Orbs of October

Color theory states that orange radiates warmth and happiness by combining the energy and stimulation of red with the cheerfulness of yellow. This is a fit description for the harbingers of autumn’s harvest, the seasonally evocative winter squash and pumpkins.

Did I mention that the “Great Pumpkins” have arrived in the Regenstein Fruit & Vegetable Garden?

PHOTO: Atlantic Giant pumpkins.
Unbelievable, yet real: Atlantic Giant pumpkins (Cucurbita maxima ‘Atlantic Giant’) adorn beds of parsley, chard, and heirloom root vegetables.

So visually compelling is the color-saturated rind of the world’s largest fruit, and so heavy. All of this certainly explains what your fruit and vegetable team has witnessed in the Garden. There is pure joy as our visitors first glimpse the great pumpkins—ooohs and ahhhhs and squeals of delight, as folks of all ages decide how best to connect with the fruit: Is it real? Should I touch it? Should I sit on it? Hug it? Photograph it? People even talk to our anthropomorphic fruit. 

But the giant pumpkins are just one part of the diverse Cucurbita garden art growing in the Fruit & Vegetable Garden this season. While they seem to be called “squash,” “pumpkin,” and “gourd” interchangeably, there is actually a science to identifying these cultivars, and pretty much everything called “pumpkin” is really a squash—although “pumpkin” is most commonly used to describe those distinctive orange orbs.

Cucurbita maxima are squash with softer rinds and flesh, growing on long vines with large, hairy leaves. Harder-skinned “winter squash” are typically Cucurbita moschata, including butternuts and acorn squash. They also have trailing vines and hairy leaves, but tougher flesh and rinds, and a ridged but still soft stem. Only Cucurbita pepo are considered true pumpkins, with tougher flesh and rinds, leaves that are downright prickly (not just hairy), and a woody five-sided stem.

PHOTO: Warted hubbard squash.
Warted hubbard squash (Cucurbita maxima ‘Chicago’s Warted’) is delicious now, and delicious later.

Cucurbita maxima ‘Chicago’s Warted’ is an heirloom developed by Budlong Gardens of Chicago. It was introduced by Vaughan’s Seed Store of Chicago in 1894. The 13-pound fruit are dusky olive green, and deeply wrinkled and warted with a classic hubbard squash teardrop shape. These gems have a fine-grained, sweet orange flesh. We planted ours way back at the end of May—perfect timing for this 110-day crop. The hubbards are versatile winter squash that can be eaten right after harvest, or stored until the flesh sweetens around the new year.

PHOTO: Australian blue squash.
Australian blue squash (Cucurbita maxima ‘Queensland Blue’ ) can be stored for an incredibly long time.

A member of the avant-garde Australian blue group of squash, Cucurbita maxima ‘Queensland Blue’ is not often seen growing in the field. While they hail from South America, the blue squash varietals grow equally as well in Australia (for which they are named) because of similar temperatures and length of growing season. We found the seed at Seed Saver’s Exchange in Iowa. This is a bottle-green keeper that, if properly harvested and well-cured with a 4-inch “handle,” will store for more than a year—maybe two. It is a fantastic eating-quality squash with smooth, rich, brilliant orange flesh.

PHOTO: Waltham butternut squash.
Waltham butternut squash (Cucurbita moschata ‘Waltham’) looks like a buff-colored peanut.

Cucurbita moschata ‘Waltham’ looks like a blocky, buff-colored peanut. We planted it in the warm soil of mid-June, which squash of this species prefer. Waltham butternut is a uniform producer that must be harvested before the slightest touch of frost.

PHOTO: Growers and staff positioning a mammoth pumpkin on a forklift.
Moving this Atlantic Giant to its current location took a full day of careful handling…and more than one forklift.

Make sure you have a forklift available before you think of growing Cucurbita maxima ‘Atlantic Giant’, which can easily grow in excess of 1,000 pounds. This squash that looks like a pumpkin surprisingly does not need much more room than the average pumpkin patch to grow, but organic compost can help boost its final size.

PHOTO: Winter Luxury pumpkin.
The champion of pie pumpkins: Cucurbita pepo ‘Winter Luxury’

Cucurbita pepo ‘Winter Luxury’ is diminutive in stature but mighty in taste. The fine, rough netting around the shell is a distinguishing feature of this 1896 heirloom. This is the gold-standard pie pumpkin that can be eaten right out of the garden. It won’t store as long as the other species.

PHOTO: Jarrahdale Australian blue pumpkin.
Stunning when sliced: Jarrahdale Australian Blue (Cucurbita maxima ‘Jarrahdale’)

Cucurbita maxima ‘Jarrahdale’—our second unusual Australian blue—is a deeply-grooved, slate-gray squash with dense, sweet, deep orange flesh and a thin skin.

PHOTO: Pink Porcelain Doll pumpkin.
Purchase Porcelain Doll (Cucurbita moschata ‘Porcelain Doll’) seed from Pink Pumpkin Patch Foundation.

Cucurbita moschata ‘Porcelain Doll’ is a pink cheese pumpkin that has become the symbol of breast cancer awareness among pumpkin growers across America. Growing this decorative hybrid will ensure a donation to research is made.

PHOTO: Small Mixed gourds.
Grown for display, these Cucurbita pepo ‘Small Mixed’ gourds are generally better food for squirrels and raccoons.

There are three basic types of gourds in the Cucurbitaceae, or squash family: Cucurbita (ornamental squash), Lagenaria (utilitarian gourds used for things like containers or birdhouses) and Luffa (vegetable sponge). These Cucurbita pepo ‘Small Mixed’ ornamental gourds are just pumpkin varieties with poor flesh quality—either too fibrous or too watery for eating—but with beautiful color and texture for use in fall arrangements. We grew these up on a trellis. They store better in a cool environment but can easily last indoors for seasonal holiday decorating.


Choosing a pumpkin this weekend?
Use these tips and know what you’re selecting when you shop:

PumpkinHandle pumpkins carefully, by using two hands to lift them. Although it is tempting to pick pumpkins up by the “handle,” a pumpkin’s decomposition accelerates once the stem has broken off.

Well-grown pumpkins should be heavy for their size, with telltale ripeness indicators like deep, saturated color, and brown stems. The rind should be hard—impenetrable when lightly pressed by a fingernail—and have a glaucous, dull sheen.

Once you get your pumpkin home, wash the rind with a mild bleach solution to remove bacteria and extend the life of the pumpkin.


I just cannot resist asking: Orange you glad you visited the Regenstein Fruit & Vegetable Garden? Learn more about pumpkins in Plant Information and The Smart Gardener.


©2013 Chicago Botanic Garden and my.chicagobotanic.org

Extreme Pumpkins

Riley Obenchain conjures a feeling of mischief and magic.

He wears a tattered straw hat, trimmed with a red poppy, that looks like something a scarecrow might wear. His bushy black eyebrows dance when he talks, bringing to mind the woolly bear caterpillars abundant in the fall. A playfulness—tinged with the macabre—also shows in the jack-o-lantern characters Obenchain creates each year for HallowFest, the Garden’s popular, family-friendly celebration of Halloween.

PHOTO: Riley Obenchain with giant pumpkins.
Riley Obenchain poses with some enormous jack-o-lantern fodder in the Regenstein Fruit & Vegetable Garden.

Obenchain’s ghoulish, yet somehow gallant, jack-o-lanterns provide a mild dose of horror while eliciting smiles and laughs. There’s the tiny pumpkin gripped in the long, pointy teeth of a massive pumpkin. The little guy has a sort of “Oh, no, Mr. Bill” look on his face. The big, toothy smile on another jack-o-lantern gives a mixed message. Obenchain describes it as an “I’m-happy-to-see-you-because-I’m-going-to-eat you” look.

“I get a lot of, ‘Wow! I could never do that!’” says Obenchain, who’s helped keep the Garden’s trams, lawnmowers, and other machinery running smoothly for 35 years, “but in actuality, anyone can do this.” Here are a few of Obenchain’s tricks and techniques, gleaned in a recent interview.

PHOTO: A white pumpkin with a shocked expression and a rubber snake in its mouth.
The removed pieces of the eyes of this “Ernie” are recycled as ears; leftover mouth pieces are used for hands.

Where do you get your inspiration?

A lot of times, the shape of the pumpkin has the idea. The pumpkin determines what you’re going to carve. How is it going to sit? Is it a “Bert” or an “Ernie”? (A Bert has a more elongated shape, while an Ernie has a round, well, pumpkin head. Obenchain is cultivating a large pumpkin this year that has a sort of crocodile look to it.) 

What are your favorite tools?

I like using old-fashioned steel knives. (The steel is more rigid than stainless steel. Obenchain uses a range of sizes and keeps them sharp. He taps them into very thick pumpkins using an old hickory log that he’s kept for years. Toothpicks, bamboo skewers, or even the occasional nail can be used to patch mistakes. A trowel with a sharpened end makes a good seed scooper.)

What sorts of other materials do you use?

Long, skinny gourds for antennaes. Gourds for ears and eyes. One year I used a forked stick for the tongue of a snakelike pumpkin. (Obenchain shows photos of jack-o-lanterns carved by nephews under his tutelage. One looks a little worse for wear, with crosses for eyes and an arrow through its temples.)

What is the biggest pumpkin you’ve ever carved?

An Atlantic Giant squash (Cucurbita maxima ‘Atlantic Giant’). It topped out at 1,010 pounds. (The record-breaker could cover a small table top. Obenchain needed a hand-pruning saw to carve its foot-thick walls. The big galoot had to be moved with a forklift. Another behemoth was so long that Obenchain had to crawl inside to scoop it out, creating the ultimate Obenchain image—a man-eating pumpkin!)

PHOTO: A devilish pumpkin with lots of pointy teeth.
Carving stalks instead of using toothpicks to inset eyeballs ensures they don’t rot out and stay in place while your jack-o-lantern is on display.

While most of the pumpkins carved for Hallowfest are from outside growers, each year, Obenchain tries to grow a few giants of his own in friendly competition with other Garden staff members. This year, he’s growing another ‘Atlantic Giant’ with seeds saved from the thousand-plus-pound monster—if the raccoons don’t get it first!

Join us for HallowFest on October 26 and 27, from 6 to 9 p.m. on Saturday and 4 to 7 p.m. on Sunday, to see Obenchain’s creations for this season.


©2013 Chicago Botanic Garden and my.chicagobotanic.org

Treasure in the Tropics

Hungry for progress, Nyree Zerega, Ph.D., set off in early June to the forests of Sabah, Malaysia, on the island of Borneo.  She was searching for plants in the genus Artocarpus, whose nearly 70 species include jackfruit—the world’s largest tree-borne fruit structure.

Her mission? To gather detailed information about species within the genus, including those that could provide food in tropical areas where it is needed most.

PHOTO: Dr. Zerega and Dr. Joan Pereira climbing hill in tropical forest.
Dr. Zerega in Sabah with Dr. Joan Pereira, her Malaysian collaborator.

On their research trip this summer, Dr. Zerega, a plant evolutionary biologist at the Chicago Botanic Garden, and her research team crossed a small stream on their way into a tropical forest on the edge of a large oil palm plantation. They searched there for an uncommon species until sunlight faded and the light rain turned to a downpour. On the way back, they found that the stream had grown into a raging river several feet wide and deep. Covered in leeches, they held hands tightly and waded across to safety. On other days, they searched for species with leaves as tall as any one of them, and collected fruit weighing more than 20 pounds apiece.

The dish

It’s all in a day’s work for Zerega. She has long traveled to places like this, where she works closely with local scientists to study underutilized food-bearing plants.

PHOTO: Jeisn Jumian with a huge jackfruit over one shoulder, and a cut jackfruit in his other arm.
Jeisn Jumian, field assistant, carries jackfruit back from the field for dinner.

Currently, she explained, the world relies on roughly 30 species to provide the majority of our food. The top three crops—rice, corn, and wheat—account for approximately 40 percent of all food consumed worldwide. We are merely scratching the surface of the thousands of edible plant species in existence, including at least a dozen in the genus Artocarpus.

It’s possible, even likely, that some underutilized crops have as much potential as the current favorites, but simply have not been as developed. “Underutilized crops have the potential to diversify the world’s food supply and improve food security,” said Zerega. She believes the development of these crops, produced close to where they would be consumed, could also reduce the amount of energy used in growing and exporting large quantities of crops around the world. The more options we have, the better off we are, she maintains.

Stocking the pantry

Now back in the Harris Family Foundation Plant Genetics Laboratory of the Daniel F. and Ada L. Rice Plant Conservation Science Center, Zerega and her lab members are busy extracting plant DNA from leaves collected in Malaysia. Also the director of the Northwestern University and Chicago Botanic Garden Graduate Program in Plant Biology and Conservation, she has plenty of helping hands from her master’s and doctoral students.

“We’ll be studying DNA to understand the evolution of Artocarpus, and patterns of the diversity of cultivated members of the genus, such as jackfruit, breadfruit, and the lesser known cempedak, a species believed to have originated in Malaysia. Understanding and conserving genetic diversity is as critical in crop species as it is in wild species,” she said.

PHOTO: The market in Sabah, Malaysia.
Breadfruit is sold at a market in Sabah, Malaysia.

The work is part of a National Science Foundation grant for which Zerega is assembling a taxonomic revision, which is like a genealogical history. It will include descriptions of all the Artocarpus species, how to identify them, where they originated, where they are found today, how they are used, and how they are related to one another.  

Dried, pressed specimens of all the plant samples used for DNA will be stored in herbaria in Malaysia and the Garden’s Nancy Poole Rich Herbarium. Zerega serves as director of the herbarium. These specimens, along with photographs, serve as documentation of each plant.

Cooking up solutions

PHOTO: A plate of fried breadfruit with dipping sauce.
Fried breadfruit from a market near Kuala Lumpur, Malaysia.

Next, Zerega hopes “to focus on ways to conserve the diversity and increase the use of underutilized species such as jackfruit and breadfruit, because they hold great potential for increasing food security in food-insecure parts of the world, many of them in tropical areas where Artocarpus species grow.”

As she considers her research, Zerega occasionally finds time to stroll her favorite areas of the Garden—the Dixon Prairie and the McDonald Woods.

From working with students and collaborating with scientists around the world, she hopes her work will contribute to the conservation of underutilized crop diversity and food security around the world. Although she has already accomplished a great deal, it seems that Zerega’s work so far is just a taste of what is to come.

Read more about Zerega’s research in Papua New Guinea, the Northern Mariana Islands, Hawaii, and Bangladesh in the Spring 2013 issue of Keep Growing.


©2013 Chicago Botanic Garden and my.chicagobotanic.org

The Evolution of a Research Idea

Five years ago this past May, I found myself starting a new job and a new research project. My job, of course, was as a conservation scientist here at the Chicago Botanic Garden, and the research project had me sitting on the side of a road at dusk in Pueblo West, Colorado. I sat there in front of a group of plants that produce lovely-smelling flowers, waiting for their impressive pollinators to show up. And when they did, I snapped some of my very first photos of these beauties: hawkmoths, better known as the five-spotted hawkmoth, or to the scientific community as Manduca quinquemaculata.

PHOTO: Night photo of hawkmoth sipping nectar from evening primrose.
A five-spotted hawkmoth (Manduca quinquemaculata) drinks nectar from the Colorado Springs evening primrose (Oenothera harringtonii) as the flower begins to open. Pueblo West, Colorado, May 2008. Photo: Krissa Skogen

Just this past Friday, I visited the National Science Foundation’s Dimensions of Biodiversity Program, to find this very same photo—and the research that my colleagues and I will conduct over the next five years—highlighted.

So how did this one photo go from being taken in the spring of 2008 to being highlighted on the NSF’s website? How does a research project evolve and grow over time? Ask any scientist what they are currently working on and their answer will almost always start with, “I was first fascinated by x back in y….” Something caught their attention, sparked a thought, pulled them in—and they continued asking question after question, developing hypotheses and gathering data to test them, with their answers pushing them forward, sometimes down unanticipated paths, and sometimes into much bigger or smaller arenas. The more one knows, seemingly, the less one knows; old questions are answered and new ones are developed. This is what pushes scientists, and science, forward.

The evolution of a research idea

PHOTO: Krissa Skogen poses with primrose in New Mexico.
Krissa Skogen poses with an evening primrose in New Mexico. Photo: Chris Martine

In 2008, I started my current research program. After many conversations with Rob Raguso (Cornell University) and Tass Kelso (Colorado College), I drove out to Colorado with a plan to collect as much information on as many different populations of the Colorado Springs evening primrose (Oenothera harringtonii) as possible in a short period of time. That year, my timing was off—I arrived in Colorado on June 10. Oenothera harringtonii flowers primarily in May. Most of the plants had stopped flowering and so instead of collecting data on floral features, nectar, scent, and pollinators, my field assistant, Evan Hilpman, and I collected data on plant size, health, reproductive success (how many fruits did they produce?) and population size (much like a census). And one striking thing we noticed was this: small white “galls” on some of the green, developing fruits. We took notes on how often we saw this, never anticipating the importance that these little white dots would play in just a few years’ time.

PHOTO: Closeup image of a tiny, white foamy-looking dot (one of many) on a host plant.
We noticed small white “galls” on some of the green, developing fruits. These are parts of the cocoons of tiny little moths, called microlepidopterans, of the genus Mompha. Photo: Krissa Skogen

In subsequent years this project grew, and in the last four years—with the help of conservation scientist Jeremie Fant and other colleagues, and many research assistants and students—we’ve collected data on flower size, nectar volume and sugar content, floral scent, who pollinates and when (hawkmoths come at dusk and visit overnight; bees generally visit in the morning), how populations grow and shrink over time, which other plant species are flowering at the same time, and more. We know a lot of things about this species now, and one thing has been a constant: those little white balls have been observed year-in and year-out in some populations, but not in others.

We know now that some of our populations have an important compound—linalool—and some do not. We know that genetically speaking, our 25 populations function more like three, likely due to the fact that hawkmoths can fly so darn far (some estimates are up to 20 miles in just one night). And more recently, we started gathering more data on those little white balls. It turns out that they are parts of the cocoons that surround the larvae of tiny little moths called microlepidopterans, which belong to the genus Mompha. These moths lay their eggs on flower buds, fruit, and stems. If the larvae eat flower buds and/or seeds, they reduce the number of offspring that the plant produces. This is bad for any plants upon which these moths decide to lay their eggs, but everything must eat, right?

PHOTO: Trio of photos of each life stage of the moth: adult, larva, and cocoon.
Mompha stellella microlepidopteran adult; larva inside fruit (seed predator); cocoon inside O. harringtonii fruit. Photos: Terry Harrison and Krissa Skogen

In speaking with colleagues across the country and in Canada (plant and moth experts, alike), we developed an intriguing story and series of hypotheses we felt were compelling. Do pollinators and floral antagonists both respond to the same attractive scent? Could floral scent be telling hawkmoths and Mompha moths where the flowers are? Pollination is good for plant reproduction, but anything that eats flowers or seeds is not—so how would this trade-off play out in evolutionary time?

These questions have led us to the project that we will pursue on a much larger scale, thanks to recently awarded funding from the National Science Foundation’s Dimensions of Biodiversity Program for our proposal, titled “Landscapes of linalool: scent-mediated diversification of flowers and moths across western North America.”

PHOTO: Bee coated in pollen, inside primrose bloom.
A Lasioglossum species bee robbing pollen from O. harringtonii at dawn. Photo: Sadie Todd

Relationships among flowering plants and insects represent one of the great engines of terrestrial diversity. Floral scent and other plant volatiles are important drivers of these relationships (e.g., pollination, herbivory, plant defense), but remain poorly integrated into floral evolution and pollination ecology. Few studies have tested the spectrum of plant fitness outcomes when scent attracts both pollinators and floral/seed enemies. Thus, the hidden diversity of floral/seed predators and their potential as selective agents constitutes a considerable gap in pollinator-centric understanding of floral evolution. These “forgotten predators” have co-diversified with flowering plants and are likely influential in the evolution of most plant-pollinator interactions.

PHOTO: Five-spotted hawkmoth extending its proboscis (longer than its body) into a primrose bloom as it hovers.
A five-spotted hawkmoth (Manduca quinquemaculata) probes an opening evening primrose flower for nectar with its proboscis. Photo: Krissa Skogen

This project is ambitious and large and pulls upon a wide variety of expertise. In total, there are 11 Ph.D. scientists collaborating on it, including myself, Jeremie Fant, and Norm Wickett here at the Garden. The others include Robert Raguso (Cornell University), Rachel Levin (Amherst College), Terry Harrison (University of Illinois at Urbana-Champaign), Jean-Francois Landry (Agriculture & Agri-Food Canada, Eastern Cereal and Oilseed Research Centre), Sylvia (Tass) Kelso (Colorado College), Kathleen Kay (University of California, Santa Cruz), Mike Moore (Oberlin College), and Warren Wagner (Smithsonian Institution).

We are excited about what we’ll uncover in the next five years and will update you with progress as our discoveries unfold!


©2013 Chicago Botanic Garden and my.chicagobotanic.org

The Science (and Language) of Beer

PHOTO: Carboy full of beer in process of brewing.
The standard equipment for the home brewer: a 6-gallon glass “carboy,” a device that fits right on top of the carboy rim called a universal carboy cap, and an air lock.

Although I’m a scientist by trade, I’ve also joined the ranks of home/craft beer makers, and have done a fair bit of brewing myself.

Despite seemingly endless beer varieties, beer making boils down to just a few basic ingredients. So what’s really happening during the major steps in the brewing process? And what do all those colorful beer-making terms mean?

Step 1: Choosing the grain

The basic brewing process begins with grains—generally barley, but also rice, wheat, and/or sorghum. Botanically speaking, grains are grasses with a special type of seed called a caryopsis. Inside a caryopsis is an embryo and a large, starchy food reserve (called the endosperm) that plays a key role in the beer-making process.

Step 2: Making the malt

As a grain seed germinates, its food reserve is converted from starch into smaller carbohydrates. This conversion process is important for the brewer, since those carbohydrates will feed the yeasts during fermentation. The brewer doesn’t want the grain seed to completely germinate, though—if it did, the embryo would “eat” all of the food reserves, leaving none for the yeast.

Instead, grains are only partially germinated, just enough for their starch-converting enzymes to become active. Then the grains are gently heated and dried, so that the enzymes stay active (it’s called diastic power), but the embryo remains inactive. It’s a process known as malting, and its end-product is the key ingredient in most beers: barley malt.

PHOTO: Hands holding partially germinated barley seeds.
Malted (germinated) barley is used as a base in beer and scotch. Photo via Finlay McWalter, Wikimedia Commons. GFDL

Step 3: Blending the malt

By treating barley malts differently, the brewer can create different colors, flavors, and sweetness levels in their brew. Roasting, for example, affects depth of color and flavor, while using malts with different diastic powers—that ability to convert starch into sugar—affects sweetness. The blending of barleys and barley malts (plus other grains) is part of the art of brewing beer.

Step 4: Mashing the malt

In the process called mashing, malt sugars are extracted from the barley by adding hot water during the starch-converting process. Water dissolves the starches so they leach out of the cracked grain, creating the wort, which is like a syrupy malt tea. Already-prepared malts—and even malt-extract syrups—allow the home brewer to skip the mashing process.

Step 5: Boiling the wort

Home brewers can simply turn up the heat on malt syrup plus hot water to boil the wort—an important step that denatures, or kills, the enzymes that convert starches into sugar. This kills any microorganisms and bacteria in the process, too. Now the art continues, as the brewer can control fermentation and flavor with yeasts and hops.

PHOTO: A blooming hops vine.
A beautiful vine for the home garden is hops (Humulus lupulus), pictured here in flower.
PHOTO: Hops "cones", the pollinated product ready for harvest.
Pollinated and fruited in fall, these pale green hops “cones” supply the resins that give beer its bitter (or bright) flavor.

Step 6: Choosing the hops

Hops add flavor—described from bitter to bright—and can be introduced at the beginning of the boil, midway through, or as finishing hops at boil’s end. Timing plus variety choice (more than 80 varieties of hops are available) determine flavor. Bitter flavor is the result of adding hops at the beginning of the boil, while the characteristic bright, hoppy flavor of India pale ales comes from hops added to the cask after fermentation.

Step 7: Pitching the yeast

Yeast gets added after the wort has cooled sufficiently, in a process called pitching. There are two yeast groups to choose from.

  • Ale yeasts, which work at the top of the fermentation tank, produce ales, porters, stouts, Altbier, Kölsch, and wheat beers. Ale yeasts prefer warm temperatures, going dormant below about 55 degrees Fahrenheit.
  • Lager yeasts, which prefer the bottom of the tank, yield Pilsners, Dortmunders, Märzen, Bocks, and American malt liquors, and work happily at 40 degrees F.

Yeasts contribute to flavor, too, creating secondary metabolites such as the phenolics that give German wheat beers their characteristic clovelike flavor. Brewers can experiment with yeasts: California common beers, such as Anchor Steam Ale, were created by adding lager yeasts at ale temperatures (60-70 degrees F.).

PHOTO: A "flight" of four beers, showing different colors and ales.
Porter, lager, stout, and ale: different malt blends and yeasts create different brews.

Step 8: Fermentation

Fermentation is a preserving process known since Neolithic times: beer, wine, pickles, sauerkraut, and hot pepper sauces are all fermented. Yeasts cause fermentation by converting the sugar in the wort to alcohol. When yeasts—either dry or liquid—are pitched into a well-aerated wort, a controlled population explosion occurs. Yeasts suddenly go into metabolic overtime, reproducing at a rapid rate. Fermentation begins as sugars are consumed. The amount of sugar in the wort, the temperature at fermentation, and the type of yeast pitched determine the metabolic byproducts: alcohol and CO2.

Step 9: Conditioning

Fermentation is a two-stage process. Primary fermentation occurs after the controlled population explosion, and begins to subside, or attenuate, as the alcohol content increases. Alcohol rises to the top of the fermentation tank, while most of the yeasts fall to the bottom and become inactive. (Some do not.) Most brewers transfer the wort to a secondary fermentation tank at this point; the second fermentation occurs more slowly, and conditions the beer as the more complex sugars are converted. Once the beer is fully conditioned, it’s bottled or transferred to a cask or keg.

Think about the science next time you speak the language of beer and order a light, crisp, transparent American lager…a rich, creamy, almost-opaque stout…or something in between.

And which kind of beer most appeals to me? I often have trouble choosing between a bright, crisp India pale ale such as Sierra Nevada, or something a lot darker, like a Guinness. I guess I’m just a fan-atic!


©2013 Chicago Botanic Garden and my.chicagobotanic.org