What is Whirlpool Hopping?
Whirlpool or “steeped” hopping is a technique where you add your hops after boiling and let them steep at hot temperature for a period of time before know-out the wort.
Why do Whirlpool Hopping?
The main purpose of whirlpool hopping is not to add bitterness, but instead to capture volatile hop aroma oils in the beer. Most of the aroma oils in hops have a boiling point lower than that of water. As a result the aroma oils will quickly boil off if you add the hops in the boil. So add hops either in the whirlpool or as dry hops to preserve these oils, compare with dry-hopping, whirlpool hopping have higher efficiency.
Whirlpool Hop Utilization
While whirlpool hops are primarily used for capturing aroma oils, the hops are added at a temperature where “isomerization” still occurs. Isomerization of the alpha hops creates “isomerized alpha acids” which are the main bittering compound in beer. So adding whirlpool hops will still add some bitterness to the beer.
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A secondary, and often ignored factor is the effect of boil hops that carry into the whirlpool. For example, imagine adding hops 10 minutes before the end of the boil. That hops will generate some bitterness in the boil, but it will still have quite a bit of alpha acid left as we switch into the whirlpool. So it will continue to generate some bitterness in the whirlpool.
For simplicity, lets first consider the utilization of hops added in the whirlpool, then we’ll look at the more complex boil carryover case.
Calculating hop bitterness in the whirlpool is similar to calculating it in the boil. Hop bitterness is a function of boil (or steep) time, amount of hops used, boil volume, boil gravity, and the alpha acid percentage of the hops. The same basic relationships apply to the whirlpool.
The only major difference is that in the whirlpool, the hops are at a lower temperature, so the isomerization process takes place at a much slower pace. In fact, below boiling it drops off very rapidly. As a result the temperature and time of your whirlpool additions are very important.
If we calculate the hop utilization for an equivalent boil hop using the time, volume and gravity of the wort for the addition, we can then apply the “whirlpool utilization” to this number to estimate the overall hop utilization. Here’s a look at the whirlpool utilization with temperature assuming 100% would be an equivalent boil hop:
- Formula: Utilization = 2.39 * 10^11 * e^(-9773/T) where T is in Kelvin
- Boiling: 100 C (212 F) – Utilization is 100%
- At 90 C (194 F) – Utilization is 49%
- At 80 C (176 F) – Utilization is 23%
- At 70 C (158 F) – Utilization is 10%
- At 60 C (140 F) – Utilization is 4.3%
- At 50 C (122 F) – Utilization is 1.75%
So we can see that the utilization drops very rapidly with temperature. Even at the quite hot 90C (194 F) case we are getting half of the isomerization of an equivalent length boil.
Keep in mind, however, that isomerization is a byproduct of whirlpooling. The main goal of whirlpool hop additions is to preserve volatile hop oils that don’t really want to go into solution and boil off quickly. So often a slightly lower whirlpool temperature can work to your advantage.
The main reason we calculate whirlpool hop utilization is so we don’t accidentally upset the IBU balance of our beer when using a large amount of whirlpool hops.
For hops carried forward from the boil, the utilization calculation is more complex. You first have to have some idea of what percentage of the hop alpha acids were isomerized in the boil, and the amount left that could be isomerized in the whirlpool. From that basis you can then apply the utilization formulas and factors in the whirlpool over the entire whirlpool period.
To do this accurately you need to estimate it for each hop addition individually and then add the result together. The above outline along with the standard hop formulas can get you there.
Whirlpool Hopping Temperature
Whirlpool hopping can be done at different temperature points. The first effective range is what I call the high isomerization range, which is roughly 185–210°F (85–99°C). In this range, the temperature is high enough that some hops alpha acids are still being isomerized, adding bitterness.
This is the range you might use if you still want to add some IBUs to your beer while also adding some hops oils. At the higher temperature, however, you do risk vaporizing a larger portion of hops oils.
The medium whirlpool range is roughly 160–170°F (71–76°C). In this range, there is little isomerization going on, so you will not be adding much bitterness. Also, volatilization is reduced, so you will preserve more hops oils. Fortunately, the wort is still hot enough to allow good solubility for the oils. This is a good compromise range to use if you are looking to preserve hops oils with minimal whirlpool time.
Below that you have the low whirlpool range, which is 150–160°F (60–66°C). In this range, you will volatilize the fewest hops oils, but your hops will also require a longer whirlpool time due to lower solubility at the lower temperature. This is a range you might want to try when trying to preserve oils such as myrcene, which has low solubility and is also highly volatile, as it is less likely to vaporize. This is also a range where many pro brewers have the advantage due to the longer whirlpool times and ability to more accurately control their whirlpool temperature.
SKE brewhouse could carry out the whirlpool hopping process by chill the wort temperature either by wort heat plate exchanger or add dimple jacket on whirlpool tank or with an dedicated tube heat exchanger etc. Talk with SKE project manager team to learn more about whirlpool hopping and how SKE could realize it.