80*F most of the time, so I guess I'll see what I get. No idea what the sacc strain in there is.

 

[youreanimpulse]

Yeah, hard to tell about the yeast. I'm not getting a ton of yeast character that I recognize. It looked like a couple Brett primaries I have done, and I believe some form of Brett is confirmed to be in this (and not in the Oud Bruin). The neutral phenolic/fruity ester nature of my taste tests also reminded me of my previous Brett primaries at this stage, but it isn't as thin (which may be partly my grist and mash schedule). Interesting stuff. So far it's playing well with the dark grist. Good luck, I'm sure it'll be tasty!