* Q1 sales volumes up 19.5 pct, below expectations
* Co cites capacity constraints in W. Europe
* Sales revenue of 1.515 bln CHF vs 1.496 bln forecast
* CEO sees overall chocolate market picking up
* Confirms mid-term guidance (Adds CFO, CEO comments, analysts, shares)
ZURICH, Jan 15 (Reuters) - Demand for chocolate is picking up, boosted by strong sales of gourmet products, the world's biggest supplier to the industry said on Wednesday, as it blamed capacity constraints and a lull in outsourcing deals for slower growth in its sales volumes.
Barry Callebaut, which makes chocolate for the likes of Nestle and Mondelez, said on Wednesday consumers in the Americas in particular were flocking to premium chocolates.
That echoed comments from Swiss chocolate-maker Lindt & Spruengli, which beat full-year sales forecasts on Tuesday.
Consumer trends consultant Nielsen has said the global chocolate market grew 3.4 percent in volume from September to November, accelerating from 1.1 percent in the same period the year before, as economies recover in Europe and North America.
Barry Callebaut, the world's largest maker of chocolate and cocoa products, said its sales jumped 21.4 percent by value in the quarter - the first of its financial year - to 1.52 billion Swiss francs ($1.7 billion), beating forecasts and helped by higher prices for cocoa beans, cocoa butter and milk powder.
However, its sales volumes rose 19.5 percent, below the 21.1 percent forecast by analysts, and excluding the Petra Foods business it bought in December 2012, volumes were up just 4.6 percent, down from 8.3 percent the same time the year before.
The Swiss-based company blamed the slowdown on a tough year-on-year comparison, as well as fewer new deals to make chocolate for third parties. Bottlenecks in western Europe also weighed on growth in the region, though it said these were being addressed.
J. Safra Sarasin analyst Patrick Hasenboehler said the company's volume growth was "slightly disappointing" and kept a "reduce" rating on the stock, citing a stretched valuation.
But Vontobel's Jean-Philippe Bertschy said the slower volume growth reflected a drive by management to focus on higher-margin businesses.
Shares in Barry Callebaut, up almost 30 percent since the end of August, trade at 20.5 times forecast earnings, above Nestle's 18.6 times, according to Thomson Reuters data.
The stock was down 1.0 percent to 1,106 francs by 1015 GMT, underperforming Europe's food and beverages index.
Outsourcing, such as a 2012 deal with Unilever to supply chocolate for ice creams such as Magnum, has helped Barry Callebaut to outpace generally sluggish growth in the global chocolate market in recent years.
Some analysts have suggested that growth from outsourcing agreements may start to slow.
However, Chief Executive Juergen Steinemann said the company had a "full pipeline" of outsourcing deals.
The company confirmed its mid-term forecast for 6-8 percent volume growth on average.
Barry Callebaut saw quarterly volumes rise 1.5 percent in Europe, 10.3 percent in the Americas and 7.4 percent in the Asia-Pacific. Its cocoa unit performed particularly strongly with sales volumes up 91 percent driven by the Petra Foods deal.
($1 = 0.9008 Swiss francs) (Editing by Mark Potter)