Yogurt - Slimy Texture

[rips]

My yogurts are slimy. When taking a spoonful, long threads form on the sides, never breaking.

I use pasteurised milk, sometimes milk powder, and store yogurt as starter. The problem disappears if I use low-lactose milk but it is very expensive so I would like to find another solution.

Has anyone had (and solved) this problem?

edit: I should add that the low-lactose milk is also ultrapasteurised. Is it about sugar types or about competing bacteria from the simply pasteurised milk?

[MrsKK]

Hey, Welcome to the Cheese Forum!

Do you re-pasteurize your "regular" milk before cooling it to add the culture/store yogurt?

I've never made yogurt from store bought milk, having my own cow and lots of raw milk available.  Before I used the method I learned here, I had several batches that were slimey or really thin.  I wasn't consistent with my temperatures, as I was experimenting and trying to find something that worked well.

Then there was a great discussion on this forum about heating milk to 180-185 degrees Fahrenheit and holding it there for about 20 minutes before cooling it down to 100-110 degrees and then culturing it.  I've used that method ever since and have gotten good, thick yogurt every time.

Can you post the method that you use, as that might help us answer your questions better, too?

[rips]

I heat up the pasteurised milk together with a little powdered milk to 40-45C (104-113F) and then add the culture. The I keep the temperature there for 8-10 hours (home-size yogurt maker).

I see that your experience concords with mine. But I would like to understand whether it is related to lower lactose content in ultrapasteurised milk (or long-heated) or if it is about competing bacteria in the pasteurised milk.

[swh]

Rips,

I usually use one percent store milk and I will occasionally addsome dry powder (when I remember). I have always heated to 180 the cooled to 116 and add a couple of tablespoons from the previous batch and hold overnight. It's just the way I was taught and have since seen similar directions in several texts.  I started over six months ago with a packet of culture and have been going strong ever since making a half gal. every 5-6 days.

[FRANCOIS]

You need to heat to 165F minimum, 185F is better.  The success you had with low lactose milk is because it is ultrapasteurized, not because of the sugar content.  Scalding of the milk is required for yogurt (and ice cream) to denature (or "crack") the protein.

[Cheese Head]

Rips, welcome, I use store bought whole milk and same as MrsKK & Steve I've also found that I get much better results when heating milk to 180F and then cooling or just setting aside to cool than if I don't. When I didn't, I don't remember getting a stringy texture . . .

Francoise, now that's interesting, I thought by re-heating I was re-pasteurizing the milk to reduce competing bacteria and I couldn't figure out why given it was fresh store bought pasteurized milk. If you or anyone has time, any more details on denature/cracking the proteins would be appreciated.

[linuxboy]

Sure, John. The basic principle here is protein denaturation. This is when a complex protein "unwinds" and forms smaller strands. The heat cracks open the protein.

The two major proteins responsible here are lactoglobulin, and lactalbumen. What happens is that they crack at slightly different temps and different rates at those temps. The lactoglobulin goes first, and then the lactalbumen follows. When the lactoglobulin denatures, the strands of it bond to the casein micelle complex, specifically, to the outer k-casein "shell". This is not so cool, because micelles cannot bond well when that happens. This is why UP milk doesn't work for cheesemaking. Now after that, the lactalbumen steps in, due to the longer heat/time for yogurt-destined milk that UP milk typically doesn't undergo. The lactalbumen acts as a putty... it fills in the gaps on the micelle complex. With the micelles "smooth" again, the nature of the bonding changes. When I meant putty, what I'm really talking about are chemical bonds. Anyway, with the lactalbumen in place, the stage is set for the pH change, which drops the micelles out of solution and causes them to bond into a matrix that retains water very well.

Also, wanted to comment on the stringy texture. UP procedures are different, so two UP products may be very different in their chemical and salt makeups. Also, bacteria can form long chains or have long polysaccharide complexes in the outer casing, which could contribute to a "slimy" mouthfeel. This actually does have to do with the types of sugars and other food that the bacteria consume. Also some strains are more prone to chain forming than others, leading to ropiness. But with the heat treated milk, it is not an issue because you get such a firm curd set that retains water well.

In the end, if you want to replicate commercial products, follow commercial processes. For yogurt, that's 185°F (85°C) for 30 minutes or 203°F (95°C) for 10 minutes. 165 is not terrible, like Francois said, but you have to cook it  longer.

[rips]

Thank you all for great answers.

As both milk types (pasteurised and ultraP) will have to be heated up, I will opt for pasteurised milk, which is the cheapest and most readily available in Norway. Of course I will try something next time I visit my parents-in-law at their huge dairy farm...

Further question: we have several types of buttermilk made with mesophile bacteria. Will I need to follow the same heating procedure as for yogurt for the buttermilk to thicken?

linuxboy, I worked on blood coagulation a long time ago and I think I get precisely the matrix-thing. Is it actually a covalent gel?

[linuxboy]

rips, are you asking if fibrin covalent cross-linking is comparable to casein micelle bonding? Yes, but of course the blood coagulation cascade is much more complex.

[rips]

I have to report a great success! I followed the forums advices and my yogurts were beyond all expectations! By far the firmest texture ever and without powdered milk! I'll just have to fine tune the heating so I loose no time in overheating/cooling.Thank you very much.

[MrsKK]

I'm so happy we could help you find success in yogurt making.

What are your plans for your next dairy adventure?

[rips]

I have just put a jug to ferment while I'm at work, to use as buttermilk, and another liter of the same culture (Lactobacillus acidophilus La-5, Bifidobacterium Bb-12) to make a kind of cheese this evening. Can you suggest cheeses these bacteria are adequate for?

[Cheese Head]

linuxboy

• Thanks for the detailed response! I've read it three times and I think I understand what scalding or pasteurization does to the milk's structure ("unwinds" or "cracks" complex proteins to form smaller strands) in addition to killing off microorganisms.
• But why do I need to do this when using already pasteurized milk from store to make yogurt or ice cream?

rips

• Buttermilk is a common mesophilic starter culture, I've used store bought buttermilk many times for making several cheeses. To use it it needs to be concentrated and thus thickened just follow these simple steps, no high heating. If you haven't made cheese before I'd recommend using it to make simpler cheeses such as Cream Cheese or American style Neufchatel (light cream cheese) or Feta.
• I've never left a jug of milk to ferment naturally, I think that's how you make clabber, not buttermilk, there are couple good threads here on making clabber to be used as a mesophilic starter culture.
• Those two microorganisms are Thermophilic lactic acid producing starter cultures, often used in yogurt (see ingredients picture) and can be used in high heat cheese making recipes, recommend look in the Hard Cooked & Hard Grating Type Cheese Boards for ideas of what cheeses it could be used for.

Some info here on meso vs thermo starter cultures.

[rips]

John (CH): when I said "put a jug to ferment", I meant with store-bought buttermilk. I wouldn't dare leave milk on its own (though I've done it with bread dough counting on wild yeast...) And I did the concentration routine But now I'm wondering if the other jug meant for cheese making will be too fermented (10 hours at room temperature).

linuxboy:

rips, are you asking if fibrin covalent cross-linking is comparable to casein micelle bonding? Yes, but of course the blood coagulation cascade is much more complex.

Yes, that was my question: whether "yogurt bonding" is covalent as opposed to "weak". And for the coagulation cascade, though very complex, I can't remember if it plays a specific role other that producing the actually reactin molecules.

[linuxboy]

But why do I need to do this when using already pasteurized milk from store to make yogurt or ice cream?[/li][/list]

Pasteurization and high heat treatment are not necessarily the same thing. Whereas a high heat treatment fulfills the PMO regs for pasteurization (30 min @ 145F, 15 secs @ 161F, etc), it is held for a lot longer and at higher temps. So ordinary pasteurized milk is much more intact than milk that has been scalded for yogurt. Even UP milk may not work as well because with UP milk, the lactoglobulin may be mostly denatured, but it takes longer for lactalbumen.  One key aspect here is time. So UP milk treated for a few second at ultra high temps doesn't work as well as heat treated milk.