Hop %aa deterioration rates

[Kev888]

If they're in sealed vac packs and in the freezer i roughly assume a 10% loss in Alpha Acids per year (perhaps 15% if vac packed and just in the fridge), from the harvest date. Seems a bit simplistic though, and some of my packs are getting a bit older than I like (nothing ridiculous, but some are 2009 harvest).

Is it roughly what other people do? Should I calculate the time before purchase differently, for example?

Cheers
kev

[roonikins]

i dont bother assuming a loss at all the hops dont seem to lose there bittering ability they just becomes more mellow with age and less harsh i have been blending old high alpha american hops with new ones and find that the really harsh bitterness that you can get is greatly reduced

[Kev888]

Thats interesting - I think its pretty well established that they do lose over time, but perhaps its the 'real' vs 'perceived' thing raising its head again..

Cheers
Kev

[roonikins]

actually i think it isnt well established at all. the alpha acid is replaced by oxidised beta acid which which supplies more or less the same bitterness but less harshly

[Kev888]

Sigh, another thing that i thought I knew, that I now need to check on then. I seem to be sure of less every time I visit this forum!

I suspect it could well be a perceptual thing then; I know that the measured alpa acids bitterness drop (e.g. here) and personally I've tasted a drop with age that seems to tally nicely with that, but maybe what I'm judging to be less bitter can instead be perceived as just less harsh if its transposed more towards rounded flavours instead.

Sounds not unrelated to the discussions behind first wort hopping, where the measured bitterness doesn't reflect the perceived drop. In fact that may be partly behind my own perception - I tend to do a lot of stuff like first wort hopping, 80c steeping and dry hopping to get a fuller/rounded hop flavour already, so it may seem like the bitterness has reduced if the harsher characters change to become more similar to those.

Time for a bit of research then..

Cheers
kev

[Eadweard]

How quickly hops deteriorate is very variety dependent. I've got a hop book which mentions storage stability. Cascade is 'very poor', Golding 'very good' fuggle 'fair'.

[roonikins]

yeah your right there the more i know it seems the less i know lol.
but to get back to you original question i think at the volumes that we brew at you can more or less ignore loss when you store them like you do.

[Kev888]

You may well be right, with the vac packs and freezer on the go. I've just been doing some reading up, and it seems human perception of differences in bitterness is pretty poor, even by experts and especially in hoppier beers. So unless they're pretty old or have been kept warm and/or unsealed then this may not be especially important in practice.

Just as well really, the %aa figures we start with are only estimates for the harvest, not the particular pack we have - so there again subtleties are perhaps a bit pointless. Think I'll just continue to figure in a small drop per year based simply on my own perception and have done with it, really.

Cheers
Kev