Yeast Starters

Discussion in 'Homebrewing' started by WHTLBCK74, Oct 3, 2012.

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  1. WHTLBCK74

    WHTLBCK74 Initiate (0) Jan 20, 2009 Pennsylvania

    Hello All. It's been a while since I've posted last. I had made two separate starters two weeks ago. I let one ferment out a stir plate for a few days, put it in the fridge, and then proceeded to do the second one, and did the same with that one. Well, it's been two weeks, and I haven't had time to brew yet. Can I decant, and bump up the starter? Both were 2L starters. What is the life span of refrigerated starters? How does it effect viability? Any foreseeable problems?
  2. ricchezza

    ricchezza Aspirant (249) Nov 2, 2005 Massachusetts

    I would guess that if they've been in the fridge they should be ok. However, and this may be obvious, I wouldn't pitch cold. Allow to warm to room temp. and give another good swirl.
  3. VikeMan

    VikeMan Meyvn (1,484) Jul 12, 2009 Pennsylvania
    Beer Trader

    You will have lost some cells in those couple weeks. If you're concerned, you can use the Mr. Malty calculator or the YeastCalc calculator to estimate what percentage were lost.

    Actually, there are some people who advocate cold pitching. I have done it a few times, and noticed no bad effects. But of course it was not an A/B comparison, so who really knows? My understanding is that yeast thermal shock going from warm to cold is bad, but from cold to warm, not so much. That said, I normally do allow the yeast to warm up to pitching temp (not necessarily room temp), just to be on the safe side.
  4. NiceFly

    NiceFly Aspirant (275) Dec 22, 2011 Tajikistan

    Heat shock from cold to warm is bad, disrupts membrane integrity. This is more relevant to the inital pitch and wide temperature swings.

    Warm to cold does not have any effect on the yeast during pitching, at least that I know of. Dropping the temp during fermentation can slow down the metabolism.

    edit: OP I would not worry too much about a starter that was made on a stirplate in the fridge for a few weeks.
  5. VikeMan

    VikeMan Meyvn (1,484) Jul 12, 2009 Pennsylvania
    Beer Trader

    I haven't heard this before, but if true, I would think it would mean that rehydrating dry yeast (at 95F+) is bad for cell membranes.
  6. NiceFly

    NiceFly Aspirant (275) Dec 22, 2011 Tajikistan

    There is no reason you would have but you can google "heat shock transformation" if you are interested. All the protocols will be for bacteria but the principle is the same.

    There is also plenty of info on Fermentis site about rehydrating yeast and is really out of context here.
  7. hopsandmalt

    hopsandmalt Initiate (0) Dec 14, 2006 Michigan

    This is what I do every time for an average strength 10 gallon batch:
    1. Up to 10 days out I make a 1000 ml starter with 1 vial of white labs yeast fermented on a stir plate until the yeast starts to try to floculate(about two days).
    2. Cold crash overnight.
    3. Decant the spent starter wort off and feed with 1500 ml of fresh wort. Ferment out on a stir plate and cold crash again.
    4. The day before brewing I decant again and feed with 2000 ml of fresh wort and put it back on the stir plate.
    5. By pitch time on brewday the starter is at high krausen and I split it between two carboys.
    I typically get about an 8 hour lag time and very strong, complete, and rapid fermentation with this method. I also use a drop of foam control in the 1500 ml and 2000 ml starters because I only have a 2000 ml flask.
  8. barfdiggs

    barfdiggs Initiate (0) Mar 22, 2011 California

    Heat shock transformation works because of prior exposure/treatment of yeast/bacteria with specific mono or divalent cations (e.g. CsCl, CaCl2) under very non-natural conditions. These conditions don't mimic what you'd see in a yeast starter. Additionally, the mechanism behind heat shock transformation isn't clear, so I don't think this is an applicable explanation for the effects of temperature on starter health/pitching.
    warchez and Soonami like this.
  9. Soonami

    Soonami Initiate (0) Jul 16, 2008 Pennsylvania

    I'll add a couple things:
    • Temperature shock, hot --> cold and cold --> hot is not great for yeast health. When yeast have to deal with extreme temperatures, they adjust their molecular composition to deal with the situation better. This includes expressing heat (cold)-shock proteins and molecular chaperones that helps the essential proteins stay properly folded and function; cell membrane lipids that maintain proper cell wall viscosity and rigidity, etc. Slowly allowing the yeast to adjust to a specific temperature would be best
    • Your starter should ideally be logarithmic growth the when you pitch it into the wort. Usually what this means is that you get a starter going overnight and pitch that into your beer. When the wort runs out of nutrients, the yeast start engaging in stationary phase preparation like making certain molecules to stregthen their cell walls, increasing production of trehalose and glycerol, shutting down metabolic pathways to only the essentials and generally entering dormancy.
    • If you have a large amount of cells from a starter floc'ed out, I'd decant and give it some low OG wort a couple hours before you are ready to pitch into the beer, to warm up the yeast and make sure they are ready to go
  10. MLucky

    MLucky Initiate (0) Jul 31, 2010 California

    Two weeks is probably a little bit long. You're going to lose some cells, but whether or not this would cause problems depends on all the usual variables: your OG, strain, style, and what you're looking for in the finished beer. I would guess that, having made two starters, you are probably OK for most beers under 1.065 or so.
  11. NiceFly

    NiceFly Aspirant (275) Dec 22, 2011 Tajikistan

    There isnt really anything magical about preparing chemically competent cells. A quick search and I found the media, basically it is regular growth media with alot of CaCl2 or MgCl2and some cryoprotectants.

    I suspect the high salt concentration is to effectivley dehydrate the cells making them 1) less prone to lyse upon freezing and 2) more prone to take up the surrounding fluid upon shock. 3) And DNA is negatively charged so that has to be masked so the DNA can get close to the membrane.

    All that is getting a little off topic. While the mechanism for DNA uptake is not clearly defined, heat shocking to disrupt membrane integrity is generally accepted. It is the effect of heat shock on the membrane integrity that makes non ideal for the cells and that premise holds up for heat shocking yeast in wort.

    Speaking of non-natural conditions, how often do you think yeast go from fridge temp to pitching temps in nature?

    edit: Now I sound like HB42, sorry about that;)
  12. WHTLBCK74

    WHTLBCK74 Initiate (0) Jan 20, 2009 Pennsylvania

    Thanks for the responses. I always pitch at temperature, or as close as possible for starters or batch. Now I have a little better understanding why. I will step starters back up & hopefully brew this week.
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