Saccharomyces pastorianus is understood to be
Answer: C
Genome studies show it to be an interspecies hybrid, which explains its ability to work at temperatures far below those an ale yeast tolerates. The cold-tolerant parent, Saccharomyces eubayanus, was identified long after the yeast had been in use.
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Bottom fermentation is typically carried out at
Answer: D
Lager yeast works effectively at 5 to 10 degrees, producing carbon dioxide slowly so there is little turbulence and the yeast settles early in the process. Ale fermentation runs considerably warmer, typically in the high teens or low twenties.
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A practical consequence of the low temperature used for lager is that fermentation
Answer: A
Cold slows the yeast, so a lager ferments over weeks where an ale may be finished in days, and it is then matured cold for longer still. The slower, cooler fermentation is part of what gives lager its cleaner flavour profile.
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Lagering refers to
Answer: B
The word means storing, and the cold maturation period lets the yeast settle, allows unwanted flavour compounds to be taken up again and gives the beer its clarity. The other operations belong to earlier stages of the process.
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Diacetyl in beer is perceived as
Answer: C
Diacetyl gives a butterscotch or toffee note that is a fault in most styles. Yeast produces its precursor during fermentation and then reabsorbs and reduces it during conditioning, which is why a beer taken off the yeast too early can taste of it.
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A diacetyl rest during brewing involves
Answer: D
Raising the temperature towards the end of fermentation speeds the yeast's own reduction of diacetyl to compounds with much higher flavour thresholds. It is a biological solution: the organism removes what it earlier produced.
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Flocculation of brewing yeast refers to its tendency to
Answer: A
Flocculent strains aggregate and drop out once fermentation slows, which clears the beer and makes the yeast easy to recover. A strain that flocculates too early may leave the beer under-attenuated and sweeter than intended.
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Attenuation in brewing describes
Answer: B
A highly attenuated beer has had most of its fermentable sugar converted, so it finishes drier and stronger, while low attenuation leaves residual sweetness. It is a measure of how far the fermentation has gone rather than of any flavour compound.
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Adjuncts such as maize or rice are used in brewing chiefly to
Answer: C
They are unmalted sources of starch, so they add fermentable extract at lower cost and give a lighter flavour and colour. They bring no enzymes of their own, so enough malt must be present to convert them as well as itself.
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Carbon dioxide in a finished beer may come from
Answer: D
Traditionally the gas of a secondary or conditioning fermentation is retained under pressure, and in modern practice carbon dioxide is often added to a filtered beer instead. Both routes give the same gas from a very different origin.
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