Flavor Esters: An Introduction

Figure 1. Active flavor esters (adapted from Verstrepren et al., 2003)

Many of the fruity flavors (aromas) we perceive in a beer are in fact the products of yeast metabolism and not from the addition of fruits (Figure 1). Some of the esters produced by yeast are considered “off” or undesirable flavors, while others are appropriate at low levels. Some esters even give certain beers (e.g. hefeweizens) their characteristic taste.

To be perceived, the concentration of each ester must meet a specific threshold level; therefore, low levels of ester production will not impart any noticeable aroma. However, esters can have a synergistic effect on individual flavors, affecting overall beer flavor at concentrations well below their threshold⁽¹⁾.

Esters found in beer are synthesized from Acyl-CoA (a long chain fatty acid with Coenzyme A attached, which breaks down into Acetyl-CoA), and fusel alcohols by ester synthase enzymes (e.g. Alcohol acetyl transferase) found in yeast (Figure 2)⁽¹⁾. Beer is not the only place you will find esters; they can also be found naturally occurring in fruits and artificially in many of the candies we eat. In fact, the industry of flavor ester production is in high demand, producing esters for all of those artificially flavored foods and drinks we love to consume in addition to the cosmetics and pharmaceutical industries⁽²⁾.

Figure 2. Enzymatic ester synthesis (Verstrepren et al., 2003)

Unlike ester synthesis in beer, the majority of flavor esters for these industries are produced in labs by chemically synthesizing each compound (Figure 3)⁽²⁾. Recently, the growing trend for “natural foods” has generated a push against the consumption and use of products containing artificial ingredients. These industries have responded by turning to the noble yeast, albeit a different genus and species from those used for brewing, to enzymatically synthesize esters. Esters produced by this process can be labeled as “natural” quelling the fears of the chemically conscientious consumers⁽¹⁾.

Figure 3. Chemical ester synthesis

But I digress...Back to the important things in life, brewing! Temperature, specific-gravity, oxygen, fusel (German for “hooch”) alcohols, and fatty acids all have effects on the production of esters but they may vary depending on the yeast strain. There is a direct relationship between temperature, specific gravity, fusel alcohols, and activated fatty acids (Acyl-CoA, and Acetyl-CoA) with the production of esters⁽¹⁾. The manipulation of these factors is important when considering the style of beer you plan to brew. In general, ales contain higher levels of esters than lagers in part because of the yeast species used (read more) as well as the higher temperatures used during ale fermentation ( above 58°F) compared to those used to "lager" (32°F-56°F). In the next esters post I will talk about each about each factor in greater depth and the mechanism by which they modulate ester production. Until then, happy brewing!

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1. Verstrepren, K.J., Derdelinckx, G., Dufour, J.P., Winderickx, J., Thevelein, J.M., Pretorius, I.S., Delvaux, F.R. 2003. Review: Flavor-Active Esters: Adding Fruitiness to Beer. J Bioscience and Bioengineering 96(2): 110-118 
2. Larios, A., Garcia, H.A., Oliart, R.M., Valerio-Alfaro, G. 2004. Synthesis of Flavor and Fragrance esters using Candida antartica lipase. Appl Microbiol Biotechnol 65:373-376

Beer and Travel: Survival tips for the beer enthusiast

When traveling to a new city, region, or country one of the best ways to explore their culture is through beer. Here are some tips and tricks to maximize your beer traveling experience.

1. Plan ahead

Plan ahead before you travel to someplace new. The Internet is a great resource to look for recommended breweries, bottle shops, and liquor stores. Planning in advance can save you some time and headaches of running into closed or limited business hours.

2. Use your Apps

Phone apps (and corresponding websites) like Ratebeer, Untappd, and Yelp can help you decide on bars, breweries, and bottle shops to visit. They generally provide customer reviews, the number of beers served, and the ambiance of your potential beer refuge.

       

3. Use Public Transportation

Hopefully the city you plan on visiting has some form of public transportation which will allow you to safely (and legally) get from bar to bar. Public transportation can also allow you to stay in cheaper accommodations which can give you a little extra cash to spend on, you guessed it, beer. If there are no public options you can usually get a taxi, rickshaw, or hoof it (as long as it isn’t a DMZ).

4. Find What Locals Drink

Locals generally (I’m looking at you Hákarl and Balut fans) know where the best spots to eat and drink are, follow the crowds. If you find a place not on your itinerary but it is packed out, it may be worth a visit, but great places can also be desolate (la Kiva comes to mind). I usually try to seek out the local brewery tap rooms/restaurants as they generally serve local fare and favorites.

5. Buy in Season (or don’t for some added savings)

Many breweries have special beers that are only available during certain seasons (e.g. Märzens at Oktoberfest) with some beers only being produced in certain regions. By drinking seasonally you can try beers that often only locals get to sample. You can also find some deals on beers that are going out of season. Brewers will often discount beers near the end of their season to make room for the next season’s beer. Watch out not to get last year’s beer.

6. Save some money and Shop at a Bottleshop or Liquor Store

One of the best (and cheapest) ways to sample a regions beer is to visit a bottle shop, liquor store, or grocery store (if they sell beer). They often have large selections of local beer that you would be hard pressed to find in a single bar. Shopping at a bottle shop/liquor store can free you up to sample beers in your hotel room. That’s especially useful for drinking after bars close or those early Sunday mornings when you’re craving a liquid breakfast. The biggest advantage to buying bottles in a shop is cost. Most beers may be half to a quarter of the cost at a bar.

7. Be Prepared and Resourceful

If you plan to buy bottled beer one thing you are going to need is a bottle opener (obviously). There are many options available including shoes with church keys in the sole, bottle openers that fit in your wallet, or on your key chain. There are also the old party trick favorites of using a lighter, a wedding ring, or edge of a table but you want to avoid the ire of your partner or the hotel staff.

                           

Another key to buying bottled beer (if you don’t buy it cold) is cooling it to drinking temperatures. In winter (non-tropical climates) this can be as simple as putting your beer out on a ledge or next to an open window. If your hotel has ice you can always chill your bottle in a trash can full of ice.

                       

If its summer you have a couple of options. You can use the trash can with ice trick or some evaporative cooling tricks. Grab a wash cloth and soak in cold water, then wrap it around the bottle and place on the air conditioning unit or vent. If you don’t have A/C let’s hope you at least have a fan. Point the fan at the bottle with the wet cloth around it and keep it moist to maximize cooling. The fan may only cool it a few degrees but if all else fails go to a bar.

By following these tips you should be able to maximize your beer traveling experience and enjoy new cultures through the unifying power of beer.