Flavor in Evolution and Inebriation

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Flavor may have had an driving role in human evolution. In that same cup, just the flavor of beer may be required to make you feel happy, no alcohol required.
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Bar Stools and Molecules: Buttery Nipple Science

[Photo Credit: Vince C Reyes]

[Photo Credit: Vince C Reyes]

You may think a buttery nipple is just a fun shot to buy a friend on his or her birthday, but it’s more complex than that. It’s got layers… specifically two. For those not familiar with the bar classic, the buttery nipple is composed of a layer of Irish cream sitting on top of butterscotch schnapps.

Buttery Nipple Shot Recipe

½ oz. Irish cream
1 oz. Butterscotch schnapps

  1. Pour 1 oz. of Butterscotch schnapps into a chilled shot glass.
  2. Carefully pour ½ oz. of Irish cream onto the back of a downturned spoon so it rolls from the spoon and floats on the surface of the schnapps.
  3. Enjoy!

This and other layered shots like the American flag, the B-52, and the Alien Brain Hemorrhage, take advantage of the slight differences in density among spirits. As density, a substance’s mass per unit volume (Density = mass / volume), dictates the layering in these drinks; the most dense liquid is placed at the bottom followed by progressively less dense liquids. In the case of the buttery nipple, the less dense Irish cream floats on the more dense butterscotch schnapps. If you were to reverse the order with the butterscotch schnapps poured on the Irish cream, the layers would not form. The more dense butterscotch schnapps would sink to the bottom of the glass and result in a mixture of the two spirits.

For the home bartender looking to make new layered drinks, the absolute density of a spirit is not always easy to measure. However, a different quantity, specific gravity, is often available online1. Specific gravity is the ratio of the density of substance to water (specific gravity = density of a substance / density of water). Water has a specific gravity of 1.0. More dense liquids have specific gravities greater than 1.0 and less dense liquids have specific gravities less than 1.0. In the case of the buttery nipple shot, butterscotch schnapps (Dekyper’s ButterShots) has a specific gravity of 1.12 while Irish cream (Bailey’s) has a specific gravity of 1.06.1 The specific gravity is often available online for alcoholic beverages because it is important in the fermentation and distillation process, and different beers, wines, and spirits have characteristic specific gravities.

If the specific gravity of an alcoholic beverage cannot be found, some recommend using proof or alcohol by volume (ABV) to layer drinks. Both are mandated on all alcoholic beverages sold and therefore easy to find. In general, proof is the amount of alcohol in a beverage. Specifically in the US, proof is defined as twice the percentage of the alcohol by volume. The alcohol in any beverage you drink is ethyl alcohol, also called ethanol (C2H6O).

Figure 1: Molecular Formula of Ethanol [Image Credit: Vince C Reyes]

Figure 1: Molecular Formula of Ethanol [Image Credit: Vince C Reyes]

At room temperature (77°F or 25°C), ethanol has an absolute density of 789.00 kg/m3 and a specific gravity of 0.7872. As many alcoholic spirits are primarily a mixture of ethanol and water, which has an absolute density of 999.97 kg/m3 and specific gravity 1.0, greater alcohol content can often correspond to a smaller density. For example in the case of the buttery nipple, Irish cream (Baily’s) is 17% ABV, while Butterscotch schnapps is 14.8% ABV. Therefore, the higher alcohol content and corresponding lower density of the Baily’s Irish cream allows it to sit on top of butterscotch schnapps. This shortcut, however, is not always correct as many spirits have ingredients other than water and ethanol. Many spirits contain cream, sugars, or other flavoring agents, which can change their densities, making alcohol content an imperfect proxy for density. For example, Smirnoff’s flavored vodkas all have 35% ABV, but have varying specific gravities: citrus vodka has a specific gravity of 0.96, while the more dense watermelon vodka has a specific gravity of 0.981.

Figure 2: Layering in a Buttery Nipple.  *ABV is not always an indicator of density. [Image Credit: Vince C Reyes]

Figure 2: Layering in a Buttery Nipple.
*ABV is not always an indicator of density. [Image Credit: Vince C Reyes]

Lastly although other factors such as altitude affect density, temperature is the other most relevant factor for an aspiring bartender. Liquids are denser when cold. Temperature is an indicator of the speed of molecules within a substance. At low temperatures, liquids have slower moving molecules that pack closer together resulting in greater mass per volume. In contrast, at higher temperatures, molecules in liquids move around more quickly and take up less space resulting in a reduced density. For example, water near room temperature (70°F [21°C]) is less dense (0.998 g/cm3), than water near freezing (1.000 g/cm3 at 39.2 °F [4.0 °C])3. This is why using chilled spirits, glass wear, and spoons when making a layered shot can ensure that spirits remain at their densest and form layers.

Ultimately, a great layered shot is one that is not only effectively layered, but also delicious. If you don’t enjoy the buttery nipple, you now have the scientific knowledge to experiment with your own concoctions!

Learn more

  1. Specific Gravity of Different Spirits from GoodCocktails.com
  2. Specific Gravity of Other Liquids from Engineering Tool Box
  3. The Density of Water at Different Temperatures from the US Geological Survey

Vince ReyesAbout the author: Vince C Reyes earned his Ph.D. in Civil Engineering at UCLA. Vince loves to explore the deliciousness of all things edible.

Read more by Vince Reyes


Roger Pigozzi

Roger Pigozzi studied at the Culinary Institute of America and works at UCLA as the corporate chef and assistant director of dining. In addition to feeding hungry Bruins, Pigozzi also developed and incorporated delicious vegan offerings on the menu.

Roger Pigozzi

What hooked you on cooking?
I think it was growing up in a home where my grandparents lived upstairs. My grandmother and mother were both very good cooks, but I really believe my grandmother was a better cook. She made everything from scratch including pasta, soup, baked bread, and always one special loaf for me baked in a coffee can. My mother was a better baker. She baked a chewy hazelnut meringue and whipped cream cake that was unforgettable. When I was still very young my parents owned a tavern known for its home-style cooking. Food was always a very important part of our family, and for as long as my parents could remember, I said I wanted to be a chef.
The coolest example of science in your food?
At Christmas time when we make gingerbread cookies and add the baking soda to the hot corn syrup I still get a kick out of watching it blow up.
The food you find most fascinating?
It’s the tomato; when you cut it open you see mother nature’s natural gelatin which is more stable and tastier than any gelatin we make. We can eat them raw, roasted, or even oven dried, which transforms even a mediocre tomato into an amazing full flavored tomato.
What scientific concept–food related or otherwise–do you find most fascinating?
The essence of food…the process of dehydration and caramelization whether it’s the part of the roast that sticks to the bottom of the pan; a wine reduction; the oven dried tomatoes that I just mentioned; or oven dried ketchup, “ketchup leather”, to be served in warm sandwiches.
Your best example of a food that is better because of science?
Beta-carotene enriched rice.
How do you think science will impact your world of food in the next 5 years?
I think we will see hydroponic gardens attached to restaurants allowing us to serve more locally produced fruits and vegetables.
One kitchen tool you could not live without?
The French/chef’s knife.
Five things most likely to be found in your fridge?
Flourless bread, soy milk, nuts and grains including steel cut oatmeal (it keeps them from going rancid), extra virgin olive oil.
Your all-time favorite ingredient?
Farmers market garlic and shallots.
Favorite cookbook?
The French Laundry by Thomas Keller.
Your standard breakfast?
Steel cut oatmeal eaten cold with frozen organic blueberries, bananas, flaxseed meal, roasted slivered almonds and soy milk followed by a soy latte or espresso. This is my breakfast 95% of the time.

Square Pies & Salmon Farms

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Math can explain why square pies taste better than round pies and environmentalism can explain why land-based salmon farms are more sustainable.
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Big Soda & Food Perspectives

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An advocate for anti-obesity and healthful diets worked at PepsiCo to change the way food companies marketed junk food. Also, our understanding of how what we eat affects our biology may change with an alternative perspective on food as a hormone.
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