Of Chickens and Viruses

If you live in the US, you most likely have two egg-color options at your grocery store or farmers' market: white or brown. The color of these eggs doesn't affect flavor or nutritional content of the eggs - it just depends on the breed of chicken that layed them. However, if you have a Araucana, Dongxiang, or Lushi chicken (and if you do, you probably don't live in North America) they will probably lay blue eggs. A recent study in PLoS Genetics has shown that the reason for this is a retrovirus, EAV-HP, that has affected the chicken and turned it's eggs blue. But how can a virus affect eggs color?

The answer lies in how retroviruses work. Retroviruses use RNA as their genetic material (instead of DNA like we do). However, when the virus infects a host cell, it uses an enzyme called Reverse Transcriptase to translate it's RNA genome into DNA. This DNA is then inserted into the host cells' DNA genome, essentially tricking the host cell into using the information in the new DNA to make more retroviruses. The most famous retrovirus that affects humans is probably the Human Immunodeficiency Virus, shown in the image above (green) infecting a human lymphocyte (pink). Sometimes, when a retrovirus inserts a gene into the host DNA, it can change or affect the expression of genes around the insertion point. This is what happened with the blue egg-laying chickens.

In the case of EAV-HP, the virus inserted near a gene for a membrane transporter called SLCO1B3 and turned it on in the chicken uterus. This change allows the developing eggs to take up a bile pigment called biliverden from the chicken's body, turning the egg blue. Because this gene became part of the chicken's DNA, it is able to pass on the trait to it's offspring. Due to preferential breeding of Araucana, Dongxiang, or Lushi chickens that have this trait, most chickens of these breeds now lay blue eggs. The exact DNA sequences near theSLCO1B3 genes in these breeds is different, suggesting that the retrovirus caused the DNA changes that result in blue eggs in independent events in all three breeds. Both the blue pigment and the retrovirus involved are completely harmless to humans, so if you see a blue egg, don't hesitate to fry it up and enjoy!

(via BoingBoing)
(Image: Human Immunodeficiency Virus (HIV-I), a Creative Commons 2.0-licenses image from Microbe World's photostream)

DIY Chicken Stock

(this is NOT chicken stock)

Once you figure out that making home made chicken stock isn't difficult, you'll look back with shame and sadness at all of the wasted roast chicken carcasses of your pre-enlightenment days.

Home made chicken stock is full of finger-licking goodness due to the presence of gelatin. Gelatin is formed when collagen, a protein found in animal connective tissue, is hydrolyzed (broken down). This process takes some heat and time to occur. That's why bones, tendons, ligaments and cartilage, though not tasty on their own, become tasty through the miracle of a long, slow simmer. It's also this finger-licking-goodness that you miss when you use powdered stock - it generally contains salt and chicken flavor but lacks delicious hydrolyzed proteins. Stock that comes in a can or carton is better, but still can contain some artificial ingredients and is generally inferior to homemade stock.

Lucky for us, homemade stock is easy and cheap to make! The Kitchn has a great DIY guide to making home made chicken stock, but here is my take (somewhat similar, with some hacks to make it easier and a little cheaper).

Chicken Stock Protocol

Materials: roast chicken carcass, vegetable scraps, garlic (optional), whole black peppercorns (optional), 2 pots large enough to hold everything, strainer, cheesecloth, several containers to hold finished stock ( about 1-2 quarts per chicken)

1) Take the remains of one or more roast chickens (bones, cartilage, and bits of meat, avoid the skin) and put it into a pot that fits snugly.
2) Add in several handfuls of vegetable detritus. I use celery ends, carrot ends and peels, onion ends and skins, herb stems, etc., but use whatever you have got on hand. This makes great use of what is otherwise garbage and saves more useful veggies for another meal. Add in a couple crushed cloves of garlic and some whole peppercorns if you have them.
3) Cover the solids in the pot with about an inch of water. Bring to a low simmer for 3-4 hours - you will see some bubbles, but try to avoid a real boil.
4) Line a strainer with cheese cloth and place that inside another pot to catch the finished stock. Pour the chicken stock and solids through the strainer.
5) Aliquot stock into containers to be refrigerated (about a week) or frozen (indefinitely). For this purpose I like the re-usable twist-top storage containers or re-used takeout soup containers.

Notes:
- If you notice that there is a lot of fat floating on top of the stock, refrigerate overnight then remove the solidified fat with a spoon and then freeze or use the stock.
- If you don't have enough time or materials to make stock after roasting a chicken, put the parts in a bag or plastic container in the freezer until you do have time. In the mean time, toss any veggie scraps that you generate into the container for making stock.
- This method can be used for any amount of chicken leftovers - just scale up.
- You can also make other kinds of stock this way - try turkey stock after Thanksgiving, or buy a bunch of soup bones and make beef stock.