Fermentation in brewing transforms sugar into alcohol through the action of a vast colony of one-celled, immotile microbes. Top fermenting and bottom fermenting yeast have different types of action and are used in traditional and artisan brews.
Yeast have been a central part of brewing for thousands of years. These microscopic fungi convert sugars into alcohol and carbon dioxide through fermentation, important to flavor, aroma, and overall character of beer.
Strains in brewing are categorized into two main types: top-fermenting yeast and bottom-fermenting yeast. Originally, top and bottom fermenting yeast refer to the way the yeast is harvested. It's either skimmed from the top of the brew or filtered from the sediment at bottom.
During fermentation, yeast is active throughout the brew, and both bottom and top fermenters create krausen. Over the centuries the strains of yeast have developed their own styles and stories.
Top fermenting and bottom fermenting yeast have similarities, such as
Both convert fermentable sugars into alcohol and carbon dioxide.
Both can be highly strain-specific, meaning different strains within the same species can produce dramatically different flavors and aromas.
Both can be reused in brewing.
Top-Fermenting Yeast
Top fermenting yeast, often called “ale yeast,” ferments at warmer temperatures of 15 - 24°C (60 - 75°F). Flavors are fruity and robust.
Species Used:
The most common species of top-fermenting yeast is Saccharomyces cerevisiae. This species is well-known for its use in creating ales, wheat beers, stouts, porters, and other styles of beer with complex, fruity, and slightly spicy flavor profiles.
Beer Styles include:
Pale ales
IPAs (India Pale Ales)
Stouts
Belgian-style ales
Hefeweizens (wheat beers)
Bottom-Fermenting Yeast
Bottom fermenting yeast becomes popular c. 15th century in Europe. Cooler climates of northern countries like Germany foster development of lagers. The first documented lager, Einbecker, dates back to the 14th century.
Bottom fermenting or lager yeast ferments at cooler temperatures ranging from 7-13°C (45-55°F). This results in a cleaner, crisper flavor profile. Lagers have lower ester and phenol levels due to their cooler fermentation temperatures.
Species Used
The most common species is Saccharomyces pastorianus (formerly known as Saccharomyces carlsbergensis). This hybrid species is typically used in lager production and is thought to have originated from a cross between S. cerevisiae and another yeast species called Saccharomyces eubayanus.
Beer Styles include:
Pilsners: bright, golden lager with crisp and clean taste, often attributed to Saaz hops.
Märzens (Oktoberfest beers)
Helles (Light)
Dunkel: A dark lager with rich caramel and toffee flavors.
Bocks
Tips for Using Yeast in Brewing
Temperature Control: Maintain temperature range for the yeast strain. Warm temperatures of 18-21°C (65-70°F) are better for S. cerevisiae, while S. pastorianus likes cooler conditions at 7-13°C (45-55°F).
Healthy Yeast Starter: Pitch a sufficient number of healthy yeast cells into wort for successful fermentation. Adjust the amount of yeast based on the wort’s gravity. For higher gravity brews, use a larger pitching rate. For example, stronger ales may need 1.5 to 2 times the amount of yeast compared to standard-strength beers.
Clean Equipment: Keep all fermentation equipment sanitized and sterilized to avoid contamination and ensure the yeast remains healthy. Copper vats are often used because copper has antimicrobial properties.
Know the Yeast Strain: Research and choose yeast strains to suit the flavor profile and beer style desired, and have fun with experiments. Belgian ale yeasts often impart spicy and fruity notes, whereas lager yeasts produce crisp and neutral flavors.
Fermentation Time: Be aware of fermentation durations. Top fermenting yeasts often complete fermentation in one to three weeks, whereas bottom fermenting yeasts may require four to six weeks to develop full flavors.
Hydration for Dry Yeast: If using dry yeast, hydrate it according to the manufacturer’s instructions to ensure optimal performance during fermentation.
Oxygen Exposure: Yeasts do best in anaerobic conditions. The frothy krausen they create helps seal off the brew while they're working. It's a mix of carbon dioxide, yeast bodies, secretions and organic matter. Minimize oxygen contact after fermentation starts, especially with bottom fermenting yeasts, to prevent off-flavors and maintain quality.
Non-Fiction Books:
Fiction Books:
READ: Lora Ley Adventures - Germanic Mythology Fiction Series
READ: Reiker For Hire - Victorian Detective Murder Mysteries