### Author Topic: pounds or psi...I'm so confused  (Read 1649 times)

#### Jeepyj

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##### pounds or psi...I'm so confused
« on: May 18, 2015, 06:23:34 PM »
Since this past weekends cheese disaster turned experiment, I'm still determined to make pepper jack. I have three 'recipes' for pepper jack that all end up with

" Press at 3 pounds of pressure for 15 minutes.
Take the cheese out of the press, unwrap and flip it, rewrap it and place it back into the press at 10 pounds of pressure for 12 hours."

For the 3 pounds "of pressure", do i put a (roughly) half gallon of water on top of my mold to make 3-4 pounds or do I put 150 pounds of weight on my 8" diameter mold? Seems like theres a little difference there.

#### smolt1

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##### Re: pounds or psi...I'm so confused
« Reply #1 on: May 18, 2015, 06:48:57 PM »
Some of the authors of cheese making books are also very confused. First there is no such thing as pounds of pressure. pounds is a measure of force(weight) not pressure ( PSI....Pounds per square inch ). For your specific problem, The intent of the recipe is probably to press with 10 lbs of weight. To get 10 PSI of pressure on an 8 inch mold you would need 502 lbs of weight.

#### Jeepyj

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##### Re: pounds or psi...I'm so confused
« Reply #2 on: May 18, 2015, 07:04:12 PM »
probably?

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##### Re: pounds or psi...I'm so confused
« Reply #3 on: May 18, 2015, 08:09:56 PM »
I have found that the best way to go about this is to determine what mold is the author using and how many gallons is the recipe for and determine if the author meant PSI or actual pounds of pressure.  It is unlikely that the author meant 10 PSI because you would need to apply 10 pounds per square inch computed as

For your mold it would be 3.14 times 4 times 4 which would total 50.24 square inches.  If the author meant 10 PSI, indeed you would need to press at 502.40 pounds.

When in doubt look at the whey coming out of the pressed cheese.  If it is very cloudy back off the weight / PSI.  The purpose of pressing is to remove the weigh and fuse the curds but not to compress them to the point that you would expel the good stuff.

#### OzzieCheese

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##### Re: pounds or psi...I'm so confused
« Reply #4 on: May 19, 2015, 12:00:27 AM »
For a Jack the force seems about right  - if not a little light on.. I would press it between 8-10 pounds between two planks if you like a rounded cheese for 6-8 hours.  The main aim is to both encourage the whey out whilst retaining enough so the lactic acid builds up and the rind closes.  Dont over press otherwise it tends to end up dry and not very tasty.

-- Mal

#### Jeepyj

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##### Re: pounds or psi...I'm so confused
« Reply #5 on: May 19, 2015, 07:02:00 PM »
Thanks everyone. I won't be a noob forever.

#### Raw Prawn

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##### Re: pounds or psi...I'm so confused
« Reply #6 on: May 20, 2015, 03:30:41 AM »
I think the best approach is to treat the values given in recipes as guidelines and experiment a bit and this.....
When in doubt look at the whey coming out of the pressed cheese.  If it is very cloudy back off the weight / PSI.  The purpose of pressing is to remove the weigh and fuse the curds but not to compress them to the point that you would expel the good stuff.
... is probably the most important guideline of all.
I would suggest that if you are unsure, err on the side of a lighter weight. If you don't get a good knit, increase the weight and/or the pressing time.
The heaviest pressure I've used was about 6 PSI on a Cantal and that was enough.
- Andrew

#### podgida

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##### Re: pounds or psi...I'm so confused
« Reply #7 on: June 25, 2017, 03:25:59 PM »
So, now I'm confused. I've been trying to figure this out for weeks. I've read hundreds of threads on this forum regarding this very topic. And I'm still no closer to figuring this out. The book I have is 200 easy homemade recipes. It specifically states to press at 20 PSI, which for my 6 1/4" mold would require me to hang 156 LBS of weight off of the end of my Dutch Cheese Press in order to apply 624 LBS to my follower. So If that is not the case please let me know as applying 20LBS at the follower would be so much easier.

Thanks

ps I'm really not sure about posting in this forum. Apparently necroposting is frowned on. This was the newest thread on the topic. As posting a thousand different threads on the same topic is equally bad. So with no actual new threads on the forum you end up stuck in a situation where you can't post any new threads and you can't post in any existing threads. So I am not sure are we allowed to post comments at all? I've never heard of a forum that wants to die.

#### John@PC

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##### Re: pounds or psi...I'm so confused
« Reply #8 on: June 25, 2017, 05:35:21 PM »
Apparently necroposting is frowned on.
I'm not sure what the policy on this forum but my guess is that if you're dead posthumous posting may be frowned on.  Then again we fans of George Noory (Coast to Coast radio show) would love to answer questions from the "other side".

With that out of the way (and sincere apologies in advance)I personally don't have the the book you refer to but I would agree 20 PSI is a lot of pressure.  Personally I like to follow the advice of RawPrawn and "use enough pressure to get the job done" instead of "pressing by rote".

#### awakephd

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##### Re: pounds or psi...I'm so confused
« Reply #9 on: June 25, 2017, 08:18:24 PM »
Hi Podgida, and welcome to the forum!

The psi issue is known problem in the 200 Easy Cheese book. The key is to look carefully at the context on p. 41 - just before she says, "light pressure is 2 to 10 psi; medium pressure, 10 to 20 psi; and firm pressure, 25 to 45 psi." If she actually meant psi on the cheese, that would be insanely high - 10 psi is more than most people would use on any cheese, and even for a Cantal - which infamously needs a LOT of pressure to knit - 20 psi would be very high.

But look at the paragraph just above - "In a pneumatic press, a piston is driven by force supplied by compressed air ...." Aha! In the paragraph I just mentioned above, I think she is talking about the psi of the compressed air, NOT the psi at the cheese. Unfortunately, just a bit further down the page, she discusses the calculations to determine psi on the cheese, based on weight applied to a given diameter cheese. I can't decide if she has confused the two, but it is awfully hard for the reader not to make the natural assumption that psi in the pneumatic cylinder equates to psi on the cheese - but they are most definitely NOT the same thing, UNLESS the diameter of the pneumatic cylinder happens to be identical to the diameter of the cheese.

Unfortunately, to further complicate things, she neglects to mention what size of pneumatic cylinder she has in mind. A pneumatic cylinder of 2" diameter would give a surface area of π · 1² = 3.14 square inches. So 10 psi applied to this cylinder produces the equivalent of 31 lbs of weight applied to the cheese. (How much psi that would produce on the cheese depends, of course, on the diameter of the cheese.) However, a pneumatic cylinder of 4" diameter would give a surface area of
π · 2² = 12.5 square inches (approximately), so 10 psi of air pressure would apply the equivalent of 125 lbs of weight - quite a considerable difference!

So ... the formulas get very confusing, and the books often leave out crucial information. Andrew's (Raw Prawn's) and John's advice is a bit hard for the beginner, because you don't know whether you are seeing what you should be seeing - but really, it is the best way. With a little time and experience, you will quickly find what works best for the types and sizes of cheeses you are making. One quick hint: for hard cheeses, those that go into the press unsalted, with a relatively high pH, generally need light pressure to achieve a good knit, so you need to start especially light at first (e.g., Asiago, parmesan, etc.). Cheeses that go into the press after cheddaring - lower pH, salt added - need a LOT more pressure to achieve final knit - but at the same time, you don't have to rush, because the salt has already slowed down the bacteria. So even with these it is best to start slow and work your way up until you get a good knit.
-- Andy

#### smolt1

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##### Re: pounds or psi...I'm so confused
« Reply #10 on: June 26, 2017, 11:19:47 AM »
A cheese for you Andy.

A page on sturdypress.com also graphically displays the relationship between weight and pressure .

#### awakephd

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##### Re: pounds or psi...I'm so confused
« Reply #11 on: June 26, 2017, 07:16:01 PM »
A cheese for you Andy.

A page on sturdypress.com also graphically displays the relationship between weight and pressure .

Nicely done - a picture is worth a thousand words! A cheese for you as well.
-- Andy