AA% variation - home grown vs commercial

[Matt]

I've been brewing with home grown Pilgrim and the beers are coming out pretty mild - they are coming up like a 5 or 6% AA rather than the 9-12% quoted for the commercial hops. My thought is that the culprit is likely that they weren't dried out enough - does this sound correct?

[scuppeteer]

Quite unlikely that drying is the issue, they are only dried as a preservation method which wouldn't affect the AA% content. As you know soil quality is a major factor for hops, I have noticed up to 2% difference in the same variety depending on where they are grown. Hops from Worcester have had a lower alpha than those from Kent for this seasons crop. All varieties have had lower alpha than 2012 crop due to the weather. Only other thing I can suggest is are you 100% sure its a Pilgrim? I ask as your estimated alpha is considerably lower than any Pilgrim I have ever used.

[guypettigrew]

Not quite, Mr scuppeteer, sorry.

The alpha acid is expressed as a percentage by weight.

The alpha acid is a constant, so the drier the hop the higher the AA%

Guy

[Matt]

Ok, interesting. As Guy states, my thought is that as the cones are slightly 'wetter' the extra weight means less AA going in the wort.

Good point about the variety though Dave, drinking the latest brew again I'm thinking it could be a bit lower still. I got them from Hoads in Sandhurst and they were identified over the phone to me in a bit of a vague way, this was six years ago. I picked them up in the corner of the barn and posted some money through the letterbox

They are pretty neutral indeed with a hint of grapefruit. I should drop the nice people at Hoads a line to ask if they can shed any light on this.

I know it's not that my utilisation is out of whack as non 'Pilgrim' brews are fine.

[scuppeteer]

Not quite, Mr scuppeteer, sorry.

The alpha acid is expressed as a percentage by weight.

The alpha acid is a constant, so the drier the hop the higher the AA%

Guy

I see your point Guy, but why then would there be seasonal variations in AA content when hops must be dried to a minimum moisture content which is 12% or less?
The drier the hop doesn't compute, because high alpha hops generally have a denser cone than low alpha ones; for example Admiral is a dense heavy cone but has a high AA content whereas Bramling cross has a light and quite fragile cone but much lower alpha.

I feel I must contact the Oracle to confirm your suggestions I will report back in due course.

[scuppeteer]

Had a reply from my man in the know, seems we are both right and wrong.

To quote:

"The alpha-acid content varies each season depending on many factors such as: weather, soil temperature, growing and harvesting techniques etc. The measurement of the alpha-acid content also depends, mathematically, on the moisture content because, as a percentage, the greater the proportion that is water in the cone, the lower the relative proportion of alpha-acid. However, in Europe and the UK, the alpha-acid content is usually adjusted and standardised to be expressed as “% at 10% moisture”. Thus, comparison between different alpha-acid contents reduces to seasonal differences.

You do need to take care because it is usual in the southern hemisphere to express alpha-acid content at 0% moisture which, mathematically, gives a higher value. The USA seems to vary in how it expresses alpha content with most using 10% moisture but some 0%. But the USA tends to use spectrophotometric analysis rather than HPLC and spec analyses are always give much higher results. An alpha-acid content at 10% moisture of 16.5% by HPLC will probably give 17.0% by LCV and 18.5% by spec, which would be 20.5% at 0% moisture."


So it would also seem that the way the Americans do it wouldn't give as high AA% if they were analysed in Europe... bloody typical of them to big themselves up!