Help me understand IBUs in Sours

[Calder]

Berliner Weisse has less than 8 IBUs. Lactobacillus has little tolerance for hops.

Lambic/Gueuze has less than 10 IBUs. Basically made with old hops. Above 10 IBUs Lactobacillus can be inhibited. Pedio can also be inhibited at this level.

Flanders Red has 10 to 25 IBUs (per BJCP guidelines).

If we keep IBUs low in Lambics to enable the bugs, why are higher IBUs OK in Flanders Red when they basically use the same bugs?

 

[metic]

Well, according to Jeff Sparrow in Wild Brews, Rodenbach is only hopped to 8-10 IBU. So I think it varies:

Some traditional Flanders beers are hopped at a low level (10 IBUs) to allow Lactobacillus (and Pediococcus) to reproduce more freely. Other Flanders beers may be hopped to a much higher degree yet still exhibit a characteristic acidity. Remeber, resistance to hop acids depends on the particular species, and sometimes even strain, of gram-positive bacteria.

Pediococcus should be fine above 10 IBUs, and even lactobacillus I think, if there are sufficient sugars left in the wort by the time they've reproduced enough to be a factor. The hops slow them down, but they don't necessarily halt them as soon as the IBUs are above 10. With a Berlinerweisse, you want a lot of activity from the lacto earlier on, before all the sugars are consumed by yeast, so you want to keep hop level minimal to encourage fast growth. With other sours (like Russian River), the majority of the acidity comes from the pedio rather than the lacto, and doesn't really show up until later stages in the fermentation. So a) slow reproduction by the pedio isn't necessarily a problem (it's always pretty slow, as I understand it) and b) IBU levels will have dropped by that point anyway.

 

[40watt]

Exactly. It really the American examples that are a bit higher.
In addition to what metic said, notice that many times if a higher hopped sour is produced in a shorter period of time, it's because a very acidic stock sour has been blended with a young hoppy beer.

 

[metic]

Lambic/Gueuze has less than 10 IBUs. Basically made with old hops. Above 10 IBUs Lactobacillus can be inhibited. Pedio can also be inhibited at this level.

Something that caught my eye as I was flicking through Wild Brews tonight:

Lambic brewers realize that, while aged hops have lost their ability to contribute bitterness to wort, they have not lost their preservative capabilities. Two other compounds---beta acids and polyphenols---do not suffer any notable affects (in context) from aging and oxidation. The beta acids contained in hops also have a powerful antibacterial effect against the growth of thermophilic gram-positive lactic acid-producing bacteria, namely those of the genus Lactobacillus. (Lactobacillus, therefore, plays virtually no role in lambic fermentation. Pediococcus damnosus produces most of the lactic acid.) p.129

So in other words, it's not necessarily the alpha acids responsible for bittering that inhibit lacto; so it would be wrong to conclude that the low IBUs in lambic are to facilitate acid-production by lactobacillus.

 

[dantheman13]

I heard a recent talk on hops where the presenter said that "beta acids kill bacteria", and thought to myself, "no it's the alpha acids!" I did some Google searching and found a few resources (other than Sparrows) that backs that both alpha and beta acids have some hindering effect on gram-positive bacteria:

http://bioweb.uwlax.edu/bio203/s200...ommon Hops/Hop Anatomy and Chemistry 101.html (search for 'antiseptic').

http://people.westminstercollege.ed...CH/Fundamentals of beer and hop chemistry.doc (search 'bacteria')

There are quite a few more references out there.

 

[Oldsock]

Hops are really only required (in terms of process) when you are doing a coolship-style spontaneous fermentation. Without them the Lactobacillus can get rolling too quickly, causing problems for the wild Saccharomyces. Aged hops are used because they contribute enough anti-microbial compounds without imparting excessive bitterness. Oxidized beta acids do contribute bitterness, but it's unclear exactly how it compares flavor-wise (or in terms of persistence) with iso-alpha-acids.

I add 10-15 IBUs to most of my sours out of habit, and haven't had a problem souring. By the time the beer is ready to drink, bitterness is well below the flavor threshold. There may be some subtle flavors contributed by hops, either fresh or aged, as their compounds are acted upon by Brett and the other microbes.

 

[tgmartin000]

Hops are really only required (in terms of process) when you are doing a coolship-style spontaneous fermentation. Without them the Lactobacillus can get rolling too quickly, causing problems for the wild Saccharomyces. Aged hops are used because they contribute enough anti-microbial compounds without imparting excessive bitterness. Oxidized beta acids do contribute bitterness, but it's unclear exactly how it compares flavor-wise (or in terms of persistence) with iso-alpha-acids.

I add 10-15 IBUs to most of my sours out of habit, and haven't had a problem souring. By the time the beer is ready to drink, bitterness is well below the flavor threshold. There may be some subtle flavors contributed by hops, either fresh or aged, as their compounds are acted upon by Brett and the other microbes.

Hey Mike, pre-ordered your book the other day - can't wait!

So you bitter a beer to 15 IBU and still get good results using lacto D?

 

[Oldsock]

Hey Mike, pre-ordered your book the other day - can't wait!

So you bitter a beer to 15 IBU and still get good results using lacto D?

Most of my sours have Pedio in them. If you are relying on commercial Lacto alone, I wouldn't go over ~5 IBUs.

Cheers, enjoy... eventually!