Presentation on theme: "The Science of Brewing Beer"— Presentation transcript:
1 The Science of Brewing Beer Sarah OppeltCurrent member of Tolan Lab, Boston UniversityFormer Microbiologist & QC Manager, Brewery Ommegang
2 The Science of Brewing Beer Overview of Brewing Process & IngredientsWhat contributes to the flavor of beers?FermentationHow Yeast is Really Controlling Everything
3 Hops, or other additives IngredientsWaterMalted GrainsHops, or other additivesYeast
4 The Mineral Content of Water Will Have Subtle Effects on Flavor Ca++ and Mg++ (hardness) will effect yeastmetabolism and growth rateHCO-3 (bicarbonate) will effect thepH of the fermentation
5 Malted Grain Provides the Sugar for Fermentation The more roasted a grain is, the more it contributestoasted and caramel flavors. However, darker roasted malts provide less simple sugars.
6 Hops Contribute Bitterness! Hops are a surficant that also contribute to headformationbecause of their ability to stabilize bubblesby increasing surface tension.Our ability to distinguishlevels of bitterness is very imprecise.
8 3 Types of Yeast Used in Brewing Ale yeasts are top-fermenting,can ferment at higher temperatures,and tend to produce more esters.Lager yeasts are bottom fermenting,ferment at lower temperatures,and produce a more “crisp” taste.examples of ales - guiness, any belgian beer, hoegaarden, chimayexamples of lagers - budweiser, pilsnersexamples of wild yeasts or “spontaneous” fermentations - rodenbach, lambicsWild yeasts produce a lot of unusual compoundsand contribute to a “horse sweat” flavorthat is more acidic and an aquired taste.
9 Fermentation in General C6H12O6glucoseC2H6O + CO2ethanolcarbondioxide
10 Major Molecules that Contribute to Flavor & Mouth-feel Length of carbon chain on alcoholAmount of alcohol in the beerAmount and type of esters producedResidual sulfur compoundsCarbonation
11 Metabolism Involved in Molecules that Contribute to Flavor GlucoseDHAP+ Glyceraldehyde-3PG3PPyruvateEthanol+ longer chain alcoholsAcetyl-CoAEstersFatty AcidsCitric Acid Cycle
12 Factors effecting Fermentation Mineral Content of WaterTemperature of FermentationPitch Rate of YeastAmount of AerationLength of Fermentation
13 The faster a yeast grows and the longer the exponential growth phase is, the more esters will be produced.
14 The faster a yeast grows and the longer the exponential growth phase is, the more esters will be produced.
16 Common Esters & Their Flavors Ethyl acetate is the most common ester, and smells like nail polish remover. However, sensory threshold for this molecule is very high, so it isn’t usually noticed.
17 Common Esters & Their Flavors Isoamyl acetate has a very low threshold for detection. It has a “fake bananas” flavor and is found in a lot of Belgian and wheat style beers.
18 Common Esters & Their Flavors Isoamyl acetate has a very low threshold for detection. It has a “fake bananas” flavor and is found in a lot of Belgian and wheat style beers.
19 Common Esters & Their Flavors Ethyl butyrate has a low to medium threshold. It giveshints of passion fruit or pineapple.
20 Common Esters & Their Flavors Ethyl hexonoate has a low to medium threshold. It lends a red apple or anise like flavor.
21 Budweiser Grains & Hops: Pilsner malt, medium amount of hops Yeast: S. ovarum, (formerly S. carlsberges)Fermentation: 15°C for 2 wks, with longer lagering period. Wood chips are added to help yeast flocculateOther: Filtered beer and force carbonated.
22 Pabst Blue RibbonGrains & Hops: Pilsner malt, medium amount of hops, majority of sugar comes from cornYeast: S. ovarum, (formerly S. carlsberges)Fermentation: 15°C for 2 -3 wksOther: Filtered beer and force carbonated.
23 GuinnessGrains & Hops: dark roasted malts give the color, light roasted malts provide sugar for fermentationYeast: S. cereviseaFermentation: 18°C for 2 -3 wksOther: Filtered beer and force carbonated with nitrogen. The creaminess comes from the feeling of the smaller bubbles.
24 HoegaardenGrains & Hops: lighter roasted malts and wheat, low to medium hopsYeast: S. cereviseaFermentation: 18°C for 2 -3 wksOther: Beer is unfiltered and refermented in the bottle for natural carbonation
25 RodenbachGrains & Hops: lighter roasted malts and wheat, low to medium hopsYeast: “wild” fermentation, spontaneous mixed cultureFermentation: 18°C for 2 -3 wksOther: Beer is filtered and refermented in the bottle for natural carbonation