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UC Food Safety

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Why does my pesto turn brown?

I don’t know if plant scientists make better chefs, but knowledge of plant science can certainly improve our cooking. Take, for example, understanding how to handle oxidation, the interaction between oxygen molecules and all the many substances they may contact. Oxidation is what makes your fender rust and your copper penny turn green. As it relates to plants, oxidation is what causes fresh-cut produce to turn brown and wine to lose its flavor when left too long in an open bottle.

Perhaps you know how to thwart oxidation when preparing potatoes and serving sliced apples (and if not, we’ll get to that in a minute) but here is a less-common food that often falls victim to oxidation: pesto. Has this happened to you? You gather an armload of picture-perfect basil, blend it together with olive oil, pine nuts, garlic and cheese and produce a fantastic pesto sauce for your spaghetti. Fresh from the blender, it’s as green as your holiday tree. But by the time you serve it an hour later, it’s a dull shade of olive brown and has lost much of its taste. Oxidation strikes again.

Here’s a handy plant-science trick: Blanche your basil. Heat destroys the enzymes that cause oxidation and the resulting discoloration. Drop your fresh basil in a pot of boiling water for a few seconds and then shock it in a bowl of ice water. Dry it completely, proceed with your favorite recipe and your pesto will stay green and tasty for days. Here’s the recipe I like to use:

  • 2 cups packed fresh basil leaves
  • 2 cloves garlic 
  • 1/4 cup pine nuts (I use walnuts when I don’t have pine nuts) 
  • 2/3 cup extra-virgin olive oil, divided (for special treat, try using a UC Davis olive oil    
  • Salt and pepper, to taste
  • 1/2 cup parmesan or other hard cheese

Combine the basil, garlic and nuts in a food processor or blender and pulse until coarsely chopped. Add 1/2 cup of the oil and process until fully incorporated and smooth. Season with salt and pepper.

If you’re eating it right away, add all the remaining oil and pulse until smooth. Transfer the pesto to a large serving bowl and mix in the cheese. Yum! If you’re freezing it (up to three months), transfer to an air-tight container and drizzle remaining oil over the top. Thaw and stir in cheese. 

You can also stop oxidation by treating fruits and vegetables with ascorbic acid immediately after cutting. Ascorbic acid is a natural property in many citrus fruits, such as oranges and lemons. Vinegar works, too, but that’s not something you usually want to put on fruit like fresh-cut apples. Instead, squeeze a few drops of lemon or orange juice on the cut side and they’re good to go. One last tip before we both get cooking. Mashed potatoes are a great side dish this time of year, but all that last-minute preparation can be hard to manage. Wouldn’t it be nice if you could peel and cut the potatoes even a day in advance without them turning brown? You can. Place freshly cut potatoes in a bowl, cover with water, squeeze in the juice from two lemons and they will sit happily in your refrigerator for 24 hours. Drain, cook, mash and serve.

You can learn more about handling fresh-cut produce at the UC Davis Postharvest Technology Center and explore the joys of plant science at the UC Davis Department of Plant Sciences website.

Happy holidays!

Posted on Thursday, December 23, 2010 at 8:17 AM

Roasting chestnuts without an open fire

One of the great things about living in California is the year-round farmer's market. Winter brings an array of winter squash, kale and chard, pomegranates, and citrus - including my favorite, the Satsuma mandarins that can be eaten like candy.

And of course, chestnuts. When we make it to the Sunday Sacramento farmer's market, one of my favorite stops is for roasted chestnuts.

Fun as it is to buy freshly roasted chestnuts, you can do it yourself and you don't need an open fire. They're incredibly easy to roast in your oven.

Preheat your oven to 450º and place the oven rack as close to the bottom of the oven as possible.

The next very important step is to cut an "x" into each chestnut to allow steam to escape.  You can do this with a regular serrated knife - you don't need a special chestnut knife. Miss this step and you'll have a big exploded chestnut mess in your oven.

Lay the chestnuts in a single layer on a roasting pan, sprinkle with water, and place in the oven.  Roast for 15 minutes, then turn them over, and sprinkle with water again.

Roast for another 15 minutes, or until the skin has started to peel back and the inner meat is soft. Take them out of the oven and allow them to cool.  Peel and eat them as soon as they are cool enough to handle! The chestnuts are easiest to peel when they're warm.

Chestnuts are highly perishable and need to handled and stored differently from other types of nuts. So if you buy them at the market, plan on roasting them within two days. There is more on storing chestnuts in ANR's free publication Nuts: Safe Methods for Consumers to Handle, Store, and Enjoy.

And if you want to try your hand at growing your own chestnuts - ANR has also published a handy guide to Chestnut Culture in California.

Posted on Tuesday, December 21, 2010 at 6:27 AM

Growing food and community

A wonderful example of community coming together in partnership to grow good food has taken root in Oxnard, Calif.

Last year, in an effort to reduce costs while improving the taste and nutrition of meals, the Senior Nutrition Program began growing their own tomatoes. They set up their garden with the help of UC Master Gardeners on a quarter-acre behind the Juvenile Justice Center.

The program began when the County of Ventura Area Agency on Aging, which serves over 200,000 meals annually through senior nutrition programs, collaborated with the Probation Agency Juvenile Justice Facility staff to create this positive program. As word of the project has spread many business and organizations have come forward to donate time, expertise and resources.

A year later, the garden has grown to two acres. Fifty fruit tress and a wider assortment of vegetables have been added. Ventura County Cooperative Extension Master Gardeners teach incarcerated youth gardening skills. Senior volunteers work alongside youths, mentoring while tending the garden. All produce grown at the garden is used to feed seniors through senior meal programs and local food banks.

This project, as well as others like it, take time, effort and dedication to get started; however, the positive benefits come back many times over. Looking to start a similar project in your community? Contact your local Cooperative Extension office for resources in your area. Or check out UC ANR publications that can help you and your group. Some are available free and others may be purchased online.

Posted on Thursday, December 16, 2010 at 6:24 AM
  • Author: Chris M. Webb

Food, hand-washing and the ick factor

Very few people wash their hands adequately prior to preparing or eating food. Most of us don’t even know how to wash hands properly.

There are many good reasons to wash hands:

  • Pathogen spread – from yourself, from others, from one contaminated food to another (meats, produce, etc.)
  • Chemical spread – whatever chemicals are on your hands can go directly into the food being prepared. This can include pesticides, hand sanitizers (ick), cleaning products, hand lotions, etc.
  • The ick factor – “Ick, what’s that slime on your hands and do I really want that in my food?”

The most memorable item I learned about hand-washing is that we need to wash for at least 20 seconds — the time it takes to sing the entire “happy birthday song” twice (and slowly). Watch anyone in any kitchen or public bathroom, and very few come close to washing for that long.

It’s human nature to think that our own hands are cleaner than everyone else’s, and that maybe we ourselves have less need to wash our own hands before preparing food for others. Well, everyone benefits if we all wash our hands well before cooking or eating.

Many years ago I got giardia, which laid me out for weeks, and my doctor and I determined that I probably got it from a food-service worker who did not wash hands properly. A big “ick.” It was a real wake-up call about the need for hand-washing.

So, if you hear me singing the happy birthday song while washing my hands in the kitchen, you can be thankful for my commitment to good hygiene.

Guidelines for hand-washing

  • Wet your hands with clean running water
  • Apply liquid, bar, or powder soap
  • Lather well
  • Rub your hands vigorously for at least 20 seconds. Remember to scrub all surfaces, including the backs of your hands, wrists, between your fingers and under your fingernails
  • Rinse well
  • Dry your hands with a CLEAN or disposable towel or air dryer
  • If possible, use your towel to turn off the faucet

(Information on hand-washing and using hand sanitizers can be found at the information sources below.)

Information sources for handwashing

Lastly, while we’re addressing kitchen sanitation, please use a clean tasting spoon each time you sample what you are cooking. It’s a really big ICK to taste from the stirring spoon, then put it back into the food. It’s also a way to spread germs, especially in uncooked foods. Yes, cooking may sanitize the spoon, but people still don’t want to eat other people's saliva, sterile or not.

Happy holidays, and stay clean and healthy!

UPDATE (Dec. 15, 2010): A new press release from the Centers for Disease Control and Prevention reports that 1 in 6 people get sick from foodborne illnesses each year. The CDC also reports that keeping hands clean is one of the best ways to prevent the spread of infection and illness.

Posted on Wednesday, December 15, 2010 at 9:18 AM

Feeding the world: Top 100 questions for agriculture

When looking for good answers to big problems, you better make sure you’re asking the right questions – especially when you want to put food on the global table for 9 billion people.

That’s exactly what a team of 55 agricultural and food experts from the world’s major agricultural organizations, scientific societies and academic institutions did recently when they identified the top 100 questions that must be answered if the world is to increase food production by 70 to 100 percent by 2050, when the world’s population is expected to reach 9 billion. Their list appears in the International Journal of Agricultural Sustainability. A PDF of the article is linked at the end of this post.

The top 100 questions cover 13 priority themes and are intended to help frame the research, policy and funding agendas for global agriculture. They were selected from an initial list of 618 questions that had been identified by a core group of experts representing universities, United Nations agencies, research institutes, non-governmental organizations, foundations and regional research secretariats in 23 countries.

Co-author Thomas Tomich, director of the Agricultural Sustainability Institute at UC Davis, predicts that global agricultural and food systems will have to change substantially to meet the growing worldwide demand for food. Looming issues such as climate change, water stresses, energy insecurity and dietary shifts won’t make the challenge any easier, he says.

“California is a hub for technological and scientific innovation, and we can set the pace for a transition to a more sustainable food system, providing inspiration and insights for the world,” Tomich said. “Indeed, if we cannot pull this off in California, who can?”

He noted that it is imperative for the scientific research agenda to keep abreast with the challenges of global food production.

“For California agriculture to stay at the cutting edge in a competitive food system that is facing increasingly complex challenges worldwide, our researchers need to be engaged globally,” he said.

UC Davis' Agricultural Sustainability Institute was founded in 2006. The finstitute is committed to helping ensure access to healthy food and promoting the vitality of agriculture today and for future generations through integrative research, education and communication efforts. The institute includes the UC statewide Sustainable Agriculture Research and Education Program, the UC Davis Russell Ranch Sustainable Agriculture Facility and the UC Davis Student Farm. 

Posted on Friday, December 10, 2010 at 1:24 PM

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