Using simple sugars rather than DME in yeast starters

I was wondering if anyone thinks there would be a true disadvantage to growing yeast starter cultures in a non-traditional (at least in the brewing community) manner: specifically, growing yeast like one would typically do 'in the [academic] lab.' - in YPD (yeast extract, peptone, and glucose) shaking, and at 30C (about 86deg F).

I know people suggest that it is advisable to grow your yeast starters using the carbon source they will be utilizing during fermentation, namely sugars extracted from malt.

But has anyone had negative results using glucose?


For example, I recently made a porter after inoculating 4L of YPD with a vial of WLP002 (English Ale Yeast), shook overnight at 30C, and then pelleted the yeast via centrifugation and resuspended in a minimal amount sterile PBS or something similar.
Based on coulter counter density, I calculated that I pitched some ridiculous amount of yeast - something like 1^14 or 1^15 cells (I'd have to check my notes at home).
Vigorous fermentation took off within (literally) 2 hours and was so vigorous that I had to switch to a blow-off tube instead of an airlock by 4h post-yeast addition to the wort.

The fermentation attenuated fine and the beer was great. So why shouldn't I have used YPD instead of malt extract for my starter?

http://www.mrmalty.com/starter_faq.htm says that, "The sugar in the starter needs to be maltose, not simple sugar. Yeast that have been eating a lot of simple sugars stop making the enzyme that enable it to break down maltose, which is the main sugar in wort. The yeast quickly learn to be lazy and the ability to fully attenuate a batch of beer suffers."

but, this did not seem to be the case for me...the yeast quickly (on the scale of hours) changed their metabolomic/enzymatic expression to consume maltose and other complex sugars.


On a similar note, what about lager yeast starters - is growing at 30C in glucose bad?

I guess I am just being kind of greedy: I have access to shakers and autoclaves and centrifuges that allow me to easily make huge starters....but I want to know if the method I am using is *truly* bad….if I should indeed be using DME or similar as my yeast media?

Granted I did not do a side-by-side comparison of YPD vs. DME as a starter medium, but the one time I've tried using YPD (glucose), I didn't have any issues as far as I can tell.

Is the 'requirement' to use malt extract for your starters just anecdotally-based, or is there data to support that yeast starters grown in simple sugars truly make bad beer?

As an aside, I am not a yeast biologist, I just know via grad student peers how they are grown in many labs.

using pure sugar is unhealthy for yeast. yeast need an assortment of sugars and nutrients to grow properly. during the starter process the yeast make enzymes they need to break down the sugars in the wart. if you use only sugar the yeast will only make enzymes for that type of sugar and will have to take time to adapt to the sugar makeup of your wart. this is stressful for the yeast. when making a starter is best to make a concoction that is the same as the wart you intend to brew.

but if you intend to use sugar in your starter add a healthy dose of yeast nutrient.

But during the aerobic respiration that is occurring in the yeast happily growing in said starter, that maltose, or maltotriose, etc... from the malt extract is just going to be metabolized to glucose anyways so it can enter glycolysis and make ATP...so why provide complex sugars *instead* of just glucose, because, in my (albeit limited) experience, the yeast were capable of metabolizing complex sugars w/i 2 hours after being introduced to the wort (and probably much sooner than 2h as at 2h the wort was going crazy)??


I am not trying to start an argument or discredit the established protocol...I am just looking for some more concrete data, I guess...

yeast need nitrogen to grow healthily. malt is full of nitrogen...sugar is not.

ask a mead maker...we have to add free nitrogen in the form of DAP to our musts or we risk a very slow, possibly poorly attenuated fermentation.
honey is just sugar and water after all.

Between the peptone and yeast extract components of the YPD media I described in my first post, there is plenty of nitrogen in the form of amino acids.

I am not trying to belabor the point, but I must mention again that my fermentation took off within 2 hours!!! I'd assume, then, that my yeast were healthy after being grown as I described above...so why is my method counter to the consensus?

I've gone with a 50/50 of DME and Cane sugar and it worked out fine too. I don't see any reason to do it unless you have to, although sugar is a lot cheaper than DME.

gritmaster said:

Based on coulter counter density, I calculated that I pitched some ridiculous amount of yeast - something like 1^14 or 1^15 cells (I'd have to check my notes at home).

Click to expand...

So you only pitched one cell? That is not a ridiculous amount. It is quite an underpitch I would think.

Let's skip back... can I borrow your shakers, autoclaves and centrifuges?

I would think that if the ferment took off vigorously and hit the desired numbers, then keep doing what you are. I'd keep doing it.

iarobertson said:

Let's skip back... can I borrow your shakers, autoclaves and centrifuges?

I would think that if the ferment took off vigorously and hit the desired numbers, then keep doing what you are. I'd keep doing it.

Click to expand...

Can I borrow those when you're done?

The enzymes a yeast produces are induced by the food source in the environment. The limiting factor is not the sugars (malt sugar and dextrose) but the nitrogen source as well as the free fatty acids. (and possibly micro-nutrients like zinc etc)

Yeast nutrient will supply the nitrogen and the FFA and micro-nutrients.

The yeast may not make as much of the enzymes needed to change malt sugars to glucose, but the "machinery" is still there, waiting to be triggered by the available food source.

Yeast is reproducing by budding, so mutations won't affect many cells. If there is a mutation in the genes for those enzymes, that individual yeast cell will not be able to digest malt sugars, but the other normal yeast cells will out-compete it in the brew.

you can also add a tiny amount of olive oil to help out with the fatty acids yeast need, the amount has been discussed on another thread, but its in the range of 1/100th of a ml or so. (I've been dipping 1/2 inch of a tooth pick into olive oil and swirling it through my starters)

t

My plan is to make a pure cane sugar 1 gal 'krausen' with US05 to add to a very high dexterous RIS that has currently settled in at around 1.041. I'm going to make sure I add yeast nutrient to the krausen batch per the philosophy in this thread. Also, limit O2 and temp after initial pitch. My hope is to kick the ferment back into action. If it doesn't I've just added a gallon of liquid and a very simple sugar that I hope will fully attenuate. Net result should be a lower FG (due to volume increase if anything) and little change in ABV - maybe even a little bump.