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GENERAL CHEESE MAKING BOARDS (Specific Cheese Making in Boards above) => STANDARD METHODS - Forming Cheese => Topic started by: sstrantz on March 01, 2011, 02:12:32 PM
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I have a question regarding pressing weight vs. psi.
Up till now most of the recipes I’ve used have stated lbs. rather than psi (and I have a formula to convert it for different size molds) so this hasn’t been a problem. When I got 200 Easy Homemade Cheese Recipes the weights are stated in terms of “light pressure, medium pressure or firm pressure”, relative to psi.
For example, in the 200 easy Homemade Cheese Recipes book, page 37, it states the following:
Light pressure = 5 – 10- psi
Medium pressure = 10 – 20 psi
Firm pressure = 20 – 45 psi. or higher
I have the chart from this link: http://cheeseforum.org/forum/index.php?action=dlattach;topic=6423.0;attach=11420 (http://cheeseforum.org/forum/index.php?action=dlattach;topic=6423.0;attach=11420)
But I’m not sure I’m interpreting it correctly.
So, let’s say I’m using a 6” follower and the recipe requires “medium pressure”. The list from “200 Easy…” states medium pressure is 10 – 20 psi. If I’m interpreting the chart correctly from the link above, that would be anywhere from 300 lbs – 550 lbs of weight.
Am I interpreting that correctly? (That sounds like way too much weight and way more than even some of the higher weight Dutch Presses would handle that I’ve seen that will go to about 250 lbs.)
Thanks for your input…
~Sue~
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Sue I believe that you are reading the chart correctly. A 6 inch diameter requiring 20 Psi would require ~550 lbs. I don't know if you have the formula for calculating Psi when using a dutch press so here that is:
Dutch Style Press Calculations
Mechanical Advantage (MA) = Total Arm Length / Distance from Plunger to the Fixed Point in the back (fulcrum)
Weight Applied = MA * Weight + (Weight of the Arm and Plunger)
So all you have to do is apply those calculations to the press you are using.
A lot of the recipes that you will see are adapted from commercial processes that are able to supply the huge Psi values that you will often read about. Post the type of cheese are you making and I'm sure you will get some feed back about Psi values that you will be able to comfortably use.
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If I'm not using a dutch press, but instead I'm applying the weight directly on top of the follower how can I calculate the PSI???
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Sue
You first need to figure out the area of your follower and then using that number you can determine PSI or weight needed. For a circular follower the formula for area = radius squared by Pi ( which is 22/7 or approx 3.14) so your 6 inch diameter follower has a radius of 3 and an area of 3x3x3.14 = 28.26 square inches.
Using that number you can determine that if you want to press your cheese at 10 PSI you need to put (28.26 x 10) 283 lbs of weight on top of the follower. Conversely, if you decide to put only 100 lbs of weight on top of the follower you are pressing at ( 100 / 28.26) 3.54 PSI.
So you can see why people use a Dutch style press because the mechanical advantage of the press allows using a smaller weight. I would research the site for more discussion as trying to put 300 - 500 pounds on top of your follower can be unsafe as some members have attested. There is also discussion on the site about different ways to mold your cheese without requiring high PSI.
Good luck
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Wow! No wonder so many of you use a Dutch Press or something similar!
I guess a Dutch Press has just now moved higher on my "want list".
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Thank you Chris I think I'm going to make my own dutch press
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I would research the site for more discussion as trying to put 300 - 500 pounds on top of your follower can be unsafe as some members have attested. There is also discussion on the site about different ways to mold your cheese without requiring high PSI.
Would you be able to add a link that would direct me to some of the posts you reference above?
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Hi Sue.
Yes those figures do sound pretty huge don't they? :) Just something to consider a typical medium size Dutch Style cheese press will give you about a 5 times MA (Mechanical Advantage) if you add 4 -5 pulley strings that will add another 4 - 5 MA. So up to 10 MA. That means with a mere weight of 50lbs you can generate 500lbs at the follower. Now whether your follower can take it or not is another question. :)
As your wheel sizes increase so does your need for higher pressure. Some people like RenaissanceMan resolve this problem by building a Large size Dutch Style cheese press. The you just have to find the hoop/mold and follower that will take the pressure. I believe Ulmers sell Stainless Steel hoops and I guess you'd have to make your own follower.
Would you be able to add a link that would direct me to some of the posts you reference above?
If I'm not mistaken he may be referring to "prepressing" or "pressing under whey". Either of these search terms should get you to those posts.
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...or for home or hobby cheese making, don't feel particularly obligated to match commercially-sized hoops. Using a smaller hoop dramatically reduces the amount of weight you need to work with, and that means your press can be dramatically lighter than a commercial press capable of handling huge pressures. Unless you are selling your cheese commercially, I can't see the advantage of processing such large numbers of gallons of milk at once either.
Brian
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Somehow something doesn't seem to add up. In the 200 Easy Cheese recipe book, the author lists the psi as I stated in the first post above, then in the next paragraphs begins to describe how a brick can achieve the lower pressure and a block can achieve the medium pressure.
It seems she may be jumping from psi to direct weight in her description.
In the recipes, the only press weights she states are light, medium, etc. Which, I thought, referred me back to her psi charts.
If she IS referring to psi, the pressing weights don't sync at all with the pressing weights required in the Ricki Carrol book - even with adjustments for diameter (for which I have another chart related to direct weight).
So...is it possible that the author is referring to "direct weight" in her recipes rather than psi?
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Weight or PSI is recipe specific. I do remember a Wisconsin cheese that I saw called Brick Cheese. The dairy used bricks, and has been using the very same bricks, for generations.
Cheese like queso Blanco, a brick will suffice as well, cheddar, I'm up to 20PSI on an 8" mold and thinking I may need more.
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Just remembered this question was raised in the Book forum about this book. Here's a link to it:
http://cheeseforum.org/forum/index.php/topic,1786.0.html (http://cheeseforum.org/forum/index.php/topic,1786.0.html)
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Could Debra be quoting the line pressure of her pneumatic press and not the psi on the follower?
She stated:
We have a pneumatic press which we can set at different psi. Start out with a light press of about half the weight of the cheese, so if you have a 2 kg cheese you can go with 2 psi to get started. For a larger cheese, a light press is 5 psi. Increase gradually.
I just received my pneumatic press which has a multiplier of 5 times, so if I use 2 psi line pressure it is 10lbs of weight on the follower. So on a 7" follower that is 0.26psi.
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Could Debra be quoting the line pressure of her pneumatic press and not the psi on the follower?
She stated:
We have a pneumatic press which we can set at different psi. Start out with a light press of about half the weight of the cheese, so if you have a 2 kg cheese you can go with 2 psi to get started. For a larger cheese, a light press is 5 psi. Increase gradually.
I just received my pneumatic press which has a multiplier of 5 times, so if I use 2 psi line pressure it is 10lbs of weight on the follower. So on a 7" follower that is 0.26psi.
Yes, Mikeradio, I think you may be correct! The numbers you are stating make better sense. Especially since they correlate and actually match all the other recipe books and single recipes for home cheesemaking batch & mold sizes that I've seen.
Can you explain, just so I have a better understanding, what is meant by "line pressure"? I see that the numbers match with other recipe books but I don't really know what that term means.
This is the first thing that has made sense to me since I've been pondering this question.
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Oh...and thanks, Kosherbaker. I did go and read that whole topic that you linked...and that is where I saw the quote from Debra that mikeradio quoted above. Appreciate the link!! :)
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Also another question for Mike...you chose the 7" follower (for .26 @ 10lbs) as a standard. Help me understand why.
For example, if you look at .26 on a 6" follower that would be between 5-8 lbs. So, How did you decide to start w/a 7" follower for the standard?
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Hey Leah's Mom
When you have a pneumatic (air) press, you have to feed it compressed air from a compressor or tank. So when I say line pressure, that is the air pressure in the line feeding the air press. My air press has a multiplier of 5 times, so if I apply 2 psi to the air press it multiplies by 5 and give me 10lbs press on the follower. If I apply 100 psi to the air press it is 500 lbs. If you don't have a air press you don't have to worry about line pressure. My follower is a 7" so that is why I used an 7" in my example, there is no real standard when it comes to this, you have to calculate the psi and lbs based on the size of follower you use. Hope this helps, this is always confussioning because most recipes do not state what size of follower they are using when they quote the press weights. I think most assume a 4" follower, so if you use a 4" follower you can use there weights, but if your follower is a 6" you need to increase the press weight to match the same psi on the 4".
Mike
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Line pressure is a term used only when a pneumatic or hydraulic cylinder is used and is the pressure provided to the cylinder by the compressor or pump. How much force this cylinder exerts on the cheese under that pressure is dependent on the area of the air cylinder itself. The bigger the cylinder the greater the pressure it applies. Don't get this confused with the psi dynamics we all discuss when we are talking about dutch presses. It can really get confusing.
She is defintely referring to line pressure and she must have a 2.5" cylinder. The "multiplier of 5" is simply the area of the cylinder being used. In this case the cylinder is a 2.5" diameter cylinder. That means that you are multiplying the line pressure (2psi) by the cylinder piston area (4.9 sq in) to get the total force applied (9.8 pounds).
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My last post was redundant after Mike's post but I had already typed it so I posted it. Good response, Mike.