Old hops

[nman13]

Forgot to order hops and brewing my first sour tomorrow. Found some old cascade hops in the fridge (~1.5 years old if I had to guess) that were open and in a ziplock bag, 4.9% AA. I know aged hops are traditionally used in sours. Thoughts on what to do? Not near any LHBS. Any best guesses on what the AA for these hops is at now?

 

[RPh_Guy]

Unless you have very robust lactic acid bacteria that you need to knock down (I'm guessing not), I'd suggest using about 0.2-0.4 oz per 5 gallons @60min.

Cheers!

 

[sweetcell]

another alternative would be to add hops at the end of the boil. there are several reasons why hops are used in sours, one is that brett interacts with hop compounds to produce flavors. adding hops late in the game will allow you to add more without adding too many IBUs.

 

[RPh_Guy]

If I'm not mistaken, it's the hop quantity, and not just the isomerized alpha acids that inhibit the LAB. For example, a dry-hopped beer with no isomerization will still inhibit hop-sensitive LAB.
IBU is commonly (mistakenly) used as a surrogate for hop quantity, which causes confusion on this issue.

Belgian brewers use ultra-low alpha acid hops so they can use a high enough quantity to inhibit their aggressive LAB without adding too much bitterness.

I believe the extra compounds for Brett to utilize are a beneficial side effect of that process, but not the primary goal, otherwise they would dry hop to avoid lots of the aromatic compounds being driven off during the boil (as you suggested).

Cheers

 

[Vale71]

As actual hop material always gets removed from beer the anti-microbial action is necessarily due to hop constituents that are left in solution in beer. In the case of lactos it's the alpha-acids that inhibit their growth. It's actually irrelevant whether they are isomerized or not as isomerization only affects solubility in water, but as solubility of non-isomerized alpha-acids decreases sharply with decreasing PH-value there won't be much non-isomerized alpha-acids in a sour beer, so isomerization is actually necessary.
At normal beer PH there is a non trivial amount of non-isomerized acids in solution, that's why lab measurement if IBU values actually measures total alpha-acids regardless of isomerization state.

Edit: as a matter of fact, some studies suggest that the non-isomerized form actually has a much stronger bacteriostatic action.

 

[RPh_Guy]

Down the rabbit hole we go. So much for the simple suggestion to the OP
By the way, that recommendation is based not only on my own limited experience, but also known hopping rates for a variety of commercial sour breweries using aged hops.

Moving on...
The point I'm trying to make: calculated IBU is not a great marker for antimicrobial-activity vs the amount of hops used in the beer.

It sounds like you might be disagreeing or not understanding what I said. I'm not sure, so I'll explain further.
IBU is calculated based solely on isomerization of alpha acids, yes?

Alpha acids are not the only anti-bacterial compound in hops. Other compounds in hops do have a strong effect, including oxidized beta acids (particularly significant in aged hops), polyphenols, and essential oils, none of which are included in the IBU calculation.

Dry hopping is known to inhibit souring. IBU calculations simply don't explain this.
http://www.milkthefunk.com/wiki/Hops#Dry_Hopping
Anecdotally, as little as 4 grams of dry hop per gallon immediately stops L. plantarum metabolism (also indicating that the hop activity is not reduced at low pH).
It follows that IBU calculations from late kettle additions will be similarly useless for estimating the antibacterial effect of the hop amount used.

At normal beer pH there is a non trivial amount of non-isomerized acids in solution,
[...]
as a matter of fact, some studies suggest that the non-isomerized form actually has a much stronger bacteriostatic action.

Agreed, this also proves my point. IBU calculations only account for the isomerized alpha acids.

Would a lab measurement of IBU provide a better predictor of the antimicrobial activity of a hop addition? Probably, but do home brewers have easy access to that? Obviously not yet.