It's the Little Things That Can Slow Down Fermentation Time in the Vat

Recently a plant made me aware that one of their cottage cheese cultures was having a longer fermentation time in the vat, even though it did not show that it had any phage hits on it when sending in the vat cheese whey for bacteriophage susceptibility. It had been going on for a few weeks (or the last several times that they had used that culture strain number). What was going on here??

I was visiting this plant as part of my normal technical service routine and noticed several (little?) things that could be contributing to the problem. I will discuss those things below.?

1.??? As I mentioned in a previous technical bulletin, cultures are a living thing and must be treated as such. Things such as storage conditions and pellet integrity must be evaluated to make sure you are adding 100% live and active cultures to your cottage cheese skim milk fermentation vat. Therefore, the first thing one might ask are, “Does the culture bags show any signs of thawing and re-freezing into a mass of fused together pellets which look like an ice slab or chunks of culture in the bag?” That means some of the pellets are not “free flowing” anymore but have been fused together by thawing during shipment or handling and refrozen into the chunks or slab form. If the bag IS NOT free flowing and does not break apart easily into pellet form, you can be assured you ARE NOT dealing with 100% live and active cultures! So, the question becomes how much of the bag have been damaged? One third, one half, two thirds, or all of it??????????????????????????????

So, let us say you estimate 1/3rd of the bag has fused together into bigger chunks. When this happens cell death occurs because the larger ice crystals that are formed during the re-freezing process after thaw, actually puncture the cell walls of the living lactic acid bacteria and kill the cell. Let’s say you normally use 4 bags of culture to set a 4000-gallon vat of skim milk. Estimating a third of activity loss of the bag means that now you are really only setting the vat with 2.6 bags of live and active culture! (4 bags x .33 = 1.32 less bags added due to culture death. 4 - 1.32 = 2.7 bags of live and active culture). And you wonder why your fermentation time in the vat is slower! You need to account for that loss of activity and take that into account. Add an extra bag or two for loss of activity (or more bags).?

2.??? At this particular plant, they do not use any anti-foam (or defoamer) in the cottage cheese skim milk as the vat is filling. This was evident by observation right at the plant itself. Cultures do not like air. They are microaerophilic and tolerate some air, but they prefer to grow in anaerobic conditions, not with lots of air dispersed in or floating on top. This will slow down fermentation time in the vat. Use some anti-foam!?

3.??? The air temperature in the room can be too cold cooling the surface of your cottage cheese skim down! Cultures have a specific optimum growth temperature range. For mesophilic bacteria this is between 91-92F. The room temperature in this cottage cheese operation is set at 63F. Thermometers exposed to the air showed a temperature of 61.8F and 65.4F behind the vats. This has cooled the top layer of skim from set temperature of 94F down to 87.3F after 5 hours of fermentation. This is out of the mesophile’s optimum growth temperature range. Covering the vats with food grade plastic wrap will at least help hold in the vat temperature some (closer to the 94F set temperature) and function as a deflector shield for cold air blowing on the cheese vats. This condition is also contributing to a longer fermentation time.?

4.??? Other general questions to ask yourself might be as follows. Has there been any phage hits on your culture previously? Are you doing any construction in the plant? When was the last time you chlorine fogged the atmosphere in the room in order to kill the bacteriophage? Have you rested a strain recently and the culture in the freezer has aged another two to four weeks? If so, and you bring the slow culture back, you had better add an extra bag or two to account for activity loss in your storage freezer. Culture is way cheaper than a vat of lost skim, so you might be very glad that you did! As you can see a lot of “little things” can all contribute to increased fermentation times.

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