When Chipotle Mexican Grill (NYSE:CMG) last reported earnings, it was another strong quarter. Sales were up 20%, comparable sales at locations open at least a year were up 10%, and earnings per share jumped a whopping 47%. Here's what the stock has done since:

CMG Chart

CMG data by YCharts.

With most expecting the burrito maker's comps growth to have slowed significantly as 2014's price increases have already had their full impact, should shareholders get ready for a letdown when Chipotle reports Tuesday? Let's take a look at what you should keep an eye on when Chipotle reports.

Food issues: good and bad
Unlike the controversies that have affected fast-food juggernauts like McDonald's and Yum! Brands around food safety, health, and poor quality in recent years, Chipotle has regularly been in the news because of its steps to improve its already industry-disrupting focus on quality, even when it affects supply and availability in the short term. 

A decision early this year to cut ties with a major pork supplier that wasn't meeting Chipotle's ethical standards on animal conditions still affects restaurants in about half the country, months after the move was made. It was only recently that the chain found a solution, going all the way to the U.K. to find a supplier that could meet its needs. It is still expected to take a few months for the supply chain to be back up to speed. 

More recently, Chipotle announced that it was removing the last of the GMO ingredients from its menu. While the pragmatist in me points out that billions of servings of GMO foods have been consumed by hundreds of millions of people for decades and there aren't correlatable rates of disease associated with this, Chipotle has consistently stated its position to use organic and non-modified ingredients as much as possible, as well as hold its suppliers to higher animal treatment standards. Whether you agree or not with the company's stance, its no-compromise position on sourcing continues to challenge the norm in fast food. 

On the other hand, beef prices continue to be a challenge for the company. In last quarter's earnings call, CFO John Hartung said that last year's price increase hadn't turned out to be enough to cover the skyrocketing cost of beef, and that the company expected to increase menu prices for beef items before the end of the third quarter. This has been especially driven by the fact that its sales mix didn't shift away from beef items after last year's price increase, as the company expected. 

In the interim, this could affect margins, but it's not clear how much. Co-CEO Steve Ells has regularly stated that they don't want to increase prices on a regular basis, but the beef situation could be forcing their hand. 

Sales growth likely to slow 
Over the past year, Chipotle's comps have been in the teens, an insanely high level for any store and largely driven by those price increases from 2014. The growth began slowing last quarter, with its 10% comps growth the lowest in a year as 2014's price increases happened in that year-ago period. 

Management said that about 6 percentage points of last quarter's 10% comps growth was attributed to the price increase, so the easy math is for comps to be closer to 4% this quarter, which would be in line with management's projection of low- to mid-single-digit growth. 

This is also likely to bring down total sales growth of 20%. Analysts expect $1.22 billion on average, which works out to a 16% increase from last year's second quarter. Earnings are predicted to increase 27% to $4.46 per share, as the company's growing scale and emphasis on operational efficiency pay off. 

Remembering the bigger picture 
This is a repeat of something I wrote last quarter: While sales and comps growth are important over time, don't let Mr. Market's short-term reaction to the results dictate your actions. Since the Q1 2014 earnings release in April of that year, Chipotle's stock has fallen in the days following more often than not. But it's soundly beating the market:

CMG Total Return Price Chart

CMG Total Return Price data by YCharts.

However, it's also underperforming the market since last August, and most of its gains are due to only a few very strong days.

The point? Over time, Chipotle has been a market-crushing stock because of the quality of its business, its culture, and the execution of its leaders. Trying to time your way in or out of the stock is risky and unlikely to pay off. When you dig into the earnings release, focus on operational execution: What is the company doing to drive down costs and make its restaurants operate more efficiently while still living up to its own food-quality standards? Over time, these are the things that will determine if it remains a great investment. 

Jason Hall owns shares of Chipotle Mexican Grill. The Motley Fool recommends Chipotle Mexican Grill. The Motley Fool owns shares of Chipotle Mexican Grill. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.