2 replies to this topic

[monisha]

Hello everyone, Hope you are well. I am calling on UHT and Dairy experts to help me, if possible,

We are experiencing a strange quality defect in our UHT milk product. The main symptom is a noticeable cheesy, taste. The defect is not present immediately after production but becomes detectable and progressively worse during ambient storage, in 2 months.

We also observed tiny, soft gel or curd-like particles visible upon close inspection or when pouring the milk.

The milk still looks normal in the unopened pack, but the gel particles become apparent when the pack is shaken or poured. No major separation, creaming, curdling or colour change has been observed.

 

> UHT Full cream milk, Stored at ambient temperature (typical warehouse 20–30°C).

 

We suspected proteolysis and conducted HPLC analysis of peptides. Our control sample and the complaint samples yielded similar results. So, we conducted Free fatty acid testing (Assuming lipolysis) and the results were identical. Furthermore, We conducted APC, T-Spores, Mesophilic aerobic spores and thermophilic org and all were within limits. 

 

Can anyone help me out? Unsure what causes this cheesy taste to develop. 

Also, having looked at examples of Gelling online, the product has not completely gelled at all. We found maybe 5 to 6 small pieces of gel as we poured the milk through the sieve. 

 

Any help in the right direction would be appreciated 

 

[GMO]

I'm not a UHT expert but my first thought was homogenisation issues. My "go to" easy reference for dairy is the tetrapak Dairy Processing Handbook (free online). Tetra Pak Dairy Processing Handbook | Tetra Pak United Kingdom (just enter your email address to access). But bless Tetrapak, I love them for this resource, they suggest an alternative theory and I think this ticks boxes for being likely. (Go to the UHT section.)

What are your somatic cell counts like on the milk you've been using and total bacterial counts? Are their parlous clean? Have the farmers been having any issues with mastitis? Have you had any processing delays before UHT or temperature issues before the heat treatment?

 

"Enzymatic activity"

"In addition to being governed by the natural creaming phenomena described above, shelf life can also be limited by enzymatic activity. Enzymes are active proteins that have the ability to cut other proteins into smaller pieces. This action will then lead to loss of the colloidal stability, causing sedimentation and gelation to occur. In addition, bitter off-flavours may develop. In milk, there are two main groups of enzymes: plasmin, which are indigenous enzymes originating from the cow's immune system, and bacterial enzymes produced by mainly Gram-negative (G-) psychrotrophic bacteria. It’s important to note here that the enzymes are produced in the raw milk, when the bacteria are still alive. After the UHT treatment, the bacteria are killed, but due to the high heat stability, the enzymes remain active."

 

"How much enzymatic activity remains in the milk after heat treatment depends largely on the severity of the heat treatment. In general, an indirect heat treatment inactivates more enzymes than a direct heat treatment. For example, in indirectly produced UHT milk, almost all plasmin is inactivated, and shelf life is mainly regulated by the bacterial proteases. While in UHT milk produced in a direct system, both plasmin and bacterial proteases remain active."

 

"The higher the raw milk quality, the less enzymes in the milk. This implies clean milking equipment, cooling of the milk directly after milking and as little time from milk collection to processing as possible. This is all to keep the levels of bacteria low and give them as little time as possible to produce heat-stable enzymes. Healthy cows are the most important factor in keeping plasmin levels in milk low."

Edited by GMO, 14 May 2026 - 05:41 AM.

[Tony-C]

Hi monisha,

 

It does sound like it could be enzyme related.

 

UHT milk can be so frustrating, I’ve found that problems caused enzyme activity tend to come from poor quality ingredients/old ingredients or reworking.

 

A few questions:

 

Is this a consistent problem?

 

Are you using raw whole milk as the only ingredient or reconstituting milk powder (or AMF & SMP) then processing it?

 

Are you reworking product?

 

Do you have micro results for your raw milk/ingredients before processing?

 

Kind regards,

 

Tony