For professional and amateur brewers, there is something fabled about “the brew day.” With all the weighing, mixing, boiling, and anticipation during the wort-making process, it’s easy to obsess over every detail, from the degree in the mash temperature to each quarter-ounce of hops on the scale. Amid all the chaos, it’s easy to forget the real character of your beer will come several days after brew day, thanks to a very important ingredient called yeast.

Hops tend to get all the attention in beer making these days, but yeast selection will have the biggest impact on the style and flavor profile of your beer. The difference between an American wheat ale and a German weissbier is minimal when it comes to malt and hops; it’s the yeast that gives weissbier its clove and banana characteristics.

Generally, yeast can be understood by where it originates and how it behaves. The two main types of yeast are lager yeast and ale yeast. Lager yeast are bottom-fermenting, sulfur-producing microorganisms that work best in lower temperatures, between 50 and 55 degrees Fahrenheit. Ale yeast are top-fermenting, ester-producing cells that ferment best in the mid-60s and above.

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In a basic breakdown by region, you can think of American ale yeast as “clean,” English yeast as fruity, and Belgian yeast as complex and flavorful. German lager yeast produces sulfur, while German ale yeast aromas are all cloves and bubblegum. The beauty of all these nuances is that you, the brewer, have the power to harness each strain’s special powers and unleash the flavors and aromas you wish to create.

Bright and Bitter: American Ale Yeast

American ale yeast is a classic choice for a beer with lots of hop aroma and flavor. Its profile is described as clean, crisp, and versatile, meaning it won’t contribute competing flavors or aromas. From pale ales to porters, American ale yeast is a workhorse that puts out very few fruity esters, fusel alcohols, or other strong flavors from fermentation. Without much yeast character, hops have plenty of room to shine.

Juicy and Hazy: English Ale Yeast

The haze craze was made possible in part by the move away from subtler American yeast toward fruitier English yeast. When making “juice bombs” at home, most brewers start with London Ale III. This strain produces esters with apple, pear, kiwi, and honey notes. Ester aromas mingle with hop aromas to accentuate the perception of fruit juiciness.

British yeast is very flocculant, meaning yeast cells quickly clump together and fall out of suspension, dropping to the bottom of the fermenter. For this reason, it typically makes brilliantly clear beers. The haze you expect to accompany a juicy IPA comes later, from dry-hopping during fermentation, and/or from other aspects of the beer, such as high-protein adjuncts in the grist.

Big and Boozy: Belgian Yeast

A high-alcohol beer with more to it than booze, like a Belgian dark strong ale, will need a Belgian yeast strain. There is a huge variety when it comes to Belgian yeasts, with strains selected for the specific esters and phenols they produce. For example, saison yeast is selected for black-pepper-like phenols, while pear- and bubblegum-forward Belgian abbey ale yeast produces the familiar fruity flavors in Westmalle. Brewers in Belgium are obsessed with yeast quality, and have isolated and banked their unique strains so the exact yeast used in brands like Chimay, Westmalle, Achouffe, Rochefort, and more are available to homebrewers. If you want to exactly replicate a classic Belgian beer, check if the yeast strain from that brewery is for sale.

When a boozy beer is the goal, prioritize a yeast strain that can survive in a high-alcohol environment. For a 10 percent-er without esters or much noticeable yeast flavor, look to the workhorse American ale yeast. Dry English ale yeast is a great option for brews reaching above 10 percent ABV. It can create subtle ester aromas in comparison to the American strain, and a temperature-controlled fermentation will keep the esters in check.

Fruity and Sessionable: German Ale Yeast

Just as the beers of Belgium can thank yeast for their telltale aromas and flavors, Germany’s weissbiers largely depend on specific yeast strains. There are several choices for brewing a wheat beer in the 4 to 6 percent ABV range. Some produce more clove-like phenol, while others, like this hefeweizen ale yeast, produce almost none. However, all will be labeled as German ale yeast, so choose accordingly.

The unique fruity esters that add depth to a high-ABV beer do the same in sessionable beers. If you’re looking to make a daytime sipper with more interest than an American pale ale or German lager, try a Belgian blonde using the proprietary yeast strain Belgian Ardennes. It can ferment a beer up to 12 percent ABV, yet it works wonders at low gravity. You can use this Belgian yeast in almost any grist to get pleasant pear and honey notes, and a dry finish.

Smooth Lager: Bohemian Lager Yeast

To make rounded, smooth lagers like the Helles found throughout Bavaria, a Bohemian lager yeast is key. You can find the right yeast for the job under several names, but all relate back to Germany in some way, often referencing Munich. Additionally, all will emphasize maltiness in the fermentation description. Yeasts such as Wyeast 2124 accentuate the soft, bready flavors and the mild toasty notes of malt used in lagers.

It’s important to note that while lager yeast are poor flocculators (staying in suspension longer, meaning more time to hone fermentation flavors), it is tough for the yeast to reabsorb unwanted diacetyl and sulfur at cooler fermentation temperatures. Make sure you do a sufficient diacetyl rest at the end of fermentation to get the most out of this strain while avoiding off-flavors.

Crisp Lager: American Lager Yeast

This is the yeast of choice for brewing American lagers, or many brewers’ and beer lovers’ favorite term, “lawnmower beer.” The fermentation character is clean and crisp, but unlike American ale yeast, it thrives in a cooler environment. It creates a dryness that will highlight hops with the right balance. All yeast creates sulfur and diacetyl, but this particular strain produces them in lower levels, making for an uncluttered flavor profile. Look for strains called American lager.

Sour and Funky: A Mixed Bag

Making sour beer at home is not for beginners. There’s more to it than tossing some wild yeast or bacteria into the fermenter. At the most basic level, there are two ways to go: First, start with a base beer fermented with a strain from above, like American Ale or a Belgian, then add something to funk it up: Brettanomyces bruxellensis (farmhouse, “horse blanket” character), Brettanomyces claussenii (intense tropical character, ripe pineapple), Brettanomyces lambicus (used in Belgian sours; cherry funk), lactobacillus (one-note lactic acid sourness), pediococcus (sour with a funky kick) are examples. You can get them from your local homebrew shop or online.

Second, you can use a pre-blended mix of brewers’ yeast, wild yeast, and bacteria like the Roeselare ale blend used to make Flanders red and brown ales. This microbiological cocktail can be pitched like normal yeast after wort chilling. When using Brettanomyces or bacteria, do your research. These fermenting critters can over-attenuate beer by converting more sugar into alcohol, carbon dioxide, and other byproducts than standard brewers’ yeast, which can ultimately result in (dangerous!) bottle bombs.