Author Topic: Yeast harvesting and simple sugar  (Read 616 times)

cornershot

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Yeast harvesting and simple sugar
« on: September 23, 2013, 07:58:23 AM »
I was recently advised, when repitching yeast, to not use simple sugars. As I understand it, this is because the yeast will get used to this junk food and become lazy and may not attenuate subsequent batches as well.
Does this apply to top cropping as well? The Belgians use a lot of simple sugars and brew big beers and many (most?) Use top cropping. According to Dave Logston of Wyeast,"the best time to top crop arrives when apparent attenuation slips past 50%,when the yeast head is near it's maximum density, and prior to alcohols increasing beyond 5.25%." (Brew like a monk, page 187)
So is it okay to top crop yeast from beers made with simple sugar?

Online mtnrockhopper

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Re: Yeast harvesting and simple sugar
« Reply #1 on: September 23, 2013, 09:25:41 AM »
I think the intention of the other comment was more like this. If you're brewing specifically to grow yeast for a big beer, and having a drinkable starter is a secondary goal, then removing simple sugars is a good idea. Ideally, a starter would be low OG so as to not stress the yeast. It should also be all malt because malt contains nutrients that yeast need to stay healthy. Simple sugar provides no nutrients and raises the OG. Both of these will stress the yeast and so it does not serve your primary goal.
 
So... I did not answer your question...
 
I think top-cropping is different in a few ways. Yeast is being removed at peak activity and put directly into fresh wort. The yeast have not yet had to attenuate those last bits of sugar in a high alcohol environment which is probably most stressful. Also, top cropped yeast at a brewery is likely to go into similar OG wort, not a higher OG wort, and the higher OG wort makes healthy yeast more important. Maybe the biggest difference may be goals though. A pro brewery wants beer first. Reusable yeast is a secondary goal and there may be some sacrifices being made to produce beer. Many US breweries reuse yeast after fermentation too, and I'm sure many of them use simple sugars.
 
So I guess the answer is that you can use simple sugars when repitching/harvesting/top cropping yeast. It's not the best choice, but it won't ruin your beer either. Seems like most decisions in brewing are not between great / ruined beer - just between better / not as good.
 
I probably made that more complicated than it needed to be.
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Offline reverseapachemaster

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Re: Yeast harvesting and simple sugar
« Reply #2 on: September 23, 2013, 09:34:55 AM »
I'd love to see somebody post something with a remotely scientific basis for this whole simple sugar destroys yeast contention. I'm not saying it's untrue but it seems to be one of those things repeated a lot but never explained how that conclusion was reached.

It's a highly suspect conclusion. During the mash there are lots of simple sugars created, especially if you are mashing in the 140s. It's not like mashes create maltose and more complex sugars. So it really doesn't make sense how a small amount of sucrose or glucose is going to make the yeast lazy. That is especially true since yeast use enzymes to break complex sugars down into simple sugars that they then ferment out. On the other hand, I think you would have a very difficult time making a starter with just water and table sugar because yeast need certain nutrients to grow healthy. However, if you added some table sugar to your starter it would not ruin the yeast.

I would say there is no problem top cropping from a beer with a sugar addition in the boil or afterwards.
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Offline morticaixavier

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Re: Yeast harvesting and simple sugar
« Reply #3 on: September 23, 2013, 10:05:50 AM »
I'd love to see somebody post something with a remotely scientific basis for this whole simple sugar destroys yeast contention. I'm not saying it's untrue but it seems to be one of those things repeated a lot but never explained how that conclusion was reached.

It's a highly suspect conclusion. During the mash there are lots of simple sugars created, especially if you are mashing in the 140s. It's not like mashes create maltose and more complex sugars. So it really doesn't make sense how a small amount of sucrose or glucose is going to make the yeast lazy. That is especially true since yeast use enzymes to break complex sugars down into simple sugars that they then ferment out. On the other hand, I think you would have a very difficult time making a starter with just water and table sugar because yeast need certain nutrients to grow healthy. However, if you added some table sugar to your starter it would not ruin the yeast.

I would say there is no problem top cropping from a beer with a sugar addition in the boil or afterwards.

I tend to agree with your skepticism on this point. I can see how too much simple sugar would dilute the trace nutrients enough to cause a problem but I am pretty sure that many yeast propagators use simple sugars like corn syrup with added trace minerals to grow yeast. This is why Wyeast is gluten free after all. They are NOT using wort to propagate that yeast.
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Re: Yeast harvesting and simple sugar
« Reply #4 on: September 23, 2013, 10:12:03 AM »
I have never heard of such a statement regarding repitching/harvesting yeast. However along those lines when making starters(growing yeast), the sugar needs to be maltose not simple sugar. According to Chris White,"yeast grown exclusively on simple sugar stop making the enzyme that enables them to break down maltose. Since wort is mainly maltose, fermenting it with yeast grown on simple sugar results in a beer that will not attenuate properly."

Offline erockrph

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Re: Yeast harvesting and simple sugar
« Reply #5 on: September 23, 2013, 10:17:52 AM »
I'd love to see somebody post something with a remotely scientific basis for this whole simple sugar destroys yeast contention. I'm not saying it's untrue but it seems to be one of those things repeated a lot but never explained how that conclusion was reached.

Yeah, this seems to be one of those old brewers' myths that seems to keep going, but I've never seen a good test. I have a hard time believing that a starter beer that has 20% simple sugar is going to have any significant effect on the yeast's ability to process maltose. I mean, Belgian beers turn out pretty dry, so those yeast still need to be able to break down malt sugar despite the simple sugar being added. Why would that change on repitching? And even if the yeast does end up producing less enzymes to metabolize malt sugar in response to higher concentrations of simple sugars, why wouldn't those same metabolic pathways produce more enzymes in response to a higher concentration of malt sugar in the repitched beer? I can maybe see an issue with a starter containing 100% simple sugar, but I don't buy this in a beer that has the majority of its fermentables coming from malt.
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