Lactose and yeast cell count...

[TanMan15]

Does Lactose factor into how much yeast is required to be pitched?

For example, if I have a wort with lactose at an OG of 1.066, should I still factor how much yeast cells are necessary for that OG since Lactose is not fermentable? Will that OG still require more cells than is typical in a standard slap pack without using a starter?

 

[IslandLizard]

For a 5-5.5 gallon batch of 1.066 beer you should always make a starter. You'd need 252 billion cells for that batch (yeastcalc/homebrewdad).

A pack of WYeast contains around 100 billion cells if made yesterday. It's downhill from there. If it is 3 months old, its viability is only 49%, or 49 billion cells left.

That whole pack with 49 billion live cells in a 2 liter starter on a stir plate would yield a total of 332 billion cells. You can save 80 billion (1/4) out for your next starter, and pitch 252 billion (3/4) into your well oxygenated/aerated wort.

 

[TanMan15]

Ya, but what I’m getting at is, since it will have a higher FG because of the lactose, will it still strain the yeast as much as an OG of 1.066 without lactose? Isn’t that lactose going to push up the OG even though it’s not all entirely fermentable? Will it still need the same yeast count as a beer that will end up with a lower FG?

 

[IslandLizard]

Read this thread.

You may reason that they're not being fermented, but they do add to the sugar load the yeast encounters.

Even if the lactose and other unfermentable sugars and dextrins didn't matter, I'd rather err on the slightly higher side to avoid potential underpitching. How much lactose are you adding? It adds 46 points per pound.

Yeast calculations are not that exact anyway, just modeled estimates.

 

[IslandLizard]

Have you made starters before? It's not that hard.

 

[aprichman]

I would say yes since it's the osmotic pressure that is going to stress yeast.

Island Lizard - viability of White Labs yeast is a lot better now that they've moved to their Pure Pitch packaging. I'm not sure about Wyeast but I think a lot of the amateur information regarding yeast viability over time is really inaccurate.

Having performed these actual assays they can be surprisingly inaccurate without good training.

 

[hopjuice_71]

I won't contend that having a healthy pitch of yeast is important. However, keep in mind that pitch rates and growth calculators are ballpark estimates at best. For example, the doubling time of S. cerevisae is in the single digit hours, even under not so great growth conditions. So, it's hard to imagine if one has decent control over other fermentation parameters (e.g. Temperature) that even if one under pitches by 1/2 it will result in a bad batch. this being said, if you pitch at an estimated 10-20% of the recommended number of cells, you may have some issues. Personally, even if your batch was 1.060 without the lactose, I would go with a starter or vitality starter, unless your yeast sample (assuming 100b cells starting) was uber fresh.

Hope this helps.

Cheers!

 

[aprichman]

https://www.whitelabs.com/news/purepitch-shelf-life

 

[hopjuice_71]

Ugh, I was slow. Totally agree with aprichman. Estimates are not necessarily good and are totally strain dependent, which is rarely (never?) accounted for.

 

[IslandLizard]

https://www.whitelabs.com/news/purepitch-shelf-life

That shelf life is indeed impressive! 90% vitality after 3 months.
I guess we can mimic those percentages in our calculators to get better estimates on yeast starters.

Now the OP has one WYeast smack pack, so stick to the old, then?
I do think the calculators have always been very conservative from the start. Yeast technology has progressed tremendously the past 5-10 years, while the calculator models haven't and are now 10 years old.

 

[hopjuice_71]

Well, regarding the OP, if it were me, if I had a super fresh pack, i would just go for it. Anything a little bit old, or stored under less than optimal conditions, I would do a vitality starters or a full-on starter.

A bit off topic, we work with different strains of the same species of microbe in the lab all the time, and they often have quite different growth characteristics (up to 2X different doubling times and/or lag times), even under optimal conditions. Same goes for viability after storage in a fridge or freezer. So, what this suggests to me is that proper viability and growth models really need to be done on a strain-by-strain basis (assuming good handling before the yeast gets into our hands). Annoying, but I take some solace in the anecdotal evidence that pitch rates are quite forgiving, at least when the yeast is fresh and healthy.

Cheers

 

[IslandLizard]

Still, wouldn't the OP need at least double the (100 billion) cells in a typical WLP or WYeast yeast pack for his 1.066 wort?

The calculators tells us 252 billion cells needed, that's 2.5 times the amount the freshest yeast pack contains if at optimum vitality.