Consensus on propagating mother cultures from DVI packets?

[Scarlet Runner]

I’m starting to think about starter cultures: frozen powder DVI vs. mother cultures.  The reason is merely to save a few bucks by making a few more cheeses per DVI packet.  I’ve read several forum posts and it sounds like generally, one can use homemade mother cultures from yogurt (thermo) and buttermilk (meso) with success- however, with varying degrees of reproducibility, flavor and uniqueness in the final cheese.  It makes sense that specific bacterial strains (i.e. frozen powder, direct set stuff) might contribute more to distinct flavors in a cheese, and I don’t want them all to taste the same. For that reason, I’d like to stay with specific bacterial compositions for now, either in direct set starter packets (DVI)- or, in homemade mother cultures of these, if possible.

I poked around and read several different threads on the topic of propagating a mother culture from store-bought, frozen DVI powder.  My understanding so far is based primarily on two threads (http://cheeseforum.org/forum/index.php/topic,2573 and
http://cheeseforum.org/forum/index.php/topic,2110, recommended by Linuxboy) and is this:

1. Yes, you can generate a mother culture from store bought, powdered direct set DVI packets. 
2. To do that, be as sterile as possible, and basically, sterilize some skim milk, inoculate it using your frozen DVI powder, and let it set up. 
3. Yes, you can freeze smaller aliquots of that mother culture in ice cube trays and it will last for 1-6 mo, depending on freezing conditions and sterile technique. 
4. It sounds like the final composition of the mother culture will vary some from the initial powder, in terms of percentage composition and types of bacteria- but that generally it will be a close enough match to get you a similar type of cheese.  Good enough for a home-cheesemaker who isn’t super picky about reproducibility?
5. When using the mother culture, use between 1 and 4 cubes per gallon of milk (following the 1.5 – 2% rule). 
6. If I understand correctly, it sounds like one should only propagate future cultures from a DVI packet for a few generations, before starting another fresh mother culture from a new DVI packet. Right? I think I would probably just culture each packet once (not propagate new cultures from a cube).
7. More generally, when ripening milk (before adding rennet), the point is either (a) to rehydrate and activate frozen, powdered DVI (~30min) or (b) to defrost a frozen cube of mother culture, which when defrosted is ready to go and doesn’t require any real ripening time- one could go ahead and add rennet 5 minutes after adding the cube(s)??  This is where I get a little hazy--- is this right?  I was surprised to learn this- I thought I was allowing bacteria to eat and multiply…

Does that sound about right, or am I mistaken on any counts?
Is there any special procedure for using frozen cubes of culture, or just chuck it into the 90 deg milk and proceed?

Phew!  My brain is going to explode...   Thanks for any direction here!

[Sailor Con Queso]

First - here is my "Making Mother Cultures - A Photo Essay" thread.

I always start a new culture from a TINY bit of DVI to keep bacteria proportions as true as possible to the original. This also avoids contamination and mutations.

Yes, you can freeze in cubes, but try to use fresh unfrozen if possible. It will last for a couple of weeks in the refrigerator, so just pour out what you need and put it back in the fridge. Frozen has to thaw and the bacteria have to wake up before they can start creating Lactic Acid. Of course while your milk is heating up, you can place a cube or two in a small glass of warmed milk to thaw out quicker. Fresh is awake and active instantly.

Technically, you are looking for a pH of around 6.5 but in general, without a pH meter you can wait just 15 minutes and then rennet, so fresh saves a lot of time (and money).

[linuxboy]

It sounds like the final composition of the mother culture will vary some from the initial powder, in terms of percentage composition and types of bacteria- but that generally it will be a close enough match to get you a similar type of cheese.  Good enough for a home-cheesemaker who isn’t super picky about reproducibility?

Generally, this is true. You can achieve repeatability if you re-culture from the DVI each time, like Sailor posted in his thread.

If I understand correctly, it sounds like one should only propagate future cultures from a DVI packet for a few generations, before starting another fresh mother culture from a new DVI packet. Right? I think I would probably just culture each packet once (not propagate new cultures from a cube).

The reason I advocate using DVI each time for each fresh batch is because it is more consistent for people who do not have training in microbiological methods. If you know what you're doing, you can propagate however you want.

More generally, when ripening milk (before adding rennet), the point is either (a) to rehydrate and activate frozen, powdered DVI (~30min) or (b) to defrost a frozen cube of mother culture, which when defrosted is ready to go and doesn’t require any real ripening time- one could go ahead and add rennet 5 minutes after adding the cube(s)??  This is where I get a little hazy--- is this right?  I was surprised to learn this- I thought I was allowing bacteria to eat and multiply…

No, not a with cube. Cube would take 15-20 mins, and you would need to make assumptions about viability. Yes, with fresh mother culture, 5 mins is enough. I will literally temper the mother to make sure it's dissolved, then dump it in the milk, mix, and then get the rennet, measure it out with a syringe for small batches, mix it up, and add right to the milk right away. All the in-between walking, measuring etc takes 4-5 minutes.

[Scarlet Runner]

 Sailor,
Thanks for posting the link to your photo essay; I had not seen this yet, and is very helpful.  It sounds like the reasoning behind making mother/primer cultures is a little more complex than I had thought about... For me initially, it was a way to think about stretching my cheese-making dollars just a bit more- but I still had in mind to freeze cubes of it, for the convenience to pull out whenever I make another small (1 or 2 gallon) batch of cheese (maybe 1 or 2 cheeses per month??).  And your reply makes this option even more frugal, since you use only very small amounts of DVI to inoculate. 

What I am now beginning to understand is the benefits of standardization of the process (analogous to flocculation, like you say) by using fresh bacterial cultures... which means using the fresh culture is part of the whole point. I didn't get that before; I'll have to think about how to adapt this to my very small scale situation (I can't make or eat enough cheese to use this all fresh).  But- since I'm not as worried about time as larger scale professional producers, maybe taking the time to ripen using a few frozen cubes is not as big a deal for me...

For letting a Meso primer culture set at "room temp", will 60F do the job?  My house is cooler than most.

I like your idea to just sterilize the whole darn quart of milk; much easier than Mason jars...

From your discussion with linuxboy I can see that using fresh primer/mother cultures leads to some significant benefits, that you forfeit when using DVI powder.  Is the latter true for frozen aliquots of those primer/mother cultures- that you lose those benefits because you are stopping bacteria at their prime, whether it's by drying or freezing? (e.g. Would frozen cubes of primer still yield "Better accuracy with bacterial population targets; Better acidity at rennet makes for a better curd set. I am getting much stronger curds.")?  Obviously, the benefit of saving time is lost...

linuxboy,
Thanks for your corrections about using the cubes and correcting for viability; makes sense.

[linuxboy]

For letting a Meso primer culture set at "room temp", will 60F do the job?  My house is cooler than most.

No, you must keep a constant temp at the optimum level for the bacteria type. Most cultures you have are mixed defined or undefined species with temps that vary based on the strain. Meaning you could not culture something like flora danica at the same temp as you do a cheddar culture.

Would frozen cubes of primer still yield "Better accuracy with bacterial population targets;

frozen is in between DVI and fresh. Longer lag, but not as long as DVI

[Sailor Con Queso]

By golly I think you've got it.

Room temp of 60 will work, but it will take longer. But as LB says, there are optimal temps that will maintain the species proportions better. Same thing with the amount of DVI that you add. Tiny amounts just take longer to set. Without a pH meter, just watch until you see some curdling or coagulation, then refrigerate and/or freeze. The bacteria produce lactic acid from lactose and the acid sets the milk. So if you let it set too long the whey will start separating and there will be too much acid. You can still use it, but the culture is weakened.

When you make some, you can always use a little fresh and freeze the rest.

[Scarlet Runner]

Well, you've got me pegged: no pH meter... yet!!

I'll figure out what temps are ideal for culturing my particular strains and go with that. And, I think I will plan to do exactly as you say: make a primer culture, use as much as possible over 2 weeks, and freeze the rest. From linuxboy's clarification, it's nice to know that I am doing the best I can by using it fresh, and then second best frozen- AND getting the most mileage from my initial DVI powders. 

Thanks so much!!

[linuxboy]

If you keep a culture for two weeks, make sure you progressively use more to ensure you're adding the same amount of live, viable cells. After 2 weeks, there will be about 20% cell death from the initial population if you store immediately at max saturation (pH 4.6 for meso, pH ~4.1 for thermo) at 34F.

[Scarlet Runner]

Hmmm- good point. I imagine cell death in the freezer (my freezer, not a minus 80!) would be comparable? Or perhaps greater than 20%, not as much dependent on time frozen but rather on the act of freezing itself?  So maybe I should use all I can fresh and simply freeze the rest immediately...

[ArnaudForestier]

Hate to throw a wrinkle in this, esp. if I'm wrong (likely ), but if the point of a primer culture is to achieve something of a known inoculation rate with culture already rocking, without doing viability counts under a scope, wouldn't the dropoff itself be a variable, with variable death rates among the strains, yielding an overall variability perhaps making moot the point of priming, anyway? 

I guess I'm asking after practicality, if one isn't producing large batches, and that daily.  I definitely appreciate the value of a primer culture - most especially, the virtual absence of lag time, or at least one significantly reduced, when compared to DVI; but wonder if the potential costs in storing unused primer over using "fresh" DVI powder may negate the benefit.  Thoughts?

[linuxboy]

cell death in the freezer (my freezer, not a minus 80!) would be comparable?

Much slower, especially for the first several months.

not as much dependent on time frozen but rather on the act of freezing itself?

Both. If you freeze very slowly, so large ice crystals form, that's not as good as freezing very quickly. And then the time in the freezer and freezer temps matter. They're all variables.

wouldn't the dropoff itself be a variable, with variable death rates among the strains, yielding an overall variability perhaps making moot the point of priming, anyway? 

Point of priming is to make a fresh batch every 1-3 days, making the inoculation the same.

potential costs in storing unused primer over using "fresh" DVI powder may negate the benefit. 

That's why you make up small batches of primer according to your anticipated cheesemaking schedule. For example, are you going to have 3 makes over the weekend? Then make enough primer to last, and then the next weekend (or whenever), make some more from scratch.

[ArnaudForestier]

Gotcha, sorry, I haven't read these 2 threads closely enough, and missed the essential point - forgot the provisioning for primer culture/batch milk ratio, and setting up for whatever batch one wants to do; that's it's not about setting up for large batches only. 

Won't need the induction, have yet another use for Yoav's roaster-vat.

[linuxboy]

Yep, right. I've used this technique for years as a short cut to true mother culturing so I can still use my mother culture recipes, without having to reculture every day like factories do. That's the history of this method: a sort of hybrid between old-style culturing from a known mother, and straight addition of lyophilized culture. You get the benefits and consistency of DVI with the benefits of mother cultures.

[ArnaudForestier]

Yep, right. I've used this technique for years as a short cut to true mother culturing so I can still use my mother culture recipes, without having to reculture every day like factories do. That's the history of this method: a sort of hybrid between old-style culturing from a known mother, and straight addition of lyophilized culture. You get the benefits and consistency of DVI with the benefits of mother cultures.

I am looking for it, Pav, as I think I saw it somewhere - but is there something of a conversion calculator, for replacing this sort of primer culture, v. using a straight DVI inoculation?  In other words, and this may be too nitpicky, but what I would love to find would be something of:

- a culture population optima for any of different cheeses (most immediately, for me, would be tomme, and reblochon); or a more quick and easy for families of cheeses (as I am currently learning on, and will have to re-read to soak in - strategies for early pH changes, to achieve later changes).  I know this can be loosely derived from multipliers, but interested in something more specific;
-Having that population optima, a means to estimate what a straight DVI inoculation would yield, and primer culture would yield.  So that "1.5%" would be a good primer inoculation, for a given cheese, and ".75" for another.

Am I asking it clearly/correctly?

[linuxboy]

Yes, I've posted it before.

http://cheeseforum.org/forum/index.php/topic,5691.msg41618.html#msg41618

Not sure what you're asking for the first question, exactly. Population optima in terms of CFUs/g per lb of milk for each cheese style and how that translated to bulk %, DCUs, and Us?