|
|
The Beer Science Page |
by George Eldridge 17-Mar-96
John Levin and I, fellow brewers and scientists, set out to determine how to make the ultimate Half and Half. I am not an expert on the history of the Half and Half, but I do know that the authentic Half and Half is made with Harp's Lager and Guinness Stout. Since it was St. Patrick's day, I thought it fitting to experiment with Irish beer.
In a Half and Half the Harp's Lager is placed in the bottom of the glass and the Guinness Stout is placed on top of the lager. The stout and the lager can be made to remain in separate layers. The trick is getting the beers into the glass without mixing them.
The first part of the experiment was to measure the specific gravity of Harp's Lager and Guinness Stout to determine if the configuration with stout floating on the lager is stable. Our results were:
Beer Specific Gravity @ 60F -------------------- ---------------------- Harp Lager 1.011-1.012 Guinness Extra Stout 1.009-1.010 Guinness Pub Draft 1.008-1.009
My initial thought was that the stout would be a higher gravity. My intuition was that the darker beer is a heavier beer. From the data it is clear that my intuition was incorrect.
The difference in the gravities of the beers would allow them to remain separated. These results confirmed that the Half and Half can exist as a stable concoction.
However, the difference in gravity is small enough that temperature differences could have a significant effect. As the temperature increases, the density decreases. Therefore, the stout must remain at a temperature equal to or greater than that of the lager. Even so, the difference is small enough that mixing would readily occur if there were any agitation.
The goal then is to introduce the two beers into a glass with minimal agitation. It was clear that simply pouring the stout on top of the lager would cause too much mixing. We verified this experimentally.
The first attempt to prevent mixing involved the use of a SaranWrap (tm) barrier to keep the beers separated during pouring.The Harp's was poured into the glass and Saran Wrap placed on the top of the Harp's. The Guinness was poured onto the Saran Wrap. The Saran Wrap barrier was then carefully removed. There was very little mixing. This worked very well, but would probably not be suitable for operation on a commercial scale.
The next experiment used a spoon to reduce mixing. The glass was filled with a quantity of Harp's and then a spoon (actually a gravy ladle) was placed level with the surface of the Harp's and the same quantity of Guinness was poured into the spoon. The Guinness was momentarily warmed in a microwave to insure the temperature was greater than the Harp's. There was some mixing due to the agitation caused by the pouring of the stout. The result was a glass with roughly one third pale beer on the bottom and two thirds dark beer on the top.
It was hypothesized that the amount of mixing when pouring into a spoon was a function of the difference in gravities of the beers.We tested this by pouring Guinness, with a spoon, on top of some of my strong ale with a specific gravity of 1.020. There was very little mixing. This confirmed that the amount of mixing is dependent on the difference in specific gravities. Unfortunately, this was not an authentic Half & Half.
We then approached it from the opposite direction. Instead of pouring the stout on top of the lager, we tried pouring the lager under the stout. We did this with a funnel and a short piece of tubing. The stout was poured into the glass and then the tube was inserted to the bottom of the glass and the lager poured into the funnel. The results were not good: there was almost complete mixing. The agitation caused by the lager flowing through the tube was too great. The experiment was a failure, but we drank it anyway.
Then we tried something completely different. Two words: stout cubes. We froze Guinness in an ice cube tray and then dropped the cubes into a glass of Harp's. The thought was that the stout cubes would melt with very little agitation and produce the ideal Half & Half. Unfortunately, the stout from the melting cubes is at or below 32 degrees F whereas the lager is at 45 degrees F. The temperature difference is great enough that the density of the stout is greater than that of the lager. The Guinness forms streamers that pass down through the Harp's to the bottom of the glass. It was interesting, but not the ideal Half & Half.
We then concentrated on the technique of using a spoon. I have heard that the technique in a pub is to use the back of a spoon to deflect the flow of Guinness from the tap into the glass of Harp's. I have also heard that a good server can pull a Half & Half, using the back of a spoon, with one hand. Not having Guinness on tap we were not able to try this.
We realized that some mixing was inevitable when pouring the stout using a spoon. We adjusted the ratio of the lager and stout so that the result was half dark and half light. The ratio was two thirds Harp's and one third Guinness.
The final experiment involved Guinness Pub Draft in the can with the special insert. Twelve ounces of Harp's was poured into a glass and then half a can of freshly opened Guinness Pub Draft was poured into glass on top of a spoon. This produced a beautiful four layer Half & Half. The bottom half was Harp's, the dark Guinness floated on top. The Guinness separated into a dark band and a milky chocolate band of microfine bubbles mixed with stout. The fourth layer on top was the foam.
Bill Nye would have been proud.
Back to my Home Page