This week I look at some of the advantages and disadvantages of whirlpool hopping in an effort to better understand the technique.
Whirlpool vs Dry Hopping vs Boil Hops
Its important that we start with a short discussion of the three major hop methods. Most brewers are familiar with boil hops, which are primarily used to add bitterness to the beer. Whirlpool and dry hops are not added for bitterness, but instead are used to preserve delicate aroma oils and flavors. Whirlpool hops are added at the end of the boil at temperatures below boiling and typically steeped for a period of time from a few minutes to as long as an hour. Dry hops are added during active fermentation or in the secondary.
In the simplest form, we use whirlpool hops and dry hops in an effort to force aromatic oils, which really don’t like to go into solution, into our beer. Whirlpool hopping uses higher temperatures to force the oils into the beer, while dry hopping uses time (at a lower temperature). The two techniques are better at preserving different hop oils, which is why we most often use both in a modern IPA.
Whirlpool Hopping and its Limitations
Whirlpool hops are typically added in the “whirlpool” after the boil on a professional system, or alternately the hops are steeped on a homebrew scale. Typically this is done at high temperature but well below boiling. Most aromatic hop oils have a lot boil/vaporization point so they boil off easy, but the higher temperature in the whirlpool does increase the solubility of the oils to get them into the wort quickly.
The main problem with whirlpool hops is that they are added before fermentation. During fermentation a large amount of CO2 is produced that bubbles up through the beer. This scrubs a substantial portion of the aromatic oils out. Also biotransformations from the yeast acts to enhance and free some aromatic compounds, while inhibiting others. An commercial example is shown in the diagram above from Scott Janish. While this is an extreme example using a centrifuge and pasteurization for commercial beer production, you can still see that fermentation alone does substantially reduce the levels of many of the key hop oils.
Looking at the charts, the sum of floral fraction appears to have a substantial drop in fermentation. Myrcene, which has the piny character from many Pacific NW hops also appears to be hard hit during fermentation. Linalool, in contrast seems to survive well post fermentation and even survives the centrifuge. The lower three oils (sesquiterpenoids, caryophyllene and alpha-humulone seem to survive fermentation but are hard hit in the centrifuge.
Also of interest is the fact that hop oil survivability varies quite a bit between different recipes. A, B and C are different beers with different formulations, but one would expect that the hop oils might have a similar survivabillity rate based on their initial levels. However this is not the case, so clearly there are additional factors in play.
Given both terpenoids and thiols (the bulk of aromatic oils) exist both in a free and bound form, and only the free terpenoids/thiols give off significant aroma, it is likely that the mix of free and bound oils plays a large role here. Further, different yeasts can exhibit different abilities to free both bound terpenoids and thiols, so even simple things like the choice of yeast can affect how well your hop oils biotransform into hop aroma in the finished beer.
Several pros I’ve talked with say they have tried eliminating just the whirlpool hops from known recipes and testing them with a triangle test and they were able to tell the difference. Eliminating the dry hops but leaving the whirlpool had a similar result but in a different way. So ultimately whirlpool and dry hops preserve different aromas and flavors. Still I found the chart above interesting enough to mention, as I had not previously considered the significant loss of oils during fermentation.
I hope you enjoyed this week’s article on hops. Thanks for joining me on the BeerSmith Home Brewing Blog. If you want to take the guesswork out of brewing, please try my BeerSmith recipe software from BeerSmith.com. Be sure to sign up for my newsletter or my podcast (also on itunes and youtube) for more great tips on homebrewing.
