BREWING
1600
β -Myrcene 585 ppb
Linalool 129 ppb
Static
1400
Dynamic
1200
142 ppb
342 ppb
1000
800
600
136 ppb
310 ppb
400
200
Hop stratication. (Adapted from Barth Haas 2018)
0
0.3
1
3
6
24
on the beer. That said, if a beer with a high nal gravity is heavily dry hopped and packaged unltered, the risk of over carbonation (and explosion) after a few weeks on a warm shelf is real. So, remember to do a risk assess- ment and wear the appropriate PPE next time you handle a can of New England IPA. As well as enzymes, hops also carry with them microbiological passengers from the elds. Whilst they are unlikely to be spoilage organisms, unless added to unpitched wort they will show up on selective media plates looking for wild yeast and aerobic bacteria, leading to insomnia and hair loss in the brewer. Dry hopping with some varieties has been shown to have a deleterious effect on beer foam whereas the use of some varieties actually improved head retention. The diminishing effect is more pronounced at longer con- tact times. Graph 1 shows two hop varieties which improved NIBEM foam stability and two which reduced it. One nal rather astonishing factor is that in large static tanks the com- ponents of hop aroma will stratify. The diagram above represents layering of β -myrcene and linalool in a CCV as measured at Sierra Nevada Brewery.
Dry hopping time (hours)
Graph 2: A comparison of aroma extraction from static and dynamic dry hopping. (Adapted from Barth Haas 2018 )
Some form of tank agitation is therefore required before packaging large tanks of dry hopped beer. Process factors On a process level, dry hopping is dened as a liquid – solid extrac- tion in the case of intact cells and a washing and distribution of free molecules as in the case of ruptured lupulin glands. In both cases avour molecules are moving from an area of high concentration to an area of lower concentration and this process can be described by Fick’s law. That makes it sound very com- plicated but in essence the rate of diffusion of the material in the hop is dependent on how soluble it is in the solvent (beer), the nature of the solvent (ABV, gravity) the concentra- tion of compound in the hop and the beer and how much of the hop is in contact with the beer. All the follow- ing process factors affect the above conditions. • How easy it is to wet and suspend the hop material in the beer
• The particle size distribution of the hop material • Beer temperature • Beer ABV • Movement of hops and beer • Contact time • Oil concentration in hop product used When to add Adding hops at the start of the fermen- tation gives a fruitier, more estery beer and favours the biotransformation of hop aroma compounds. The overall yield of aroma is lower than post fermentation addition and the risk to the microbiologi- cal stability of the beer is greatest. The practice is therefore uncommon. Addition during VDK rest at the end of fermentation provides the best yield of aroma compounds because the beer is still warm (less cold in the case of lager fermentations) and the yeast cell concentration and activity is lower than in fermentation. Additions during lagering (temp <0°C) give the poorest extraction especially if static dry hopping is performed. Dry hop- ping at this stage is the least common.
The ROLEC DH45, ROLEC DH90 and ROLEC DH250 models offer small to large scale breweries a safe and efcient way to dry hop beer
october 2019 I BREWER AND DISTILLER INTERNATIONAL ● 41
i bd.org.uk
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