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Equipment & Gear: Kitchen Scales
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Cooking For Engineers



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PostPosted: Wed Jan 04, 2006 9:46 pm    Post subject: Equipment & Gear: Kitchen Scales Reply with quote


Article Digest:
A kitchen scale is an essential tool in every kitchen. Most American kitchens have a set of measuring cups, but don't have a kitchen scale. Even though kitchen scales aren't that common to the American kitchen, Amazon.com still has over 200 scales for sale ranging from $7 to over $300. Is this a gadget that only perfectionist chefs and constant bakers need? No, give a good scale a try and you'll find that it's a better and faster way to cook.

A lot of people know that you should use a scale when baking. Baking is probably the only form of cooking where I can say is a science without people arguing with me. (Try saying "stir-fry is a science" or "candy-making is a science" without having the science vs. art discussion.) This is because just about every cookbook that covers baking discusses the importance of balancing acids and bases and precise measurements are of paramount importance when trying to transform a wet glob of batter into a glorious, fluffy dessert. To get precise measurements, we are told to toss out the measuring cups and use a kitchen scale. But is baking the only reason to use a scale?

Why Use a Kitchen Scale
The first and foremost reason is of course precision. Precision is how repeatable a measurement is. For example, if we measured a cup of all-purpose flour in a 1 cup (8 ounces) dry measuring cup, we expect the mass of the flour to be 125 grams. Assuming that the dry measuring cup is constructed to strict standards, the cup is accurate but not precise. Every time flour is measured, it is a bit more or a bit less than 125 g. How tightly packed the flour is, whether it has been recently sifted, if we scooped the flour or spooned it, all make an impact to the repeatability or precision of using a cup as a measuring device. On the other hand, a scale is precise (and accurate if calibrated). When a cup of flour is weighed on a scale, it is possible to add or take away flour until the scale registers 125 g. The precision of the scale is dependent on how easy it is to read the scale. In baking, using a scale to measure all the ingredients will ensure that you are following the recipe correctly (at least in terms of the proportions of ingredients). Using measuring cups could result in having a little more flour than leavening, etc.

Repeatability is a big reason why I use a scale. When I've figured out how much sugar to put into a recipe or how much butter is needed, using a scale means that next time I make the recipe it will have a greater chance of ending up exactly the same as I made it last time.

If precision and repeatability aren't motivating factors for getting a scale (and for most home chefs they don't sound too compelling), here's a good one: faster measuring. No more scooping with a measuring cup and then leveling the top with a straight edge. Simply pour into a bowl set on the scale and stop at the desired point. With fast response digital scales, the weight display is updated fast enough that you can pour until you hit the desired value. Then you can zero out the scale and measure your next ingredient in the same bowl. Less mess to clean up, faster measuring, and more precision. There are no drawbacks to using a kitchen scale (except perhaps the initial impact to your wallet).

Types of Scales
There are three main types of scales available for use in the kitchen. Balance, mechanical/spring, and digital. The three operate on different principals for measuring weight. The balance operates by performing comparisons between known masses and the object to be weighed. (Technically, a balance determines mass not weight and is the only type of scale that will work properly if you plan to cook on the moon. The balance in all other disciplines is considered separate from a scale, but in cooking we lump the two together.) The problem with the balance is that it only reports if the object you are measuring is greater or less than the known mass. For example, when using a balance to measure a cup of flour, 125 g of known mass is placed on one side of the balance while flour is placed on the other side until the mass on both sides are in balance. [IMG]A beam balance has a beam with adjustable masses that move along the beam to increase torque applied to counteract the torque on the other end of the beam from the weight of the object being measured. (Exactly like the physician's scale at your doctor's office.) In general, a good balance is extremely accurate and can be extremely precise, but no matter how skilled the operator of the balance is, I feel it's a bit slow for use in the kitchen.

Mechanical scales use a platform mounted on a heavy spring to measure weight. An ideal spring compresses proportionally to the force applied to it. This means the weight placed on the platform is directly related to the distance that the platform moves down. The problem is that in actuality, springs aren't ideal. [IMG]For the most part, they do exhibit the property of linear compression, but they also may change compression rates over time, may not return to their original length, and sometimes even break. Also, another problem with springs is that small quantities are harder to measure than large quantities. For example, if a scale is designed to measure up to 5 lbs. then then measuring one ounce of something will be more difficult than one pound. This is because the small amount of movement in the spring caused by one ounce will be difficult to detect because the scale is designed to move evenly throughout the whole five pounds. However, high quality mechanical scales can be quite precise, but they also carry a hefty price tag. [IMG]Cheap mechanical scales can cost less than $10, but aren't terribly accurate or precise, but if these scales are the only ones you can afford, purchase a set of dry measuring cups instead. Properly used, the dry measuring cups will be more accurate and precise than the sub-$10 scales.

The final option is the digital scale. These scales range from $25 to over $100 with the vast majority in the $50 range. [IMG]A good digital scale provides easy to read measurements with high precision. They work based on an electrical component called a strain gauge (also known as a load cell). The resistance of the strain gauge changes based upon the compression or change in shape of the component. A simple computer in the digital scale is preloaded at the factory with a table of values that allows it to calculate the weight of a load by the change in resistance. Many scales update about once a second, but better scales will update their readings much faster. This means, if you're pouring sugar into a bowl, the scale will provide almost instantaneous feedback so you don't pour too much. Most digital scales also have a tare function that allows the user to subtract the weight of the container from the measurement.

Features To Look For
[IMG]A few months ago, WoodlandSprite directed me to Old Will Knott (retailer of fine scales) and the My Weigh i5000 Bowl Scale. I purchased the scale for $50 plus shipping and gave it a spin. This scale is well designed and is the perfect example of what features are important and how My Weigh managed to incorporate them. (Too bad I don't earn commission on the My Weigh i5000, because I'm about to explain why it's a great kitchen scale.)

Large Display - An easy to read display is important when measuring with a large mixing bowl on the platform. If the display is too small, it might be obscured by the bowl. Not only does the My Weigh i5000 have a large LCD display, a backlight turns on to illuminate the display so it's readable even if the shadow of the bowl is covering the display!

Avoirdupois (U.S.) and metric units - The ability to quickly and easily switch between U.S. (pounds and ounces) and metric (grams) units is useful when you have some recipes in grams and some in ounces. I receive some recipes that have both, so having a handy switch is a must. A few brands have their switches underneath the unit, so you can't switch while weighing. The i5000 has a nice button on the front that allows you to switch between grams, pounds and ounces (e.g. 1 lb. 8 oz.), pounds (e.g. 1.5 lb.), and counting mode (where the i5000 counts the number of jelly beans or whatever you put on the scale - which is, truthfully, the reason I bought the scale).

Tare - Taring is measuring the weight of the container. The tare function allows the scale to subtract the weight of the container and report only the net weight of the object being measured. Most scales allow you to repeatedly press the tare button, allowing you to measure many ingredients in the same bowl (e.g. measure flour, tare, measure sugar, tare, measure chocolate, tare, etc.). This is a wonderful feature and thankfully almost all digital scales have it. The i5000 also allows you to recall the gross weight (the actual weight) at anytime with a press of a button.

Seamless buttons - Some scales have buttons that are not, on the surface, formed from the same piece as the exterior of the scale. This means there are cracks where liquid or fine particles can get into and make cleaning a pain. Seamless buttons are a must especially if your fingers get dirty while working in the kitchen.

Removable bowl - Some scales have built-in bowls which makes cleaning more difficult and recipe preparation inconvenient. The ability to remove the bowl that comes with the scale (if it comes with one) and replacing it with your measuring cup, mixing bowl, or pot just makes everything that much easier. Although the i5000 came with a plastic bowl, I've never used it except to demonstrate to my friends the Jelly Belly counting trick.

Capacity - Most kitchen scales at the $50 price point measure up to 5 pounds (2.25 kg). This limits your ability to measure ingredients when using a glass mixing bowl or a pot which may weight a few pounds to begin with. The i5000 has an 11 pound (5 kg) capacity and manages to maintain a precision of 0.05 ounces (1 gram) throughout the range (most 5 kg scales have a 2 g granularity).

Recommendation
If you haven't guessed, my recommendation for a digital scale is the My Weight i5000.

The My Weigh i5000 can be purchased for about $50 plus shipping from Old Will Knott. It's a bit more expensive elsewhere.

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PostPosted: Wed Jan 04, 2006 9:47 pm    Post subject: Reply with quote

one thing I've always wondered about in using scales in the kitchen... what about humidity?
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PostPosted: Wed Jan 04, 2006 9:48 pm    Post subject: Reply with quote

With a good quality scale humidity is never a problem (unless it crosses over 99%...).
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PostPosted: Wed Jan 04, 2006 9:48 pm    Post subject: Reply with quote

I meant varying moisture content in ingredients, not the ambient humidity.
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Thomas W. Holt Jr.
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PostPosted: Wed Jan 04, 2006 9:48 pm    Post subject: Reply with quote

I was just watching America's Test Kitchen a few weeks ago and they had a rerun of their episode with the Equipment Corner clip on Digital Scales. Here's their recommendation. http://www.americastestkitchen.com/EquipmentCorner/751.shtml
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Stephanie
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PostPosted: Wed Jan 04, 2006 9:49 pm    Post subject: Reply with quote

Hi Michael Smile and thanks for the link. I'm still waiting for my trusty postal scale to kill itself so I can make my new digital scale purchase Big smile I bet you can guess which one I'm pulling for Wink
-WoodlandSprite
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PostPosted: Wed Jan 04, 2006 9:49 pm    Post subject: Reply with quote

Cool article about the strain gauge. I never knew about them. But if they also rely on some physical compression, won't the gauge also get worn out like springs do? Probably a lot less noticeable since it displaces far less than a spring scale.

You know what would be cool would be an computer automated mass balance. When you put a weight on, it automatically shifts the weights around to balance it. I bet you can this system extremely fast by fixing the "needle" instead of waiting for the seesaw action. The computer can just check when there was no pressure exerted by the needle to know when it is balanced. You can use the amount of pressure on the needle to calculate 1st and 2nd derivatives to make the balancing even faster. But someone's probably already thought of this already. =)
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PostPosted: Wed Jan 04, 2006 9:51 pm    Post subject: Reply with quote

Michael,
I've been looking to get a new scale. My current scale turns off way too quick...While I'm measuring stuff! (Very frustrating).
How long does the i5000 stay on before auto-off?
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Michael Chu



Joined: 10 May 2005
Posts: 1620
Location: Austin, TX (USA)

PostPosted: Wed Jan 04, 2006 9:51 pm    Post subject: Reply with quote

re: scales and humidity of ingredients
I'm not sure what you mean when you say humidity. Are you asking what to do if, let's say, the flour gets wet? Then the scale would not measure the correct quantity of flour (and for that matter, neither would measuring cups). Hmmmm... I'm not sure what to do in that case. Anyone have some ideas?

re: i5000 auto off timer
I didn't find a specification on this, so I just timed the auto off on my unit. I turned it on and waited for it to zero. Then I looked at my watch and waited until the scale turned itself off. 1 minute 10 seconds. So, I guess the auto-off is on a one minute timer starting when the scale has decided that it's stabilized.

re: strain gauges
It is possible to damage a strain gauge by applying too much force. At some point, the device will be unable to return to its normal shape. That's why you shouldn't put anything more than 11 pounds on an 11 pound scale.

re: hypothetical computerized beam scales
Wouldn't you need at least one strain gauge to tell if the two sides are balanced? Or one at the fulcrum to see if the needle was pulling to one side? The system would still have to wait for the oscillations to settle before a reading could be made because otherwise it would detect imbalance and keep swinging masses around on the beam. Interesting concept though. It appeals to the nerd in me... I wonder if you could do something with accelerometers. I'll think about it some more tomorrow (if I get some free time).

Michael
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PostPosted: Wed Jan 04, 2006 9:52 pm    Post subject: Reply with quote

re: moisture content...

I don't know about flour, but I'm thinking that there must exist some ingredients that can vary in moisture content up to some point without drastically changing in bulk volume. Maybe they'd be horribly stale and unfit for use at that point, but this is a hypothetical question.
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PostPosted: Wed Jan 04, 2006 9:53 pm    Post subject: Reply with quote

I want to start off by saying that I love your site and it's a great resource. However, I think you may be confusing the term "precision" with the more correct term: accuracy. When discussing measurement, precision is much more closely related to reliability. So long as we are discussing baking as a science, I feel this is an important distinction.

Thanx, keep up the great work.
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PostPosted: Wed Jan 04, 2006 9:53 pm    Post subject: Reply with quote

^
I just realized that I misread and you had it right all along, nevermind.
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PostPosted: Wed Jan 04, 2006 9:53 pm    Post subject: Reply with quote

Does anyone know of any scales that have a high enough capacity for use in the kitchen and measure in increments of .1 g?
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Russell Coleman
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PostPosted: Wed Jan 04, 2006 9:58 pm    Post subject: Reply with quote

I bought the TH-9802L digital scale at Target. It has a capacity of 4.5 pounds. It measures in increments of .005lbs in pounds mode or .01oz in ounces mode. I use it all the time and am very happy with it.
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PostPosted: Wed Jan 04, 2006 9:59 pm    Post subject: Reply with quote

^ Still too much error... Oh well, looks like I'll have to buy 2 scales.
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