Pressures confusion

[Gobae]

I'm getting a cheese press built and I need to know the range of PSI it should be able to handle. Now, I've done some searching through the forum and although I see this question asked repeatedly, by the time I get done reading the thread it seems the replies contradict themselves.

So then I decided to look through a couple of the cheese books I have: ( "Artisan Cheese Making at Home" and (B) "200 Easy Homemade Cheese Recipes". Book A is quite clear that the weights they recommend are NOT given in psi. In other words they are not dividing by the surface area of the follower. Book B is also quite clear that the weights they recommend ARE given in psi. But when you convert book A into psi the differences are extreme.

Here's an example of both book's Parmesan recipes.

A - Press @ 10# for 30 min, then press @ 20# for 12 hours. The recipe specifies a 8 tomme mould to be used so that means .19psi for 30 min then .39 psi for 12 hours

B - Press @ "medium pressure" (the book defines this as 10-20psi) for 30 minutes, then "very firm pressure" (the book defines this as 40-45psi) for 12 hours.

As you can see the differences are massive. So what PSI should I be looking to press hard cheeses at? Fractions of psi, or 40-50 psi?

Thanks!

[pastpawn]

(B) must be using pounds force, not pressure.  It's common for people to misuse these.  I do all the time   It's inexcusable in a technical book, of course. 

Here are the errata for the first book.  You might check for the same for the second book. 

http://www.artisancheesemakingathome.com/pdfs/ACMH-CORRECTIONS.pdf

I can't answer your final question since I unfortunately have screw-type press and can't know the pressures.  Ugh. 

[smolt1]

Have you read this  https://cheeseforum.org/forum/index.php/topic,6926.0.html ?

[Gobae]

Have you read this  https://cheeseforum.org/forum/index.php/topic,6926.0.html ?

No I hadn't until you linked to it, but that doesn't really address my question(s). Those examples only go to cheddar at 11.35psi.

I really need to know what the upper range of psi I'm looking at so I can have a cheese press designed/constructed appropriately.

[awakephd]

Gobae, you have identified one of the major flaws (IMHO) with book B. For the most part, I find the recipes very good, but the psi figures given seem to be way, way too high. I've wondered if there should be a decimal point in there -- 2.0 psi rather than 20 -- or whether the author is using a press driven by air pressure. If the latter, the actual psi delivered to the press is NOT the same as the psi delivered to the cheese. (If we were talking about a hydraulic system, it would be a different matter.)

As a reference point -- the greatest amount of weight I have used on a 3-gallon make in a mold that is just under 7" in diameter is 150 lbs. That works out to a little under 4 psi. Others may have a different experience ...

[John@PC]

I agree with awakephd about the upper limit, but if you search through the forum you will find there is a wide range of opinions.  I think Karlin's book has a max of 40 lbs force or so (max 7" dia molds).  Personally I have never had to go above 100 lbs for an 8" mold (except for my 2kg Gouda Kadova mold where I do go to 130# on the final press).  Because they're so many variables I would suggest using the recommending pressing schedule as a guideline and just monitor drip rate and how well the curds are consolidating as whey is expelled.  I would ditto 150 max. and that will get you an ample 4 psi with a 7" dia. mold.

[Spoons]

Hi Gobae,

Here's what I do and it works really well for me. Part of it is based on Caldwell's book.

First press for any type of pressed cheese:
gradually and very slowly add weight until you see whey slowly dripping out. This step can take about 1 minute of adding weights. I have 0.5LBS weights and I add one at a time and wait a few seconds before adding another. I stop adding weights once it starts dripping. The dripping can sometimes kick in 10-15 seconds after adding a weight, so be patient. Results vary even when making similar cheeses.

Second press for any type of pressed cheese:
Same as above, but it takes more weight to see the whey slowly drip. Usually around 1-2psi

Third press Semi-hard cheese:
3.5 to 4 psi does the job at 22C ambient temp.

Third press milled cheese (cheddar):
Still figuring that one out. 4-6 psi isn't enough... Well, it's enough but you'll see some cracking during drying. I'm hoping 8 psi will give me better results next time I try.

[John@PC]

Nice explanation Eric.  Milled cheese is in a class by itself and I did have one crack so maybe that was the reason.  I saw a video (would link if I could find it) of a creamery that milled it's cheddar with what looked like a meat grinder into small bits and pressed with ######s of pressure (sorry, can't remember but it was up there). 

[Gobae]

Many thanks for these responses. They are serving to give me a good indication that book B's 40-45psi is way too high to be accurate and what a more reasonable psi range might be.

The "Project Lead the Way" engineering students at my school are designing and building a press (two actually) for me and we need to determine the psi criteria. And since I don't currently have a press I wasn't sure what max psi would be reasonable.