Fruit and Veggie Puree in tank "too" long

Hi all,

Looking for some thoughts and advice on this.

Working in batching and packaging fruit and veggie purees of various types and formulations, we make batches (4000 lbs - 6000 lbs) which are then packaged into small individual containers.  It is all high acid or acidified to less than 4.2 and most typically less than 4.0 pH.  We have situations where after a 6-8 hours the pH increases above 4.2 and inceased by 0.2 pH from the beginning of the batch.

Do you guys and gals have any thoughts as to why this may occur?

Thanks

Hi, Akiel.

​might be better if to provide further details, e.g. storage temp and/or  is it in storage tank where the pH changes?  I assume that it is coming from heat treatment (not UHT), thus if your storage is favorable for microbial growth, this may then result to change in pH overtime.

Thanks

Hi Akiel,

Do you have continuous stirring/agitation of the tanks during the process?
If not then you'll almost certainly find some settling occurring, and this can create a gradient from top to bottom of the tank for pH, Brix etc.

If you don't have any stirring mechanism within the tank(s), you can gently pump the product round on a loop out of the bottom and back into the top and it will help reduce this effect, but you'll potentially introduce a lot of air into the material and depending on what you're processing and what it's used for this can create other issues (e.g. significant increase in the rate at which browning occurs).

How sure are you that you're achieving a uniform blend when you're acidifying the products?

With pulpier materials like purees it can be more challenging to ensure that the acidifying agent is really evenly distributed throughout the batch. If you've got a tank that'll let you sample from multiple points, or a long "dipper" you can use to sample at multiple depths, then this could also be worth further investigation just to rule it out.

Lastly, if you're pureeing the material yourself as part of the same process, it could be possible that some of the fibrous structure of the fruit/veg is still being broken down in the tank, and this will release further materials into the liquid phase with a consequential effect potentially both on overall acid content and buffering capacity, and thus the pH.

Thanks for the replies.

There is a heat treatment applied to the product.  The tank is heated to about 100 F and then pasteurized as it goes to filling to 207 F.  Product returns to the tank if the fillers are not running.  We find the pH change in the tank.  We have historical data that would say that the product was at or close to equalibrium pH at the starting.  The tanks also do have stirring/agitating blades that constantly run.

I suggest you perform some more pH monitoring of the tank and finished good post packaging. Perhaps the acidifier is not sufficient in it's amount to hold your pH long term?