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Old 05-14-2012, 03:37 PM   #1
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Default Does yeast eat sugar?

A reply to my last post talked of yeast eating sugar and inferred the more sugar there is, the more active the yeast is. I thought yeast cells need nutrients, the right temperature range, the right degree of oxygenation - and then they grow and divide. As they divide, enzymes are formed or released, and these enzymes break down fermentable sugars. Is this somewhere near the truth. A reply from a practicing professional brewer would be good also.

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Old 05-14-2012, 03:57 PM   #2
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They use the sugar as food and all the other factors are what make up the ideal environment for them. The by products of their life cycle are alcohol and Co2. You could try PMing revvy on this

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Old 05-14-2012, 03:58 PM   #3
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Quote:
Originally Posted by BOBTHEukBREWER
A reply to my last post talked of yeast eating sugar and inferred the more sugar there is, the more active the yeast is. I thought yeast cells need nutrients, the right temperature range, the right degree of oxygenation - and then they grow and divide. As they divide, enzymes are formed or released, and these enzymes break down fermentable sugars. Is this somewhere near the truth. A reply from a practicing professional brewer would be good also.
I think you might be better suited with a biology text book, or the book Yeast.

You have several questions in there.
Yes yeast "eat" sugar, but there are different kinds of sugars. Enzymes do certain things, fungi do certain things aerobic or anaerobic, bacteria do other things. My guess is you are curious at a level which would be best served with a technical text.
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Old 05-14-2012, 04:31 PM   #4
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Nearly all organisms that we commonly recognize, including yeast, metabolize some form of sugar for energy (plants do too- it's just that they also CREATE sugar with photosynthesis)

Nutrients refer to other compounds that the yeast need to build their own bodies with. Your question suggest that you might also believe that human beings could survive off of nothing but vitamin supplements- these are akin to the "nutrients" that are discussed with regards to yeast.

Grains are mashed to convert starch chains into their constituent sugars, and yeast may use further enzymatic action to break the complex sugars into even simpler ones (just as we break down sucrose into glucose) to make them easier to eat. They don't release enzymes for our benefit, we benefit from their alcohol waste.

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Old 05-14-2012, 05:25 PM   #5
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More Biology: Yeast are a type of fungus. Fungi eat by extra-cellular digestion--they release enzymes, these break down the sugars into what the yeast need, then they absorb those compounds. I'm not sure if they need to do this to simple sugars, but they do for polysaccharides. I think. I know they use extra-cellular digestion.

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Old 05-14-2012, 06:29 PM   #6
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"Eating" is not really what the yeast do, but in simple terms that description works.

In general, the simple answer is that the yeast gain energy from the conversion of the sugar into carbon dioxide and alcohol. In simplest terms, yeast eat sugars and poop and pee Co2 and ethanol. Of course, the metabolic behavior of yeast are more complex than that, but that breaks it down into the simplest way to think about it. The sugar is converted to co2 and ethanol by the yeast.

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Old 05-14-2012, 11:13 PM   #7
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Quote:
Originally Posted by Yooper
"Eating" is not really what the yeast do, but in simple terms that description works.

In general, the simple answer is that the yeast gain energy from the conversion of the sugar into carbon dioxide and alcohol. In simplest terms, yeast eat sugars and poop and pee Co2 and ethanol. Of course, the metabolic behavior of yeast are more complex than that, but that breaks it down into the simplest way to think about it. The sugar is converted to co2 and ethanol by the yeast.
Eating, pooping and pee-ing all used in one thread, just made my Monday!

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Old 05-15-2012, 11:43 AM   #8
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thanks, everybody - but you all dodged the issue of effect of amount of sugar on yeast activity, let us consider 4 beers with OG's of 1025, 1035, 1045, 1055 all 3 gal batches all with a sachet of safale04 sprinkled on top at 25 deg C - I think they would all ferment at same rate but as OG goes up take longer to finish.

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Old 05-15-2012, 11:53 AM   #9
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Quote:
Originally Posted by BOBTHEukBREWER View Post
thanks, everybody - but you all dodged the issue of effect of amount of sugar on yeast activity, let us consider 4 beers with OG's of 1025, 1035, 1045, 1055 all 3 gal batches all with a sachet of safale04 sprinkled on top at 25 deg C - I think they would all ferment at same rate but as OG goes up take longer to finish.
No, they wouldn't necessarily take longer to finish at all. The yeast will reproduce first, and then start fermentation (from aerobic to anaerobic activity).

A full sachet of S04 is overpitching for all of those examples, So they probably wouldn't reproduce much, if at all, before starting fermentation. Since there are plenty of yeast cells, they would be finishing at about the same time.

If the proper amount of yeast is pitched, it's not like a 1.075 beer will take twice as long as a 1.037 beer. They take about the same amount of time, actually.
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Old 05-15-2012, 12:00 PM   #10
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Quote:
Originally Posted by BOBTHEukBREWER
thanks, everybody - but you all dodged the issue of effect of amount of sugar on yeast activity, let us consider 4 beers with OG's of 1025, 1035, 1045, 1055 all 3 gal batches all with a sachet of safale04 sprinkled on top at 25 deg C - I think they would all ferment at same rate but as OG goes up take longer to finish.
Just because you walk into a supermarket piled to the rafters with food doesn't mean you will eat it all... Or even ANY of it. As with you, how quickly or violently the yeast metabolize what food they eat is largely dependent on the strain involved and the conditions of it's health, how many cells there are and what type of food is available.

Additionally, as beer ferments, the levels of oxygen are depleted and the alcohol goes up. More alcohol will definitely negatively effect the rate of fermentation.

There is no DIRECT correlation to speed of fermentation and amount of food available
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