Interesting study on effects of dry hopping rate

[ChristinaS1]

In another thread (on the effects of whirlpool additions) we touched on the subject of oxidized alpha acids, aka humuliones, which are 2/3 as bitter as iso-alpha acids. Because they are highly soluble, even at fermentation temperature, they can result in more bitterness than expected from whirlpool and dry hop additions, particularly if the hops are not super fresh. As we are all aware, brewing software does not address dry hopping. Today I came across this study, which actually touches on this:

https://www.researchgate.net/publication/326992316_Impact_of_static_dry-hopping_rate_on_the_sensory_and_analytical_profiles_of_beer

Figure 4 shows how many IBUs are added at different dry hopping rates; these IBUs come mainly from humuliones, but there is some contribution from other factors. The graph is a small and a bit hard to read, but from what I can see:

2gm/L adds ~2.5IBUs

4gm/L adds ~3.5IBUs

8gm/L adds ~6.5IBUs

16gm/L adds ~8IBUs

The study covers many other interesting things as well (ie., that DH above 8gm/L actually leads to the suppression of citrus flavours, by herbal / tea flavours); I highly recommend reading it. 

Cheers,

Christina.

[The Captain!!]

 Nice one Christina. 

I honestly don’t think the world will be that far off a bitterness measurement for whirlpool and dry hop additions of non isomerised hop matter. 

Which I believe will help the consumer with their choices on the beer that they prefer. 

[BlackSands]

2 - 8g / litre is the usual range of dry-hops most would use I image.   In this range the relatively few extra IBU's produced are probably well within the margin of error for software IBU estimations anyway so I'm therefore wondering if it's really something we need concern ourselves with?      

Quote

...brewing software does not address dry hopping

Nor does it address the effects of storage method and age on the hops AA's etc.  These are hard to account for and therefore that alone surely makes the whole idea of calculating IBU as little more than mere guesswork, unless you're using hops that are freshly tested straight from the farm!?   

[Otto Von Blotto]

Beersmith has a hop storage index function, I haven't really played around with it yet though to see how it might work. 

[BlackSands]

36 minutes ago, Otto Von Blotto said:

Beersmith has a hop storage index function, I haven't really played around with it yet though to see how it might work. 

Ah, yes...   you're right, though curiously it seems it calculate far less AA% loss than other online tools I've used.  However the problem is knowing the actual history of the hops you buy from your LHBS in the first place.   No store here that I know of dates their hops, and many have less than ideal storage and I certainly don't know the storage temperature of my LHBS's hop fridge.   

My real point here is that the unknown amount of IBU's lost with aged hops along with other variables that seem to drastically effect the accuracy of IBU caculations far outweigh the small IBU increase associated with dry-hopping.   

[ChristinaS1]

You are right that the numbers in that chart are small. I read once that we can't distinguish between two beers unless the IBUs are more than 5IBU apart, so maybe it we can ignore it.  On the other hand, I kind of doubt the people doing the study got their hops from the LHBS down the street. I assume mine are less fresh, which could bump the number of IBUs above the taste threshold....But maybe not at the rate I dry hop. 

Cheers,

Christina.

[Otto Von Blotto]

It probably assumes hops are stored properly vacuum sealed in a freezer. I buy my hops from Yakima valley which I know stores them properly, however they'd be at ambient temperature during the time it takes to get here from there. Once I get them though they're straight in the freezer. 

Whether or not the alpha percentage has dropped, I turn out beers as expected so I haven't really paid much attention to the HSI. Maybe with older hops but usually they don't last more than a few months.