Does dry hopping produce gas? (not hop creep)

[hoppyscotty]

In my last two brews, the second of which is in the fermenter now, I've taken to dry hopping via a hop drop after fermentation has completed (three or so days of stable gravity reading) and sealing off the fermenter for the dry hop period.

In my last brew I noticed the pressure in the vessel had increased and continued to increase to quite a high pressure - think I caught it at about 18psi. I checked and sure enough I had some hop creep with the fermentation kicking off and dropping a couple of points or so. so that explained that. No harm done and the beer was delicious...probably the best I've ever brewed.

In this brew I dry hopped yesterday in the same way and monitored the gravity (iSpindel) looking for signs of hop creep and no sign of any gravity change. However checking earlier today and I was at 10psi.

I have full temp control and the temp of 15 degrees C has been maintained within a degree, so not expansion due to temperature, and no signs of hop creep and off-gassing due to further fermentation (probably need to double check with a hydrometer just in case). So leads me to a question about hops off gassing even without further fermentation? Anyone else observed this??

Thanks

 

[Rwilts]

I ferment under pressure and when I dry hop pressure builds back up well after fermentation has stopped. I presume the hops cause Co2 to come out of suspension,

 

[Jim Brewster]

Nucleation

 

[chthon]

I don't think this can be attributed to CO2 coming out of solution. The amount of CO2 dissolved is a function of temperature and external pressure, and would be in equilibrium. If temperature dropped, more CO2 would dissolve and you would get underpressure, if temperature rises, CO2 would come out of solution and pressure could rise. However, there is also external pressure to take into account. If external pressure rises or falls, the amount of CO2 in solution would also change with that.

However, you do not need much fermentation going on to generate CO2. Every 4 gram of sugar fermented gives around 1l of CO2. And this is a reaction that does not have an equilibrium. You won't measure the reduction of these small amounts of sugar with the hydrometer. Most of them have a scale of 0.002, which amounts to appr. 0,5 gram sugar per litre of liquid.

So I think that this pressure build up is because of residual fermentation.

 

[foxy]

It is residual fermentation as chthon suggests, why, the amyololytic enzymes in the hops converting non fermentable dextrins into fermentable sugar, but probably not enough to register on a hydrometer reading.

 

[hoppyscotty]

Ok. Makes more sense as I didn’t ferment under pressure and only closed off the tank once I had dry hopped. I wondered if it was hop oils vaporising or something daft like that. Quite handy actually for enabling remote cold crashing without worrying about suck back and self carbonation. I’ll take another hydrometer reading as I guess my ispindel could be out of whack after having a few hundred grams of hops dropped on it.

 

[moto748]

I dry-hop my parsnip stout (funnily enough, I don't usuallt bother with 'proper' beers). Anyway, I dangle a thin muslin bag of hops into the demi-john, the bag clamped in position by the air-lock bung. Typically I do this when fermentation has about finished, and gravity is about 1009-1010. Always this produces some action on the surface, and the air-lock starts up again. After three or four days, it's subsided, but gravity has gone down to 1005-1006, and ready to bottle.

So yeah, for me, that is proper fermenatation. And a good thing, although attempts to replicate this with 'proper' brews have beem more variable.

 

[The Baron]

Yes Knew I had read it somewhere
The enzymes in your dry hops have acted upon the starches and dextrins in your beer, breaking them down into fermentable sugars. The yeast that you have left in your beer has refermented those sugars. Yes, it's a secondary fermentation

 

[Agentgonzo]

The dried hops are small and compressed. After a bit if a soak in your beer, they will absorb water and swell up. It's possible that the volume of hop cells/fibres take up more volume once they have absorbed the beer and swelled up than the original volume of the dry hop matter and the beer-that-gets-absorbed. I have no idea whether it does or not, but it could be another reason for an increase in pressure/airlock bubbling

 

[hoppyscotty]

Yeah could be increase in volume of soaked hops. It was a large hop charge and I did seal the fermenter after adding them. I did see a drop in FG in my first batch so put it down to hop creep, but not in this second which is what confused me - maybe it was only a point or two drop so not detectable on my hydrometer. A handy thing anyway as it carbonated my beer for me so saved on CO2.

 

[Agentgonzo]

IIRC a drop in gravity by two points produces a volume of CO2. So a negligible drop in gravity can still produce a significant amount of CO2 to raise the pressure